Now we'll finally be turning our attention to the scientific study of mental disorders or psychopathologypsychopathologyThe scientific study of mental disorders — their symptoms, causes, and treatments. (from the Greek psyche - “mind” pathos - “suffering” and logos - “study”). This chapter will cover approaches to defining abnormality, the challenges of diagnosis, and the main classifications and criteria for psychological disorders; illnesses of the mind which cause distressful thoughts, feelings, or emotions.

If we want to study abnormality, how do we decide which behaviors, thoughts, or emotions are normal? Of those that are abnormal, how do we decide which should be considered disorders?

One way of determining abnormality is familiar to us already: using a normal distribution or bell curve to determine statistical abnormality. If you measure a trait in a large enough sample of people, chances are you'll find some people who are several standard deviations from the mean and thus could be considered abnormal. If you measured height, you might find extremes at either end represent abnormalities related to illness or disease, such as dwarfism or gigantism. But just because something is statistically abnormal doesn't mean that it is a problem. Having green eyes is statistically abnormal (only about 2% of people) but this doesn't mean it is an illness that needs to be treated. Similarly, if depression becomes common among many people, it will still be considered a disorder that needs to be treated.

For these reasons, statistical abnormality alone cannot determine whether something is a mental illness. People vary in many ways, but only some variations are considered to be disorders. How do we determine which differences represent disorders, and which represent acceptable variations? We shouldn't forget that some behaviors previously classified as disorders, such as homosexuality (listed as a disorder until 1973), are no longer viewed as such, demonstrating how thinking can change on acceptable variations in people and their behaviors.

If societal views can influence whether something is defined as a mental illness or not, we might wonder if all disorders are societal inventions. Thomas Szasz argued just that, claiming that mental illness is a myth created by some members of society to control others. Szasz has argued that “problems in living” don't necessarily indicate “disease”. Mental illnesses involve judgment and thus are inherently tied to a social context, not just a biological one. Though Szasz first wrote these arguments more than 50 years ago, many of his criticisms still stand and there are not yet objective biological tests for the diagnosis of mental disorders.

Mental illness is diagnosed according to a medical model. This means that disorders or syndromes are considered to be clusters of symptoms; features believed to indicate disease. Symptoms can be categorized as positive symptomspositive symptomsIn schizophrenia, symptoms representing added experiences not normally present — hallucinations and delusions., which are not seen in healthy people, or negative symptomsnegative symptomsIn schizophrenia, symptoms representing deficits in normal functioning — flat affect, avolition, alogia., which refer to the absence of behaviors that are common in most people. Terms for negative symptoms can often be identified by the prefix a- or an-, Greek for “not” or “without”, as in anhedoniaanhedoniaLoss of interest or pleasure in activities previously found enjoyable — a core symptom of depression. - “without pleasure”, a loss of pleasure that can be a symptom of depression.

Just as your physician looks at a combination of symptoms (cough, sore throat, and fever) to identify an illness such as influenza, a psychiatrist considers a particular combination of symptoms to diagnose a mental disorder. As with other illnesses, symptoms may overlap, which can make diagnosis difficult. Is your fever a sign of influenza or some other infection? Is your sleep disturbance the result of a sleep disorder, or is it related to some other disorder such as depression? This becomes even more complicated when we consider that mental illnesses are often comorbid, meaning that more than one illness may be present at one time.

One approach to understanding mental illness focuses on physiology, suggesting that psychological disorders arise from problems in the body. This is known as the somatogenic hypothesis. Or we may consider how thoughts and psychological factors could play a role in causing mental disorders, known as the psychogenic hypothesis. Finally we could consider the role of culture, society, and experience, and adopt a learning perspective.

As you might guess, none of these approaches should be seen as THE approach to understanding mental illness. All of these factors may play a role in the development, progression, and possible treatment of mental illness, leading us to a biopsychosocial approach (or multicausal model).

This approach includes considering the role that gender plays in mental illness. While gender differences can be observed in many illnesses, the underlying causes for these differences are not clear. They may result from differences in hormones, thinking patterns, or societal expectations and cultural pressures, all of which can vary by gender. Males and females may experience different levels of stigma, or feelings of disgrace, attached to seeking help or showing certain emotions. There may be unspoken cultural rules for how men and women express symptoms and how those symptoms are interpreted. All of these may play a role in the emergence, diagnosis, and treatment of mental illness.

When it comes to deciding if certain symptoms are part of a disorder, you can remember the three D's of disorder: deviancedevianceBehavior that differs markedly from what is considered normal or acceptable within a cultural context., dysfunctiondysfunctionImpairment in daily functioning — work, relationships, or self-care — caused by a psychological disorder., and distress.

Deviance refers to thoughts or behaviors which are considerably different from normal and are uncommon or unacceptable. Would most people do this if they were in a similar situation? Defining deviance necessarily involves social and cultural norms: screaming at the top of your lungs and dancing violently might be normal at a rock concert, but this behavior would probably be considered deviant in a lecture hall.

Dysfunction refers to maladaptive behaviors which interfere with the ability to live a normal life. Thoughts, behaviors, or emotions that impair the formation of social relationships, cause occupational difficulties, or disrupt daily life would be considered dysfunctional.

Distress refers to causing pain or making a person upset. Some deviant or even dysfunctional behaviors are not distressing and thus may not represent disorders. In some cases, however, distress may be felt by others rather than the person with the disorder (as in antisocial personality disorderpersonality disorderAn enduring, inflexible pattern of inner experience and behavior that deviates from cultural expectations and causes distress. in which the person's disregard for others doesn't distress the person with the disorder but may harm others).

There are a few other D-words that can relate to diagnosis. Danger, to oneself or others could range from the extremes of suicide or homicide to the mundane like failure to take care of one's health or maintain a clean and safe living environment. Potential symptoms are considered based on their duration. So depressed mood lasting for a day or two is not considered a symptom (even though it causes distress and dysfunction), but it can become a symptom if it lasts for several weeks.

Keep in mind that many symptoms of mental illness are common and their diagnostic usefulness comes not from their mere existence but from their frequency and severity. One challenge of diagnosis is determining just how severe or persistent potential symptoms are during brief consultations. Limited information can lead to misdiagnosis, but multiple lengthy consultations could unnecessarily delay treatment for those who need it.

While psychiatrists frequently use carefully designed inventories with specific questions and limited options for responses, they also use semi-structured interviews with open-ended questions to assess symptoms and signs of mental illness. We might see psychiatrists as torn between the need for objectivity (with the dry checklist mentality that entails) and the need to connect with patients on a human level in order to encourage trust and openness (despite the subjectivity this can create). The same can be said for all physicians; bedside manner matters and plays a role in the description and interpretation of symptoms, compliance with treatment regimens, efficacy of treatment, and overall patient well-being.

In 1973, David Rosenhan published a study which disrupted the mental health community and questioned the ability of psychiatrists to recognize and diagnose mental illness, the way patients were treated, and the long-term consequences of mental health diagnoses.

