Psychopathy, sometimes considered synonymous with sociopathy, is traditionally defined as a personality disorder characterized by persistent antisocial behavior, impaired empathy and remorse, and bold, disinhibited, egotistical traits. Different conceptions of psychopathy have been used throughout history. These conceptions are only partly overlapping and may sometimes be contradictory.

Hervey M. Cleckley, an American psychiatrist, influenced the initial diagnostic criteria for antisocial personality reaction/disturbance in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM), as did American psychologist George E. Partridge. The DSM and "International Classification of Diseases" (ICD) subsequently introduced the diagnoses of antisocial personality disorder (ASPD) and dissocial personality disorder (DPD) respectively, stating that these diagnoses have been referred to (or include what is referred to) as psychopathy or sociopathy. The creation of ASPD and DPD was driven by the fact that many of the classic traits of psychopathy were impossible to measure objectively. Canadian psychologist Robert D. Hare later repopularized the construct of psychopathy in criminology with his Psychopathy Checklist.

Although no psychiatric or psychological organization has sanctioned a diagnosis titled "psychopathy", assessments of psychopathic characteristics are widely used in criminal justice settings in some nations, and may have important consequences for individuals. The study of psychopathy is an active field of research, and the term is also used by the general public, popular press, and in fictional portrayals. While the term is often employed in common usage along with the related but distinct "crazy", "insane", and "mentally ill", there is a distinction between those with psychosis and psychopathy.

Antisocial personality disorder is defined by a pervasive and persistent disregard for morals, social norms, and the rights and feelings of others. Individuals with this personality disorder will typically have no compunction in exploiting others in harmful ways for their own gain or pleasure and frequently manipulate and deceive other people, achieving this through wit and a facade of superficial charm or through intimidation and violence. They may display , think lowly and negatively of others, and lack remorse for their harmful actions and have a callous attitude to those they have harmed. Irresponsibility is a core characteristic of this disorder: they can have significant difficulties in maintaining stable employment as well as fulfilling their social and financial obligations, and people with this disorder often lead exploitative, unlawful, or parasitic lifestyles.

Those with antisocial personality disorder are often impulsive and reckless, failing to consider or disregarding the consequences of their actions. They may repeatedly disregard and jeopardize their own safety and the safety of others and place themselves and others in danger. They are often aggressive and hostile and display a disregulated temper and can lash out violently with provocation or frustration. Individuals are prone to substance abuse and addiction, and the abuse of various psychoactive substances is common in this population. These behaviors lead such individuals into frequent conflict with the law, and many people with ASPD have extensive histories of antisocial behavior and criminal infractions stemming back before adulthood.

Serious problems with interpersonal relationships are often seen in those with the disorder. Attachments and emotional bonds are weak, and interpersonal relationships often revolve around the manipulation, exploitation, and abuse of others. While they generally have no problems in establishing relationships, they may have difficulties in sustaining and maintaining them. Relationships with family members and relatives are often strained due to their behavior and the frequent problems that these individuals may get into.

Psychopathy is a personality disorder which has symptoms expressed over a wide range of settings. Socially, it expresses extensive callous and manipulative self-serving behaviors with no regard for others, and often is associated with repeated delinquency, crime and violence, but may also present itself in other, maybe even successful social settings. Mentally, impairments in processes related to affect (emotion) and cognition, particularly socially related mental processes, have been found in those with the disorder which suggest that their destructive social behavior is borne from these aberrant mental processes. Developmentally, symptoms of psychopathy have been identified in young children with conduct disorder, and is suggestive of at least a partial constitutional factor that influences its development.

While antisocial personality disorder is a mental disorder diagnosed in adulthood, it has its precedent in childhood. The DSM-5's criteria for ASPD require that the individual have conduct problems evident by the age of 15. Persistent antisocial behavior as well as a lack of regard for others in childhood and adolescence is known as conduct disorder and is the precursor of ASPD. About 25-40% of youths with conduct disorder will be diagnosed with ASPD in adulthood.

