Clinical Diagnosis and Classification Systems

To begin any type of treatment, the client/patient must be clearly diagnosed with a mental disorder. Clinical diagnosis is the process of using assessment data to determine if the pattern of symptoms the person presents with is consistent with the diagnostic criteria for a specific mental disorder set forth in an established classification system such as the DSM-5 or ICD-10 (both will be described shortly). Any diagnosis should have clinical utility, meaning it aids the mental health professional in determining the prognosis, the treatment plan, and possible outcomes of treatment (APA, 2013). Receiving a diagnosis does not necessarily mean the person requires treatment. This decision is made based upon how severe the symptoms are, the level of distress caused by the symptoms, symptom salience such as expressing suicidal ideation, risks and benefits of treatment, disability, and other factors (APA, 2013). Likewise, a patient may not meet full criteria for a diagnosis but require treatment nonetheless.

Symptoms that cluster together on a regular basis are called a syndrome. If they also follow the same, predictable course, we say that they are characteristic of a specific disorder. Classification systems for mental disorders provide mental health professionals with an agreed upon list of disorders falling in distinct categories for which there are clear descriptions and criteria for making a diagnosis. Distinct is the key word here. People experiencing delusions, hallucinations, disorganized speech, catatonia, and/or negative symptoms are different from people presenting with a primary clinical deficit in cognitive functioning that is not developmental in nature but has been acquired (i.e. they have shown a decline in cognitive functioning over time). The former would likely be diagnosed with a schizophrenia spectrum disorder while the latter likely has a neurocognitive disorder (NCD). The latter can be further distinguished from neurodevelopmental disorders which manifest early in development and involve developmental deficits that cause impairments in social, academic, or occupational functioning (APA, 2013). These three disorder groups or categories can be clearly distinguished from one another. Classification systems also permit the gathering of statistics for the purpose of determining incidence and prevalence rates, they facilitate research on the etiology and treatment of disorders, and they conform to the requirements of insurance companies for the payment of claims.

The most widely used classification system in the United States and Canada is the Diagnostic and Statistical Manual of Mental Disorders currently in its 5th edition and produced by the American Psychiatric Association (APA, 2013). Alternatively, the World Health Organization (WHO) produces the International Statistical Classification of Diseases and Related Health Problems (ICD) currently in its 10th edition with an 11th edition expected to be published in 2018. We will begin by discussing the DSM and then move to the ICD.

The DSM Classification System

A Brief History of the DSM

The DSM 5 was published in 2013 and took the place of the DSM IV-TR (TR means Text Revision; published in 2000) but the history of the DSM goes back to 1844 when the American Psychiatric Association published a predecessor of the DSM which was a “statistical classification of institutionalized mental patients” and “…was designed to improve communication about the types of patients cared for in these hospitals” (APA, 2013, p. 6). However, the first official version of the DSM was not published until 1952. The DSM evolved through four subsequent editions after World War II into a diagnostic classification system to be used by psychiatrists and physicians, but also other mental health professionals. The Herculean task of revising the DSM IV-TR began in 1999 when the APA embarked upon an evaluation of the strengths and weaknesses of the DSM in coordination with the World Health Organization (WHO) Division of Mental Health, the World Psychiatric Association, and the National Institute of Mental Health (NIMH). This resulted in the publication of a monograph in 2002 called, A Research Agenda for DSM-V. From 2003 to 2008, the APA, WHO, NIMH, the National Institute on Drug Abuse (NIDA), and the National Institute on Alcoholism and Alcohol Abuse (NIAAA) convened 13 international DSM-5 research planning conferences, “to review the world literature in specific diagnostic areas to prepare for revisions in developing both DSM-5 and the International Classification of Disease, 11th Revision (ICD-11)” (APA, 2013).

After the naming of a DSM-5 Task Force Chair and Vice-Chair in 2006, task force members were selected and approved by 2007 and workgroup members were approved in 2008. What resulted from this was an intensive process of “conducting literature reviews and secondary analyses, publishing research reports in scientific journals, developing draft diagnostic criteria, posting preliminary drafts on the DSM-5 Web site for public comment, presenting preliminary findings at professional meetings, performing field trials, and revisiting criteria and text”(APA, 2013).

What resulted was a “common language for communication between clinicians about the diagnosis of disorders” along with a realization that the criteria and disorders contained within were based on current research and may undergo modification with new evidence gathered (APA, 2013). Additionally, some disorders were not included within the main body of the document because they did not have the scientific evidence to support their widespread clinical use, but were included in Section III under “Conditions for Further Study” to “highlight the evolution and direction of scientific advances in these areas to stimulate further research” (APA, 2013).