8 healthy pseudo-patients (3 women and 5 men) went to 12 different hospitals and claimed to be hearing voices saying things like “empty”, “hollow”, and “thud” (these words were chosen specifically because there were not any recorded cases matching them). Based on the one symptom of hearing voices, a diagnosis of schizophreniaschizophreniaA severe disorder involving positive symptoms (hallucinations, delusions), negative symptoms (flat affect, avolition), and cognitive impairment. was given 11 times (and a diagnosis of manic-depressive psychosis was given once) and the pseudo-patients were all admitted. The pseudo-patients gave false names and occupations to disguise that some of them worked in the mental health field but truthfully answered other questions during their assessments. Rather than raising skepticism, these otherwise-normal personal histories were frequently interpreted as pathological.

One explanation for this is that most people who seek consultation with a psychiatrist are assumed to need help. Healthy people don't usually decide to spend an afternoon waiting in the emergency room just for something to do, and the same is assumed to be true for those at a mental health facility. With this in mind, it may seem fair that psychiatrists assume an illness and focus their energies on figuring out which one to diagnose, rather than questioning whether there is any illness at all.

Once admitted, the patients faced the challenge of convincing staff they were sane in order to be released. This was no easy task and length of hospitalization ranged from 7 to 52 days, with an average of 19 days. Immediately upon admission, the patients claimed that their symptoms were gone and they behaved “normally” (though Rosenhan notes they may have shown some anxiety and fear, since they weren't expecting to actually be admitted so readily). Normal, sane behaviors such as keeping a journal were often interpreted as symptoms by staff. Ironically, Rosenhan noted that other patients were often more attuned to the sanity of the pseudo-patients than the psychiatrists and nurses, and said things like “You’re not crazy. You’re a journalist, or a professor (referring to the continual note-taking). You’re checking up on the hospital.”

None of the 12 hospitals recognized any of the pseudo-patients as fakers. Rather than casting doubt on the original diagnosis, discharge often led to “schizophrenic – in remission” on records, revealing the stickiness of labels in mental health. Labels can take a lasting place in medical records and allow stigma to follow patients for years after symptoms have been successfully treated. When our physical bodies heal we have no problem dropping the names of illnesses that have previously plagued us, so we don't call you “broken-legged” or “chicken pox-ic” for years after you've healed. Yet with mental health, there's a tendency to consider disorders as lasting traits, meaning that one-time diagnoses can become part of patients' identities, prolonging symptoms and reducing feelings of control.

Rosenhan's study helped remind psychiatrists of the many assumptions they were making. In fact, Rosenhan suggested he would send more pseudo-patients to hospitals in the future. Several facilities claimed to have identified dozens of these fakers in the months that followed, only for Rosenhan to reveal that he hadn't actually sent any.

The main classification system for mental illness in the United States is the DSM-5DSM-5The Diagnostic and Statistical Manual of Mental Disorders, 5th Edition — the primary classification system for psychological disorders in the US., the Diagnostic and Statistical Manual of Mental Disorders – 5th edition, released in 2013. This manual describes the symptoms and prevalence of each mental disorder as well as other associated features and how similar disorders can be differentiated from one another. You may notice that the DSM-5 does not use roman numerals like earlier editions (DSM-III or DSM-IV). More frequent incremental updates will be labeled like software updates such as 5.1, rather than V.I, which would look confusingly similar to the roman numerals for 6. The DSM-5 is not the only system of classification, and the ICD-10 (International Statistical Classification of Diseases and Related Health Problems – 10th edition) is more commonly used for clinical purposes in Europe. An updated 11th edition of the ICD is scheduled to be released in 2018 (after being pushed back multiple times).

The DSM-5 attempts to focus on objective criteria; symptoms which are observable, reliable, and easily counted. But this can be difficult when it comes to how patients describe their thoughts and emotions, if they are able to describe them at all. Patients may not have insight into their own symptoms and may be unable to recognize or explain them, meaning that a psychiatrist must make inferences. Patients may also have a tendency to misrepresent their symptoms, emphasizing or downplaying certain behaviors, feelings, or thoughts.

The monist assumption that everything psychological results from underlying physiology applies to mental illness, but this doesn't mean we should assume biological defects are the cause of all abnormality. We should accept that well-functioning biology can still give rise to behaviors which are deemed abnormal. This may explain why there are not yet any medically valid physiological tests for the illnesses described in the DSM-5. In other words, no blood test or brain scan can be used to diagnose depression, schizophrenia, or obsessive-compulsive disorderobsessive-compulsive disorderA disorder involving intrusive, unwanted thoughts (obsessions) and repetitive behaviors (compulsions) performed to reduce distress.. While there are biological factors associated with mental illnesses (such as neurotransmitter levels, hormone levels, etc.) these associations are not used to diagnose illness in the way that a blood test can diagnose anemia or hepatitis. While mentally ill people are often said to suffer from a “chemical imbalance”, no measurement of chemicals takes place during diagnosis, nor have any researchers provided a clear description of what an appropriate balance would be.

Without these kinds of objective criteria for diagnosis, reliability can become a problem. Will two psychiatrists seeing the same symptoms reach the same diagnosis? Aaron Beck and colleagues (1962) found that when pairs of psychiatrists assessed 153 patients then made independent diagnoses, only 54% of these diagnoses were in agreement. Reliability can also be an issue across cultures. John Cooper and colleagues showed video-taped clinical interviews of patients to psychiatrists in New York and London in 1972. They found that based on the same video of the same patient, psychiatrists in the US were twice as likely to give a diagnosis of schizophrenia while those in the UK were twice as likely to diagnose the same symptoms as an affective disorder (such as depression or bipolar disorderbipolar disorderA mood disorder involving alternating episodes of depression and maniamaniaA period of abnormally elevated or irritable mood, decreased need for sleep, grandiosity, and impulsive behavior. (bipolar I) or hypomania (bipolar II).). DSM updates have made an attempt to make criteria clearer in order to address these problems and ensure that the same diagnosis is reached regardless of which psychiatrist a patient visits.

The push for greater objectivity for the DSM-5 led to removal of the previous axial system and this represents a controversial ideological shift. In previous editions, the axial system included other potentially relevant medical illnesses as well as factors such as poverty and social support. While many psychiatrists and counselors consider mental illness part of a complex biopsychosocial process, the diagnostic criteria in the DSM-5 place less emphasis on how psychological or social factors contribute to disorders.

In addition to listing symptoms, the DSM-5 provides information on the prevalence of most disorders, usually expressed as a percentage. The prevalence tells us how frequently a disorder occurs, either over the course of one's life (lifetime prevalence) or during a particular time period (point prevalence). For example, the point prevalence of bulimia nervosa is much higher for teenage girls and young women than for older women. If a woman has not suffered from bulimia before age 40, her risk of developing the disorder drops considerably. Most of the prevalence estimates provided in the DSM-5 are based on 12-month periods of time, indicating the percentage of people in the population with that diagnosis during the course of a single year, so lifetime prevalence estimates will often be higher than 12-month prevalence estimates.