Conduct disorder (CD) is a disorder diagnosed in childhood that parallels the characteristics found in ASPD and is characterized by a repetitive and persistent pattern of behavior in which the basic rights of others or major age-appropriate norms are violated. Children with the disorder often display impulsive and aggressive behavior, may be callous and deceitful, and may repeatedly engage in petty crime such as stealing or vandalism or get into fights with other children and adults. This behavior is typically persistent and may be difficult to deter with threat or punishment. Attention deficit hyperactivity disorder (ADHD) is common in this population, and children with the disorder may also engage in substance abuse." CD is differentiated from oppositional defiant disorder (ODD) in that children with ODD do not commit aggressive or antisocial acts against other people, animals, and property, though many children diagnosed with ODD are subsequently rediagnosed with CD.

Two developmental courses for CD have been identified based on the age at which the symptoms become present. The first is known as the "childhood-onset type" and occurs when conduct disorder symptoms are present before the age of 10 years. This course is often linked to a more persistent life course and more pervasive behaviors, and children in this group express greater levels of ADHD symptoms, neuropsychological deficits, more academic problems, increased family dysfunction, and higher likelihood of aggression and violence. The second is known as the "adolescent-onset type" and occurs when conduct disorder develops after the age of 10 years. Compared to the childhood-onset type, less impairment in various cognitive and emotional functions are present, and the adolescent-onset variety may remit by adulthood. In addition to this differentiation, the DSM-5 provides a specifier for a callous and unemotional interpersonal style, which reflects characteristics seen in psychopathy and are believed to be a childhood precursor to this disorder. Compared to the adolescent-onset subtype, the childhood onset subtype, especially if callous and unemotional traits are present, tends to have a worse treatment outcome.

Typical deficiencies may include problems identifying, processing, describing, and working with one's own feelings, often marked by a lack of understanding of the feelings of others; difficulty distinguishing between feelings and the bodily sensations of emotional arousal; confusion of physical sensations often associated with emotions; few dreams or fantasies due to restricted imagination; and concrete, realistic, logical thinking, often to the exclusion of emotional responses to problems. Those who have alexithymia also report very logical and realistic dreams, such as going to the store or eating a meal. Clinical experience suggests it is the structural features of dreams more than the ability to recall them that best characterizes alexithymia.

Some alexithymic individuals may appear to contradict the above-mentioned characteristics because they can experience chronic dysphoria or manifest outbursts of crying or rage. However, questioning usually reveals that they are quite incapable of describing their feelings or appear confused by questions inquiring about specifics of feelings.

According to Henry Krystal, individuals suffering from alexithymia think in an operative way and may appear to be superadjusted to reality. In psychotherapy, however, a cognitive disturbance becomes apparent as patients tend to recount trivial, chronologically ordered actions, reactions, and events of daily life with monotonous detail. In general, these individuals lack imagination, intuition, empathy, and drive-fulfillment fantasy, especially in relation to objects. Instead, they seem oriented toward things and even treat themselves as robots. These problems seriously limit their responsiveness to psychoanalytic psychotherapy; psychosomatic illness or substance abuse is frequently exacerbated should these individuals enter psychotherapy.

A common misconception about alexithymia is that affected individuals are totally unable to express emotions verbally and that they may even fail to acknowledge that they experience emotions. Even before coining the term, Sifneos (1967) noted patients often mentioned things like anxiety or depression. The distinguishing factor was their inability to elaborate beyond a few limited adjectives such as "happy" or "unhappy" when describing these feelings. The core issue is that people with alexithymia have poorly differentiated emotions limiting their ability to distinguish and describe them to others. This contributes to the sense of emotional detachment from themselves and difficulty connecting with others, making alexithymia negatively associated with life satisfaction even when depression and other confounding factors are controlled for.

