Before we discuss the diagnosis of specific disorders, it is useful to review the criteria for mental disorders in general. To diagnose any mental disorder, the Diagnostic and Statistical Manual of Mental Disorders, Edition 5 (DSM-5; APA, 2013) states the symptoms must cause a person significant distress or impairment. This overarching criterion applies to obsessive-compulsive and related disorders. Likewise, behavior must be evaluated within a developmental and cultural context. For instance, it is developmentally normal for adolescents to become quite preoccupied with their appearance. This does not necessarily mean they have body dysmorphic disorder. Similarly, there is variation among cultures about the type and intensity of religious rituals. Therefore, the fact someone prays several times a day, at specific times of day, with specific objects of religious significance, and becomes highly upset if any part of this ritual is disrupted, does not necessarily indicate an obsessive-compulsive disorder
So, what does distinguish a mental disorder from healthy behavior? The duration, frequency, and intensity of symptoms are evaluated within a developmental and cultural framework. Symptoms must be excessive and persistent. They must be highly distressing and/or cause significant problems in social, educational, or occupational functioning. These symptoms exceed the usual norms for people of a similar age and culture. Therefore, just because someone is experiencing some obsessive or compulsive symptoms, it does not necessarily mean they meet the requirements for a mental disorder. We begin to consider the possibility of a disorder when someone's symptoms start to interfere with their ability to have meaningful social relationships, and/or when the symptoms cause problems or difficulties at work or at school.
The disorders included in the obsessive-compulsive and related disorders category (OCRDs) are characterized by obsessions and/or compulsions. Obsessions are repetitive, unwanted, and intrusive thoughts. Compulsions are repetitive behaviors a person feels driven to perform. Attempts to block or prevent obsessions and compulsions cause a marked increase in distress. This distress is usually manifested as a high degree of anxiety. Some disorders in the OCRDs category may be more aptly described as an unrelenting preoccupation, or excessive concern, rather than an obsession in the traditional sense.
The obsessional thoughts, preoccupation, and responses to those thoughts, are often irrational and/or reflect rather gross perceptual distortions. Sometimes people with these disorders recognize their thoughts and behavioral responses are not sensible. In other cases, they do not. These different degrees of insight have important implications regarding the selection and success of treatment. Generally, the greater the degree of insight, the better the prognosis for a successful recovery.
In certain disorders, insight is such an important factor that clinicians evaluate and record the degree of insight as part of the diagnostic process. This is called a specifier. Some disorders also have various sub-types that can be recorded. This extra information helps treatment professionals to better manage and treat the disorder. Each disorder has its own respective group of specifiers or subtypes. Some have none. Where appropriate, these subtypes and specifiers will be discussed along with each disorder.
It is important to note the DSM-5 (APA, 2013) establishes a symptom criteria set for each disorder. A person must have a certain number of symptoms, from that set, in order to be diagnosed with that disorder. Because it is not necessary to have every symptom in the criteria set, people with the same disorder may not necessarily have the exact same symptoms. For instance, someone might obsess about germs as the primary symptom of OCD while another person may have intrusive sexual thoughts.