To be clear, prevalence refers to the total number of cases of an illness at a given time. This differs from incidence, which refers to the number of new cases which have appeared in a given time period. Prevalence tells us how widespread an illness is, not the risk of contracting it. Imagine a virus outbreak with high incidence only in a particular year (say 2014). If this infection takes longer than a year to cure, then in 2015 incidence could be low (very few new cases) even though the prevalence would still be high (many people are still infected).

The DSM-5 also indicates comorbiditycomorbidityThe co-occurrence of two or more disorders in the same person., listing disorders that are frequently diagnosed in the same patient. We can't simply add prevalence rates to estimate how many total people are diagnosed with mental illnesses because disorders tend to be more highly concentrated among a smaller group of people who are each diagnosed with several disorders.

While there are genes which predispose people to certain mental illnesses like depression or schizophrenia, genes are not fate and are not solely responsible for these illnesses. The diathesis-stress modeldiathesis-stress modelThe view that disorders develop when a biological or psychological vulnerability interacts with environmental stress. for mental illness suggests that people may have a predisposition for a disorder (or a diathesis) but that environmental or psychological events (stress) cause the disorder to be expressed (or not). The level of predisposition and the amount of stress needed to reach a threshold will vary for different individuals, explaining why the same environmental stressor can trigger a disorder in some people but not others.

This graph is oversimplified, however, as environment may influence gene expression (epigenetics) and genes may influence response to environmental stress. This interaction can be seen in a study by Avshalom Caspi and colleagues (2003) which found that versions of a serotonin transporter gene may influence an individual's response to stress. This means that people with a particular version of the gene are at greater risk for depression, but only if they also experience certain levels of stress.

What role does culture play in the prevalence, expression, and understanding of mental illness? Culture can determine which behaviors are considered abnormal. Refusing to leave the house alone could be seen as a symptom of agoraphobiaagoraphobiaFear and avoidance of situations in which escape might be difficult during a panic attack. for a woman in the US, but in some cultures this behavior might be the result of expectations and pressures, rather than a sign of internal dysfunction. The DSM-IV listed culture-bound syndromes, which were disorders considered to be culturally or geographically localized. One such disorder was koro, an intense anxiety that the penis is retracting into the body and will cause death (women may have symptoms of koro related to retraction of the nipples, breasts, or labia), though there are not any actual physiological changes. Most cases of koro have occurred in Southeast Asia, though it has also been reported in West Africa.

The DSM-5 has done away with the term “culture-bound syndrome” and replaced it with three terms for discussing the role of culture on mental illness: cultural syndromes which tend to co-occur among individuals in specific groups, cultural idioms of distress for how groups express symptoms or syndromes, and cultural explanations of distress or perceived causes, which are culturally-recognized meanings or etiologies for symptoms, illness, or distress.

Other cultural syndromes include dhat (semen-loss anxiety) in India, ataque de nervios “nerve attack” in Latin America, and 神经衰弱 shénjīng shuāiruò or “nerve weakness” in China. Are these specific disorders based on culture, or are these just differing expressions of the same universal disorders? Do disorders like shénjīng shuāiruò, which emphasizes nerves and the physical body, provide a way for people to sidestep the stigma associated with mental illness in their culture?

Shénjīng shuāiruò and ataque de nervios carry complex cultural baggage, but a diagnosis of depression provides a clear path to treatment: prescription of antidepressant medication. Is replacing cultural ideas of illness with universal disorders a way for pharmaceutical companies to increase their global reach? This cynicism isn't unfounded. A marketing campaign by GlaxoSmithKline in Japan introduced the idea of mild depression as a common problem and sales in the country quintupled between 1998 and 2003. We shouldn't be too cynical, however, as this campaign may have helped to raise awareness and reduce stigma, both of which may have improved people's lives.

In the next sections, we'll see disorders from several categories of the DSM-5, as well as their symptoms, prevalence, and associated factors. In looking over symptoms, remember that not all symptoms are necessary for a diagnosis. Usually, there will be a specified minimum number of symptoms for each criteria relevant to a diagnosis. Where do these numbers come from? These numbers were chosen by the DSM committee, based on discussion and voting as to how many symptoms are needed to meet a criteria. So if we ask why 5 symptoms are needed for a particular disorder, rather than only 4 or instead of 6, there's not always an objective research-based answer. To be fair, the DSM recognizes this problem, generally by having an unspecified disorder listed for those people who meet many of the symptoms of a disorder but do not fulfill the full criteria for diagnosis.

The DSM-5 recognizes 10 classes of substances which are known to cause symptoms of other disorders. If symptoms appear within 1 month of intoxication or withdrawal from these medications, drugs, or toxins, symptoms may represent a substance/medication induced disorder. (It is also noted that some toxins or hallucinogenic drugs may cause neurocognitive or perceptual symptoms which persist for longer than one month). This means that there are diagnoses in the DSM-5 which many people would qualify for at some point but which do not really represent mental illness. These include alcohol intoxication (for which the DSM-5 gives an estimated 12-month prevalence of 70% among college students), caffeine intoxication, cannabis intoxication, and tobacco withdrawal.

Before we begin discussing the symptoms of particular disorders, it's important that we remind ourselves that many symptoms are common. We should avoid falling ill to medical student's disease: in which medical students begin to feel they have all the symptoms they are learning about. The information in this chapter is to help you understand mental illnesses, not diagnose them. Just as you may see symptoms in yourself, you may see potential symptoms in others but you should avoid making assumptions about their mental health.

As you learn these diagnostic terms, remember that they shouldn't be thrown into everyday conversation as adjectives. These disorders represent real struggles for many people. Saying things like “I have to wash my hands, I'm so OCD” or “I'm so anorexic” because you didn't eat much at a meal can trivialize the suffering of others, or worse, discourage them from seeking help.

I've tried to provide a broad overview of mental illness, so some disorders are included for reference purposes. Don't be overwhelmed or feel you need to memorize all of the disorder names, symptoms, and prevalence estimates. This list isn't meant to be comprehensive but it should give you a better understanding of the categories of mental illness and the symptoms associated with particular disorders. Remember that not all symptoms are necessary for a diagnosis and that severity, duration, and levels of distress are important when considering any possible symptoms.

A specific phobiaphobiaAn intense, irrational fear of a specific object or situation that leads to avoidance. refers to an irrational fear of a specific object or situation. While many people experience fear in the presence of snakes or spiders, people with a phobia experience an intense panic reaction; elevated heart rate, sweating, and difficulty breathing. One exception to this response occurs in specific phobias for blood, injury, or injections, in which patients show an elevated disgust response, rather than a fear response, so the sight of blood or a needle can result in fainting.