Alexithymia is considered to be a personality trait that places affected individuals at risk for other medical and psychiatric disorders while reducing the likelihood that these individuals will respond to conventional treatments for the other conditions. Alexithymia is not classified as a mental disorder in the fourth edition of the "Diagnostic and Statistical Manual of Mental Disorders". It is a dimensional personality trait that varies in severity from person to person. A person's alexithymia score can be measured with questionnaires such as the Toronto Alexithymia Scale (TAS-20), the Bermond-Vorst Alexithymia Questionnaire (BVAQ), the Online Alexithymia Questionnaire (OAQ-G2) or the Observer Alexithymia Scale (OAS). It is distinct from the psychiatric personality disorders, such as antisocial personality disorder or borderline personality disorder, with which it shares some characteristics, and is likewise distinct from the abnormal conditions of sociopathy or psychopathy.

Alexithymia is defined by:

1. difficulty identifying feelings and distinguishing between feelings and the bodily sensations of emotional arousal

2. difficulty describing feelings to other people

3. constricted imaginal processes, as evidenced by a scarcity of fantasies

4. a stimulus-bound, externally oriented cognitive style.

In studies of the general population the degree of alexithymia was found to be influenced by age, but not by gender; the rates of alexithymia in healthy controls have been found at: 8.3%; 4.7%; 8.9%; and 7%. Thus, several studies have reported that the prevalence rate of alexithymia is less than 10%. A less common finding suggests that there may be a higher prevalence of alexithymia amongst males than females, which may be accounted for by difficulties some males have with "describing feelings", but not by difficulties in "identifying feelings" in which males and females show similar abilities.

Psychologist R. Michael Bagby and psychiatrist Graeme J. Taylor have argued that the alexithymia construct is strongly related (negatively) to the concepts of psychological mindedness and emotional intelligence and there is "strong empirical support for alexithymia being a stable personality trait rather than just a consequence of psychological distress". Other opinions differ and can show evidence that it may be state-dependent.

Bagby and Taylor also suggest that there may be two kinds of alexithymia, "primary alexithymia" which is an enduring psychological trait that does not alter over time, and "secondary alexithymia" which is state-dependent and disappears after the evoking stressful situation has changed. These two manifestations of alexithymia are otherwise called "trait" or "state" alexithymia.

The onset of ORS may be sudden, where it usually follows after a precipitating event, or gradual.

Psychiatric co-morbidity in ORS is reported. Depression, which is often severe, may be a result of ORS, or may be pre-existing. Personality disorders, especially cluster C, and predominantly the avoidant type, may exist with ORS. bipolar disorder, schizophrenia, hypochondriasis, alcohol, drug abuse and obsessive compulsive disorder.

In ICD-10, the latest version of the International Statistical Classification of Diseases and Related Health Problems, somatization syndrome is described as:

ICD-10 also includes the following subgroups of somatization syndrome:

- Undifferentiated somatoform disorder

- Hypochondriasis

- Somatoform autonomic dysfunction

- Persistent somatoform pain disorder

- Other somatoform disorders, such ones predominated by dysmenorrhoea, dysphagia, pruritus and torticollis

- Somatoform disorder, unspecified

The DSM-IV-TR diagnostic criteria are:

- A history of somatic complaints over several years, starting prior to the age of 30.

- Such symptoms cannot be fully explained by a general medical condition or substance use or, when there is an associated medical condition, the impairments due to the somatic symptoms are more severe than generally expected.

- Complaints are not feigned as in malingering or factitious disorder.

The symptoms do not all have to occur at the same time, but may occur over the course of the disorder. A somatization disorder itself is chronic but fluctuating that rarely remits completely. A thorough physical examination of the specified areas of complaint is critical for somatization disorder diagnosis. Medical examination would provide object evidence of subjective complaints of the individual.

Diagnosis of somatization disorder is difficult because it is hard to determine to what degree psychological factors are exacerbating subjective feelings of pain. For instance, chronic pain is common in 30% of the U.S. population, making it difficult to determine whether or not the pain is due to predominately psychological factors.