Elements of a Diagnosis

The DSM 5 states that the following make up the key elements of a diagnosis (APA, 2013):

• Diagnostic Criteria and Descriptors – Diagnostic criteria are the guidelines for making a diagnosis. When the full criteria are met, mental health professionals can add severity and course specifiers to indicate the patient’s current presentation. If the full criteria are not met, designators such as “other specified” or “unspecified” can be used. If applicable, an indication of severity (mild, moderate, severe, or extreme), descriptive features, and course (type of remission – partial or full – or recurrent) can be provided with the diagnosis. The final diagnosis is based on the clinical interview, text descriptions, criteria, and clinical judgment.
• Subtypes and Specifiers – Since the same disorder can be manifested in different ways in different individuals the DSM uses subtypes and specifiers to better characterize an individual’s disorder. Subtypes denote “mutually exclusive and jointly exhaustive phenomenological subgroupings within a diagnosis” (APA, 2013). For example, non-rapid eye movement sleep arousal disorders can have either a sleepwalking or sleep terror type. Enuresis is nocturnal only, diurnal only, or both. Specifiers are not mutually exclusive or jointly exhaustive and so more than one specifier can be given. For instance, binge eating disorder has remission and severity specifiers. Major depressive disorder has a wide range of specifiers that can be used to characterize the severity, course, or symptom clusters. Again the fundamental distinction between subtypes and specifiers is that there can be only one subtype but multiple specifiers.
• Principle Diagnosis – A principal diagnosis is used when more than one diagnosis is given for an individual (when an individual has comorbid disorders). The principal diagnosis is the reason for the admission in an inpatient setting or the reason for a visit resulting in ambulatory care medical services in outpatient settings. The principal diagnosis is generally the main focus of treatment.
• Provisional Diagnosis – If not enough information is available for a mental health professional to make a definitive diagnosis, but there is a strong presumption that the full criteria will be met with additional information or time, then the provisional specifier can be used. 

DSM-5 Disorder Categories

The DSM-5 includes the following categories of disorders:

Table 1.1. DSM-5 Classification System of Mental Disorders

The ICD-11

In 1893, the International Statistical Institute adopted the International List of Causes of Death which was the first edition of the ICD. The World Health Organization was entrusted with the development of the ICD in 1948 and published the 6th version (ICD-6), which was the first version to include mental disorders. The ICD-11 was published in June 2018 and adopted by member states of WHO in June 2019. The WHO states:

ICD is the foundation for the identification of health trends and statistics globally, and the international standard for reporting diseases and health conditions. It is the diagnostic classification standard for all clinical and research purposes. ICD defines the universe of diseases, disorders, injuries and other related health conditions, listed in a comprehensive, hierarchical fashion that allows for:

• easy storage, retrieval and analysis of health information for evidence-based decision-making;
• sharing and comparing health information between hospitals, regions, settings, and countries;
• and data comparisons in the same location across different time periods.

Source: http://www.who.int/classifications/icd/en/

The ICD lists many types of diseases and disorders and includes Chapter V: Mental and Behavioral Disorders. The list of mental disorders is broken down as follows:

• Organic, including symptomatic, mental disorders
• Mental and behavioral disorders due to psychoactive substance use
• Schizophrenia, schizotypal and delusional disorders
• Mood (affective) disorders
• Neurotic, stress-related and somatoform disorders
• Behavioral syndromes associated with physiological disturbances and physical factors
• Disorders of adult personality and behavior
• Mental retardation
• Disorders of psychological development
• Behavioral and emotional disorders with onset usually occurring in childhood and adolescence
• Unspecified mental disorder

Harmonization of DSM-5 and ICD-11

According to the DSM-5, there is an effort to harmonize the two classification systems so that there can be a more accurate collection of national health statistics and design of clinical trials, increased ability to replicate scientific findings across national boundaries and to rectify the lack of agreement between the DSM-IV and ICD-10 diagnoses. (APA, 2013). At time of publication of this text, however, this had not yet occurred.

References

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders. (5th ed.). Arlington, VA: American Psychiatric Publishing.

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders- Text revision (4th ed.). Washington, DC: Author.

Bridley, A., & Daffin, L. W. Jr. (2018). Diagnosing and Classifying Abnormal Behaviour. In C. Cuttler (Ed), Essentials of Abnormal Psychology. Washington State University. Retrieved from https://opentext.wsu.edu/abnormalpsychology/.