Specific phobias are characterized by irrational fear, meaning that the reaction occurs when the person is not in any danger, such as when looking at an image of the object. Of course, a fear of snakes, spiders, and other potentially dangerous stimuli is rational in some circumstances, and the fact that these specific phobias are common suggests an evolutionary link. Preparedness theory suggests that there has been an evolutionary advantage to learning some fear associations more easily than others. The DSM-5 gives a 12-month community prevalence in the US of 7-9% with women twice as likely as men to be diagnosed. Point prevalence is highest for 13-17 year-olds (16%) and lower for children (5%) and adults (3-5%).

You've probably seen exotic terms for specific phobias (i.e. arachnophobia – fear of spiders) but these terms are not part of the DSM-5. These are created using the Greek word for an object + phobia, creating familiar terms like claustrophobia – fear of enclosed spaces, as well as obscure terms like triskaidekaphobia – fear of the number 13 or coulrophobia – fear of clowns (which I'm pretty sure everyone has). For more, check out www.phobialist.com, unless of course you have epistemophobia- fear of knowledge.

Social anxiety disorderanxiety disorderA class of disorders characterized by excessive fear, anxiety, and related behavioral disturbances. (also known as social phobia) is a phobia for situations which carry a threat of scrutiny or evaluation, or the anticipation of these situations. Social situations almost always cause some anxiety and social situations with high risk of judgment may be avoided (such as meeting new people or public speaking).

Social anxiety disorderSocial anxiety disorderIntense fear of social situations where one might be judged or embarrassed. is associated with substance abuse (alcohol or other drugs) as a means of coping with social situations. The 12-month prevalence estimate is about 7% in the US, though estimates in other countries are considerably lower (median of 2.3% in European countries). Age of onset is usually between 8 and 15 years old, and prevalence is roughly equal for men and women.

Panic disorderPanic disorderRecurring unexpected panic attacks plus persistent concern about future attacks. is characterized by the occurrence of panic attacks; sudden episodes of heart palpitations, difficulty breathing, sweating, trembling, and a sense of terror that one is having a heart attack, going crazy, or dying. Unlike specific phobias, which are triggered by particular objects or situations, panic attacks occur unpredictably. This can cause anxiety over the possibility of having an attack in an embarrassing or dangerous situation. Attacks may occur consistently (once every week or two), or frequently (daily) for a short period of time, followed by weeks or months without incident. The estimated 12-month prevalence in the US and Europe is 2-3% with a female to male ratio of 2:1.

One specific phobia which has its own diagnostic criteria and label is agoraphobia. Sometimes translated as a “fear of open spaces” (from the Greek agora - “marketplace” or “public square”) this phobia refers to avoidance of situations in which it would be difficult to escape danger or receive assistance. This may include open spaces like fields or parking lots but it can also include enclosed spaces, public transportation, or crowds. People with agoraphobia tend to withdraw to places where they feel safe and may not leave their homes or bedrooms for days or weeks. Agoraphobia is often comorbid with panic disorder, as the fear of public panic attacks can cause people to become isolated. Agoraphobia has a 12-month prevalence of 1.7%, is twice as common in women, and occurs most during late adolescence to early adulthood.

Unlike specific phobias, panic disorder, or agoraphobia, all of which occur as episodes of intense anxiety, generalized anxiety disordergeneralized anxiety disorderPersistent, excessive, and uncontrollable worry about multiple areas of life. (GAD) refers to a condition in which anxiety is ever-present. This anxiety is not related to specific causes or may be caused by a wide range of situations, from continuous worry about loved ones to constant nervousness at work. This uncontrollable anxiety causes sufferers to feel on edge and can lead to irritability, difficulty concentrating, sleep disturbance, and fatigue. GAD has a 12-month prevalence of 0.9% for adolescents and 2.9% for adults. GAD is slightly more common in females, and males with GAD show greater comorbidity with substance use disorders.

Separation anxiety refers to persistent and excessive fear or anxiety when separated from home or from attachment figures. While temporary anxiety when separated from a caregiver indicates secure attachment in infants, separation anxiety is “developmentally inappropriate” and lasts for at least 4 weeks in children or 6 months in adults, resulting in significant impairment in social, academic, or occupational functioning. 12-month prevalence of separation anxiety is highest in infants (4%), lower in adolescents (1.6%), and lowest for adults (0.9-1.9%).

As mentioned in the chapter on stress, Post-Traumatic Stress DisorderPost-Traumatic Stress DisorderA disorder following trauma — characterized by intrusive memories, avoidance, negative changes in mood, and hyperarousal. (PTSD) involves recurrent, involuntary, and intrusive memories of traumatic events. In order to receive a diagnosis, one has to have experienced a traumatic event (not via television, movies, or video-games) or had repeated extreme exposure to aversive details (such as police officers or first-responders encountering victims, handling human remains, etc.).

Symptoms of PTSD typically emerge within 3 months of exposure to the traumatic event, though they may be delayed. Sufferers of PTSD often feel or act as if the event is occurring again and these dissociative reactions are referred to as “flashbacks”. Sufferers may avoid related stimuli, show a heightened startle response, and develop negative beliefs and distorted cognitions such as “my nervous system has been destroyed”.

The lifetime prevalence of PTSD is about 8%, with a 12-month prevalence of 3.5%. Prevalence is higher for certain groups such as military veterans, firefighters, medical personnel, police officers, and victims of rape, assault, combat, or captivity. While PTSD is commonly associated with men (especially military veterans), a greater number of sufferers are women who are victims of rape or violence. 80% of PTSD sufferers also meet the diagnostic criteria for another disorder, such as a depressive or anxiety disorder, or a substance use disorder.

While PTSD is a long-term effect of trauma, the short-term effects of traumatic events may lead to acute stress disorder; feelings of depersonalization and guilt which occur within 1 month of the event. Prevalence varies by event and acute stress disorder is estimated to affect 13-21% of those involved in vehicular accidents, 6-12% of those in industrial accidents, and 20-50% of victims of rape, assault, or mass shootings.

Other stressful events such as breakups, divorces, occupational problems, natural disasters, or even retirement can cause people to have emotional or behavioral symptoms and a level of distress which is considered out of proportion to the severity of the stressor. This may be diagnosed as adjustment disorder if distress causes impairment of social or occupational functioning. This disorder is considered to be a common psychological response to diagnosis of other serious medical disorders and illnesses and has an increased risk of suicide.

Obsessive-Compulsive Disorder (OCD) consists of two main symptoms: obsessions (recurrent, unwanted thoughts) and compulsions (repetitive behaviors). Common themes for obsessive thinking are thoughts of contamination, fears of harming others, or a need for symmetry and balance. OCD has a prevalence of about 2% and affects men and women equally. When untreated, OCD has a high comorbidity with depression.

To better understand the plight of OCD sufferers, imagine the brief anxiety you might experience from a thought such as “my hands are contaminated” after you've touched something unsanitary. You quickly find a place to wash your hands, the anxiety fades, and you move on to other thoughts. Now imagine that after you washed your hands, the anxiety didn't go away. This might compel you to wash again, and yet you still feel anxious and have thoughts of contamination. In order to reduce the obsessive thoughts and anxiety, you might begin performing compulsive behaviors which you know are irrational but seem to help, such as washing your hands multiple times, avoiding touching certain objects like doorknobs, or engaging in repetitive behaviors to distract yourself.

Previously considered a type of Obsessive-Compulsive Disorder, hoarding disorder now warrants its own diagnosis. The main symptom of hoarding is a difficulty parting with personal possessions (even those that are worthless) that is not due to obsessive thoughts, brain injury, autism, or decreased energy. This accumulation of clutter can cause congestion of the person's living area if others do not intervene and may cause social or occupational impairments or make it difficult to maintain a safe living environment.

80-90% of patients with hoarding disorder show excessive acquisition, acquiring items for which there is no available space. Some may also show animal hoarding, acquiring a number of pets for which they are unable to provide minimal standards of nutrition, sanitation, and care. Surveys indicate a prevalence of 2-6% for hoarding disorder affecting both genders equally. Hoarding is 3x more prevalent in older adults (age 55-94) and 75% of people with a hoarding disorder diagnosis have a comorbid mood or anxiety disorder such as major depressive disordermajor depressive disorderA mood disorder characterized by persistent depressed mood or anhedonia, plus associated symptoms, for at least two weeks. (50%) or OCD (20%).

The main symptom of Body Dysmorphic Disorder (formerly dysmorphophobia) is a preoccupation with perceived flaws or defects in physical appearance which are slight or not noticeable to others. These are commonly skin issues (scars, wrinkles, etc), but may be related to hair, teeth, facial features, or areas of the body. This preoccupation may lead to intrusive thoughts or repetitive behaviors (like mirror checking, excessive grooming, or reassurance-seeking) which are difficult to control and cause significant distress or social impairment. There may also be distorted thoughts such as “I look deformed” and self-ratings which range from feeling “unattractive” to feeling that one is a “monster”. While preoccupation with a flaw may lead to cosmetic surgery, only an estimated 7-8% of cosmetic surgery patients meet the diagnostic criteria for body dysmorphic disorder. The estimated prevalence is 2.4% in the US, affecting slightly more females than males. It is often comorbid with major depressive disorder.

This category of disorders replaces the somatoform disorders section of the DSM-IV. Two of the disorders in this category used to share the label hypochondriasis, which referred to a false belief in illness (which is not clear from the Greek roots for “under” and “cartilage”, which reference medieval beliefs about the location of melancholy under the sternum). This term has been divided into two disorders, which are differentiated based on whether or not somatic symptoms are present. Some patients previously diagnosed with hypochondriasis could now be diagnosed with somatic symptom disorder (if somatic symptoms are present) or illness anxiety disorder (if somatic symptoms are mild or non-existent).

Somatic Symptom Disorder refers to excessive thoughts, feelings, or behaviors related to somatic symptoms or associated health concerns. This leads to anxiety and sufferers devote excessive time and energy to symptoms and health concerns. Preoccupation with illness may become a focus of identity for the patient. While attention to symptoms may be excessive, the suffering of these patients is authentic and the most common somatic symptom is persistent pain, though normal bodily sensations may also be misattributed to illness. The estimated prevalence is 5-7% and is likely higher in females, who tend to report somatic symptoms more often than males.

Illness anxiety disorder involves excessive worry and anxiety that one has an illness, though one does not necessarily have any somatic symptoms of that illness (differentiating it from somatic symptom disorder above). There is still a high level of anxiety over health issues and preoccupation with illness, though potential symptoms are mild or non-existent. 12-month prevalence is similar for males and females and estimates range from 1.3 to 10%. Patients are frequently encountered in medical settings rather than mental health settings, since they believe they have a physical illness, not a psychological disorderpsychological disorderA pattern of thoughts, feelings, or behaviors that causes significant distress, dysfunction, or danger.. They may receive repeated negative diagnostic test results from multiple physicians and still persist in a belief in illness, though it's important not to be dismissive, as sometimes a patient may actually have a physical illness that is simply not being detected accurately.

Conversion disorder (also functional neurological symptom disorder) provides fascinating and puzzling case studies in neurology. This disorder is characterized by altered voluntary motor or sensory function and symptoms or deficits which cannot be explained by other disorders or are incompatible with other neurological diseases. These may include weakness, paralysis, abnormal movement or tremors, difficulty swallowing or speaking, and even seizures or loss of sensory function such as deafness or blindness. Physiological causes for these deficits cannot be found, and patients are not faking, so they are considered to be “functional” symptoms, or they may be labeled “psychogenic” (though as we've seen, the label “psychogenic” can be misleading, as underlying physiological mechanisms may exist but haven't been identified yet). Conversion disorder is quite rare, so prevalence is unclear but there are an estimated 2 to 5 cases per 100,000 people, affecting 2-3x more females than males.

Dissociation refers to a separation of some thoughts or experiences from conscious awareness. While dissociation may seem like a particularly bizarre symptom, you've probably experienced a few types of dissociation in everyday life. If you've ever felt unsure whether you did something or just thought about doing it, became so involved in a fantasy it felt real, driven a car and “lost time” or forgotten about part of the trip, talked to yourself when alone, or felt that a part of your body wasn't your own, then you've experienced dissociation, though likely not to the degree of the disorders below.

Dissociative experiences can also occur under the influence of drugs, such as blacking out from alcohol consumption or from the use of painkillers or anesthetics, whether having your wisdom teeth removed or falling into the “k-hole” reported by recreational users of ketamine, though you'll recall that the DSM-5 considers substance or medication induced symptoms differently than those which arise from internal dysfunction.

Dissociative amnesia refers to selective or global memory loss of autobiographical information, which may include a loss of identity. This is not ordinary forgetting such as misplacing your keys, it's forgetting where you live, who your family members are, or even who you are. Onset tends to be sudden and is typically preceded by a traumatic event. 12-month prevalence is estimated to be about 1.8% in the United States and dissociative amnesia is more than twice as common in women. In the US, nearly 50% of homicide cases involve defendants claiming to have memory loss for some or all of the events in question, though it's unclear whether this figure shows the extreme stress of those circumstances or a popular strategy by defense lawyers to reduce culpability. Amnesia occurring as a result of a physical injury (such as a blow to the head) would not be considered symptomatic of dissociative amnesia.

In some cases, dissociative amnesia and loss of identity is accompanied by what is known as a fugue state or a dissociative fugue, in which a person loses his identity, moves to a new location, and adopts a new identity. This new identity replaces the former one, and the person may have no recollection of prior life events, though these may be successfully recovered later. A character experiencing a fugue state is a somewhat common plot device for television shows, such as the Archer 4th season opener “Fugue and riffs” which began with Sterling Archer in a fugue state working at Bob's Burgers – a nod to the fact that actor H. Jon Benjamin voices the lead characters of both shows.

Dissociative Identity DisorderDissociative Identity DisorderA disorder involving two or more distinct personality states — formerly called multiple personality disorder. (DID), previously known as Multiple Personality Disorder (MPD), refers to a dissociation of identity which creates two or more distinct personality states. This disrupts the continuity of self and agency, and may also create gaps in memory. Some have suggested that this disorder manifests itself as possession in some cultures, though the DSM-5 diagnostic criteria clarify that symptoms should not be part of accepted cultural or religious practices. Some sufferers of DID may not be aware of their dissociative symptoms due to dissociative amnesia.

Prevalence is difficult to estimate, though the DSM-5 mentions a small community study with a 12-month prevalence estimate of 1.5% that was similar across genders. Other estimates, however, have been lower and suggest greater prevalence among women. Dissociation may be an attempt at coping with overwhelming experiences or traumatic events and an estimated 90% of DID sufferers previously experienced childhood abuse. This figure can be questioned, however, as some sufferers' memories of abuse were only uncovered through therapy, raising the possibility that these repressed memories or symptoms of DID were suggested by the therapist. DID is comorbid with PTSD, depression, anxiety, and substance use disorders and risk of suicide is high.

Depersonalized/Derealization Disorder refers to experiences of unreality or detachment, and the feeling that one is an outside observer of one's thoughts, feelings, sensations, body, or actions (often called an out-of-body experience). This may cause thoughts that one has no self or is no one. Some sufferers report knowing they have feelings, but not actually feeling them. This can cause diminished sense of agency for one's thoughts and actions and an altered sense of time. Derealization is a sense of unreality or detachment from surroundings, feeling that one is in a fog, dream, or bubble. Derealization may include sensory distortions such as altered distance or size of objects or voices sounding muted. Episodes of derealization may last for a few hours or as long as several days.

This disorder has a prevalence of about 2% and is equal for both genders. Despite the apparently bizarre symptoms, it's estimated that about half of all adults will briefly experience an episode of these symptoms at some point, though not severe enough to warrant a diagnosis.

This category of disorders refers to those with onset in the developmental period. These include things like intellectual disability, communication disorders (language, speech, stuttering, social communication), specific learning disorders (dyslexia, dyscalculia), and motor disorders (tic disorders and Tourette's syndrome).

Autism Spectrum DisorderAutism Spectrum DisorderA neurodevelopmental disorder characterized by deficits in social communication and restricted, repetitive behaviors. (also discussed in the development chapter) refers to a range of developmental problems related to language, motor skills, and socialization, including difficulty with recognizing facial expressions and other non-verbals. Those with autism may have problems understanding social relationships, have fixated interests, insist on rigid routines and rituals, or show repetitive motor behaviors such as hand-flapping or repeatedly saying idiosyncratic phrases.

Prevalence has increased rapidly in recent years, with the DSM-5 estimating prevalence at about 1% worldwide, though it is not clear whether this is due to the expansion of diagnostic criteria, increased awareness of the disorder, new methodology for assessment, or a true increase in the disorder. Autism spectrum disorder is 4 times more common in males than females and 70% of those diagnosed have a comorbid disorder (such as intellectual disability).

Attention Deficit/Hyperactive disorder (ADHDADHDAttention-deficit/hyperactivity disorder — a neurodevelopmental disorder involving inattention, hyperactivity, and impulsivity.) consists of two main symptoms: problems with attention, and hyperactivity. Attention problems include failures to pay attention to detail, carelessness, difficulty organizing tasks, following through, or sustaining attention, and frequent distraction and forgetfulness. Inattention is frequently accompanied by hyperactivity, which can be seen in frequent fidgeting, squirming, restlessness, and running and climbing in inappropriate situations. There may also be signs of impulsivity, such as frequent interrupting or intruding on others in conversations, games, and activities, or behaviors that lack foresight or impulse control. This combination of inattention and hyperactivity interferes with normal functioning or development.

Population surveys estimate prevalence of about 5% in children. Symptoms usually appear before age 12 and there's a 2:1 ratio of males to females. Adult ADHD is estimated to have a prevalence of only 2.5%, suggesting that people “grow out” of this disorder (or perhaps “grow into” improved executive function). A study of nearly one million Canadian schoolchildren indicated that the younger children are for their grade, the more likely they are to be diagnosed with ADHD. This suggests that faulty comparisons by grade (rather than age), are causing relative immaturity to be mistaken for illness (see Morrow et al, 2012).

In popular culture, schizophrenia is frequently confused with Dissociative Identity Disorder, likely due to the origins of the term, from the Greek schizo - “split” and phren - “mind”, coined by Swiss psychiatrist Eugen Bleuler. In schizophrenia, however, splitting refers to a disintegration of mental functions rather than a splitting of personalities or identities. Positive symptoms include delusions (false beliefs), hallucinations (perceptions of things not actually present), disorganized thought and speech, and abnormal motor behavior (catatonia). Negative symptoms include diminished emotional expression, anhedonia (lack of pleasure), alogia (diminished speech output), avolition (decrease in self-initiated purposeful activities), and asociality (decrease in social activities). Diagnostic criteria include at least 2 of the symptoms above which persist for at least one month (though some signs must persist for at least 6 months). Patients with schizophrenia may lack awareness of their symptoms, making it difficult to encourage them to seek treatment.

Cognitive symptoms include memory problems, difficulty with executive function and attention, and psychosis, which refers to losing contact with reality, resulting in bizarre beliefs and perceptions. Some patients with schizophrenia experience catatonia, locking the body into unusual positions which may be held for hours. Sometimes these postures are rigid and immovable, but at other times they may show waxy flexibility, in which the patient will maintain a body position but can be bent or moved by another person and will then hold the new position. While there is evidence of brain differences in neuroimaging, cellular architecture, white matter connectivity, and gray matter volume when comparing those with schizophrenia to healthy individuals, there are not currently any radiological or laboratory tests for schizophrenia, and it is only diagnosed through observation and assessment of symptoms.

The lifetime prevalence of schizophrenia is estimated to be around 0.3-0.7%. The sex ratio differs in different populations and may be influenced by interpretation of symptoms, with negative symptoms emphasized in males while mood symptoms may be emphasized in females. Whether these differences represent variations in the disorder itself or variations in expectations is not yet clear. Expression of symptoms may also be influenced by cultural or religious practices, such as hallucinations of hearing “god's voice” or delusions of having supernatural powers. Schizophrenia is comorbid with substance use disorders, though substance use may represent a consequence rather than a cause of schizophrenic symptoms. Approximately 50% of patients with schizophrenia use tobacco, suggesting it may be a type of self-medication for managing some symptoms. Some researchers have suggested that schizophrenia could be classified as a neurodevelopmental disorder, with the possibility that brain development during childhood is responsible for the symptoms which emerge later (most frequently in adolescence or early adulthood).

Despite depictions in popular culture, the vast majority of schizophrenia sufferers are not aggressive or violent and they are far more likely to be victims of violence or mistreatment rather than perpetrators. Schizophrenia carries an elevated risk of suicide; nearly 20% of sufferers will attempt suicide and 5-6% will complete suicide.

Pica (from the Latin for “magpie”, a reference to the bird's indiscriminate eating) refers to repeated and persistent (at least one month) eating of nonfood substances with little or no nutritional value. The minimum age for diagnosis is 2 years (so the fact that babies try to put everything in their mouths doesn't count) and the eating behavior must be “developmentally inappropriate”. In addition, the nonfood items must not be part of a culturally supported practice with spiritual, medicinal, or social value, such as geophagia (earth-eating) by women in South Africa who believe consuming clay improves skin softness. Common items on the pica menu include paper, soap, cloth, hair, string, wool, soil, chalk, paint, gum, metal, pebbles, charcoal, ash, starch, and ice. Pica is often comorbid with autism spectrum disorder and intellectual disability.

Binge-eating disorder is a new addition to the DSM-5 as a separate eating disorder. Binge-eating refers to episodes of eating until uncomfortably full, feeling a lack of control over eating, and feeling disgusted, depressed, or guilty after, resulting in distress but without any inappropriate compensatory behaviors (such as vomiting, using laxatives, or exercising excessively). Binge-eating episodes are defined as eating an amount of food definitely larger than most individuals would eat in similar circumstances (so Thanksgiving doesn't count) and in a discrete period of time (such as 2 hours, rather than snacking all day). To warrant diagnosis of the disorder, episodes of binge-eating must occur at least once a week for at least 3 months. 12-month prevalence is estimated at about 1.6% for females and 0.8% for males.

The main symptom of anorexia nervosa is an intense fear of gaining weight or becoming fat, which leads to extreme restriction of energy intake. This can result in very low body weight, with severe cases showing a BMI below 15 (a BMI of 18.5 is considered the lower limit for “normal” body weight in adults). Though the word anorexia comes from the Greek for “without appetite”, sufferers do still experience hunger. Other symptoms include disturbed experience of body shape or weight (believing they are fat or overweight despite clear evidence to the contrary), depressed mood, social withdrawal, insomnia, low sex drive, and loss of bone mineral density. Some women also experience amenhorrhea, or cessation of their menstrual cycle.

Anorexia nervosa can be further specified as restricting type or binge-eating/purging type. The binge-eating/purging type is differentiated from bulimia nervosa based on body weight, as a diagnosis for bulimia nervosa occurs within the normal body weight range, while anorexia nervosa is diagnosed if bingeing and purging is accompanied by low body weight.

12-month prevalence of anorexia nervosa is estimated to be about 0.4% for young women. Anorexia nervosa overwhelmingly affects females, with a female to male ratio of 10:1. Anorexia nervosa is comorbid with bipolar disorder as well as depressive and anxiety disorders. Considered one of the deadliest of all mental illnesses, anorexia diagnosis carries a roughly 6-fold increase in mortality due to consequences of starvation in addition to an elevated risk of suicide, which accounts for 1 in 5 anorexia deaths.

Bulimia nervosa is an eating disorder characterized by binge-eating followed by inappropriate compensatory behaviors, such as vomiting, fasting, using laxatives, diuretics, or medications, or excessive exercise at least once a week for at least 3 months. Individuals with bulimia nervosa often have negative self-evaluations based on their body shape and weight and negative emotions often precede episodes of binge-eating, during which sufferers feel they cannot control their behavior. Unlike the low body weight of anorexia nervosa, bulimia nervosa is associated with body weight that is normal to overweight. 12-month prevalence is estimated to be 1-1.5%, mostly in young females, with a female to male ratio of 10:1. Depressive symptoms and mood disturbance are also common, as well as substance use, particularly the use of stimulants in an attempt to control appetite and weight.

The primary symptom of major depressive disorder is a depressed mood most of the day, every day, for at least a two week period. In addition to depressed mood, sufferers also experience decreased interest or pleasure in most activities (anhedonia), and may also show changes in appetite (and body weight) and sleep disturbances such as hypersomnia, sleeping for long periods of time, or insomnia, which often occurs in the form of early awakening followed by inability to return to sleep despite feeling tired. Many sufferers also experience fatigue and a slowing of motor activity, referred to as psychomotor retardation. Cognitive symptoms include thoughts of worthlessness (which may be extreme enough to be considered delusional – such as “my brain is rotting” or “I am the worst person in the world”), difficulty concentrating and making decisions, and in some cases, suicidal thoughts.

Sufferers may also find themselves persistently and repetitively thinking about minor past failures or how depressed they currently feel, and this rumination may worsen symptoms and feelings of helplessness. As Sylvia Plath's character Esther Greenwood described, "Wherever I sat — on the deck of a ship or at a street cafe in Paris or Bangkok — I would be sitting under the same glass bell jar, stewing in my own sour air." Some patients with major depressive disorder report feeling “blah” or having no feelings, while others may emphasize somatic symptoms such as aches, pains, or fatigue that occurs without any physical exertion.

The estimated 12-month prevalence of major depressive disorder is 7% and it is 3 times more common in young adults (18-29) than those over 60. The lifetime prevalence of depression has been estimated to be as high as 7-12% in males and 20-25% in females (Kessler, 2005). Each major depressive episode increases the odds of a subsequent episode; 50-60% of patients who experience one episode will experience a second, of those 70% will experience a third, and of those 90% will experience a fourth.Women with depression are more likely to attempt suicide than males, though males are more likely to complete suicide. This is because males tend to chose methods such as jumping from a building or using a firearm, while females are more likely to use methods with greater odds of rescue, such as pill ingestion or wrist-cutting. It's worth noting that when depression is extreme, risk of suicide is low. Suicide risk actually rises as severely depressed patients start feeling better. In the depths of depression, patients may lack the energy or motivation to carry out potential suicide plans but a dangerous combination occurs when fatigue fades and suicidal thoughts remain.

Episodes of depression may be further specified if they occur in certain patterns such as a seasonal pattern (also known as seasonal affective disorder) in which episodes occur during fall or winter and may be related to decreased levels of sunlight. Peripartum onset (commonly called postpartum depression though it often begins before childbirth) refers to depressive episodes in women which occur during pregnancy or in the 4 weeks following childbirth and may be related to hormonal changes. Peripartum depression may also include panic attacks, agitation, and in extreme cases, desire to harm oneself or the newborn child.

While major depressive disorder tends to occur in episodes of depression which come and go, persistent depressive disorder (formerly dysthymia) refers to a depressed mood most of the day, more days than not, for at least 2 years. 12-month prevalence is estimated to be about 0.5% and it's possible to have persistent depressive disorder coupled with periods of major depressive disorder, specified as persistent depressive disorder with major depressive episodes (which was formerly referred to as double depression).

As the name suggests, disorders in this category are characterized by two extremes (or poles) of behavior: depressive episodes and manic episodes. Previously classed as “mood disorders” (a category that is no longer in the DSM-5), bipolar disorders now have their own category. Part of the reason for this re-categorization is that some extremes of behavior seen in these disorders do not involve mood.

Bipolar I disorder refers to having (not necessarily alternating) manic episodes and major depressive episodes. A manic episode is a period of time lasting at least one week, most of the day, every day, characterized by inflated self-esteem, grandiosity, decreased need for sleep (such as 3 hours/night), increased goal-directed activities as well as behaviors with potential painful consequences (buying sprees, sexual promiscuity, foolish investments), and talkativeness, which often shows flight of ideas, abruptly switching from one topic to another.

Diagnosis of a major depressive episode lasting at least 2 weeks follows the same criteria listed previously for major depressive disorder.

Kay Redfield Jamison, an expert on bipolar disorder, has written a number of popular books on the disorder and her own personal experiences suffering from it are described in “An Unquiet Mind”. The term “bipolar” was introduced in the DSM-IV to replace the previous name “manic-depressive disorder”, though Jamison has criticized the newer term for downplaying the existence of mixed states: periods of dark depression and simultaneous agitation, energy, and aggression.

12-month prevalence for bipolar I is 0.6% and it is slightly more common in males, with a male/female ratio of 1.1:1. The mean age of onset is 18. Bipolar I carries a risk of suicide which is 15x greater than that for the general population. Approximately 25% of all completed suicides are by bipolar I patients.

Bipolar II disorder is a combination of major depressive episodes and hypomanic episodes. Hypomanic episodes are less extreme than manic episodes, last for at least 4 days, and are not severe enough to cause social or occupational impairment. Bipolar II has a 12-month prevalence rate of about 0.8% in the United States (0.3% internationally) with usual age of onset during the mid-20s.

Because bipolar II often begins with a depressive episode, misdiagnosis as major depressive disorder is possible until the emergence of a hypomanic episode. About 5-15% of those diagnosed with bipolar II later experience a full-blown manic episode, which results in a diagnosis change to bipolar I. Misdiagnosis of depression for bipolar I or bipolar II is dangerous because antidepressant drugs can actually trigger manic episodes. Suicide risk for bipolar II is also quite high, and roughly 1 in 3 sufferers attempt suicide.

In addition to bipolar I and bipolar II, this category includes cyclothymic disorder, which refers to chronic fluctuating mood disturbances with periods of hypomanic and depressive episodes which are not frequent, severe, or long-lasting enough to fully meet the criteria for a bipolar diagnosis.

A personality disorder indicates a pattern of behavior beginning around adolescence or early adulthood which differs from cultural expectations, is resistant to change and stable across time and situations, and which causes significant distress or impairment. The DSM-5 recognizes 10 distinct personality disorders which can only be diagnosed after the age of 18 and are organized into 3 different clusters based on their similarities.

Cluster A refers to personalities which are generally considered to be odd or eccentric, Cluster B refers to those which are considered dramatic, emotional, or erratic, and Cluster C refers to those which are anxious or fearful. One may also be diagnosed with a personality change due to physiological effects from another medical condition (such as brain damage) or have traits of several personality disorders but not meet full criteria for a specific disorder, diagnosed as an unspecified personality disorder.

In the chapter on personality, we saw the complexity of accurately measuring personality traits, and we should keep this in mind when considering personality disorders. We may also wonder if calling some traits disorders is really just a way of labeling people with personality traits we don't like. At what point does narcissism stop just being an annoying trait and become a disorder?

Prevalence of personality disorders varies by cluster, and the prevalence estimate for disorders in cluster A is about 5.7%, cluster B is 1.5%, and cluster C is 6%. This represents an overall prevalence estimate of about 9.1% for any personality disorder, though this estimate includes the co-occurence of more than one personality disorder in the same patient.

If you've read Susanna Kaysen's memoir Girl, interrupted (or you've seen the film starring Winona Ryder and Angelina Jolie), borderline personality disorderborderline personality disorderA personality disorder marked by instability in relationships, self-image, and emotion, and intense fear of abandonment. was the diagnosis that Kaysen received upon her entrance to McLean hospital, where she stayed for 18 months in 1967.

Since we don't have a chapter dedicated to criminal psychology in this book (as it is not covered in most introductory classes), I thought I'd take a moment to point out the relationship between antisocial personality disorderantisocial personality disorderA personality disorder characterized by persistent violation of others' rights, deceitfulness, and lack of remorse., psychopathy and sociopathy. These terms have a great deal in common, and this is partly because the term psychopathy was used in early editions of the DSM but was replaced by antisocial personality disorder starting with the DSM-III. Adding to the confusion is the term sociopath, which is used interchangeably with psychopath by many, but not all, psychiatrists, criminologists, and forensic psychologists. Some prefer to use the term sociopath to emphasize those who are less able to mask their disregard for others and whose antisocial behaviors seem to stem from environment rather than genes but this is certainly still up for debate. Antisocial personality disorder uses the diagnostic criteria of the DSM-5 while psychopathy is often diagnosed using the Psychopathy Checklist – Revised (PCL-R), a 20-item scale developed by Robert Hare. While most psychopaths will also meet the criteria for antisocial personality disorder, it's possible (and fairly common) to have a diagnosis of antisocial personality disorder without meeting the PCL-R criteria for psychopathy. Since personality disorders aren't diagnosed until age 18, those under 18 showing cruelty, violation of the rights of others, and lack of guilt and empathy may be diagnosed with conduct disorder.

The DSM-5 also has a category for neurocognitive disorders which include Alzheimer's Disease, Traumatic Brain Injury (TBI), Parkinson's Disease, and prion-related diseases, which result from the accumulation of misfolded proteins known as prions (pronounced pree-ons) which damage brain cells (diseases include Creutzfeldt-Jakob disease, Kuru, and fatal familial insomnia). While the core focus of diagnosis for these disorders is on cognitive deficits, these disorders are somewhat unique in that several of them have clear biological markers that can be identified through brain scans and genetic testing.

The DSM-5 also has a category for 8 paraphilic disorders (from the Greek para - “abnormal” and philos - “fondness”), which refer to intense, persistent sexual interests which are not considered to be normal. These include voyeuristic disorder, exhibitionistic disorder (showing one's genitals), frotteuristic disorder (touching or rubbing against a non-consenting individual), sexual masochism disorder, sexual sadism disorder, pedophilic disorder, transvestic disorder, and fetishistic disorders focused on specific body parts or inanimate objects.

Some behavioral symptoms of paraphilic disorders can be criminal offenses (such as exhibitionism, frotteurism, and pedophilia). Having a paraphilia does not necessarily mean diagnosis, and the paraphilia must also involve distress, which often comes from the potential harm to self or others that might occur from satisfying the paraphilia.