Official classification of mental illnesses began as early as 1763 and continued through the 18th and 19th centuries as various attempts have continued to classify disorders by categories, symptoms, and psychiatric diagnoses. Thus, classification for psychiatric disorders is also known as psychiatric taxonomy and serves as a critical tool for mental health professional in diagnosis, treatment, and research (Apter, 2019). The modern classification systems of ICD-10 and DSM-5 are inherently complex but have been purposefully developed and accepted by psychiatrists worldwide for practical applications using specific classification schemes. This paper will explore the modern systems of classification for psychiatric disorders and discuss their values and limitations.
The two primary established systems of psychiatric classification currently are the Diagnostic and Statistical Manuel of Mental Disorders (DSM) and the International Classification for Diseases (ICD). The DSM is used by the American Psychiatric Association prevalent in the United States and Canada and is the largest psychiatric professional organisation with 38,500 members worldwide. DSM was started in 1917, outlining symptoms for 21 disorders. A major paradigm shift occurred with DSM-3 in 1980 using a multiaxial system, using the clinical specificity of diagnostic criteria (American Psychiatric Association, n.d.a).
The latest version is DSM-5, published in 2013, which dropped the multiaxial system and inclusion of more disorders, including Autism Spectrum Disorder and gender dysphoria. The order of categories is based on aetiological similarities as well as using a polythetic system that lists symptoms, and diagnostic labels are assigned to patients based on whether these symptoms are exhibited (American Psychiatric Association, n.d.b)
The ICD includes all health disorders, not just psychiatric ones. It is used in over 100 countries by various health professionals as it was developed by the World Health Organisation, initially used to track morbidity and mortality. Over the years, the ICD was modified as well, making changes to the psychiatric disorders section. Since 1994, ICD-10 has been in use and represents the most updated and radically changed (from previous versions) of the manual. In ICD-10, disorders are arranged in groups by similarity, based on current understanding and standardised definitions of the disorder. The categories are also more expanded and are arranged to include related or coexisting syndromes (World Health Organization, n.d.).
ICD-11 coming into effect by 2022 further increases specificity and adds or changes disorders appropriately, such as not classifying transgender as a mental disorder and adding gaming disorder as a condition, among others (Apter, 2019).
Classifications have a wide variety of purposes, but the primary one can be attributed to the need for communication and standardisation of language among clinicians, researchers, and psychiatrists at the national and international levels in the area of mental health disorders. Classification allows for the establishment of defined nomenclature, creates a nosographical reference system to be applied in practice, and optimising research for homogeneity of samples and knowledge. In order to have a practical interest and application, classification systems must be reliable, valid, and accepted by a wide range of potential users (Lempérière, 1995).
In the field of psychiatry, which historically, and to this day, has many subjective elements and differences in perceptions, there has been increased efforts to improve methodological approaches to classification and categorisation as to ensure validity and homogenous standardisation. The classification systems define psychiatric disorders within the mental health care system, seeking to improve diagnostic validity (DSM) and clinical utility (ICD).
One of the primary values of classification systems, as they have significantly reduced international linguistic confusion and conceptual understanding regarding psychiatric disorders. Since the introduction of DSM and ICD, there has been a trajectory towards one common language for defining and conceptualising mental health disorders (van Heugten – van der Kloet & van Heugten, 2015).
In clinical use, the classification systems allow for more accurate diagnoses and provide a key tool for mental health and clinical professionals to conceptualise cases within the context of the unique traits and set of circumstances for the client. In turn, the standardisation and more accurate diagnosis are more likely to lead to appropriate and helpful treatment. Therapists can have the ability for concrete assessment of issues, and while diagnosis and treatment still remain an ‘art’ to some extent, the classification systems eliminate much of the guesswork. Most of the classification systems have recommendations for treatment based on the diagnostic criteria laid out in the manuals, while in the United States, DSM codes must be cited for insurance and billing purposes (Jewell et al., 2009).
Meanwhile, in research, the classification once again aids in standardisation of international research, ensuring that there is homogeneity among researchers and their publications, contributing to the practical aspects of psychiatry (“DSM-5 – pros and cons,” 2013).
Despite their values and benefits, the current classification systems of psychiatric disorders are inherently flawed, making them at times ineffective and other times, highly controversial among the professional and scientific community. One of the primary issues is that the classification systems provide very broad and unclear constructs that are operationally defined. While DSM-5 has emphasised diagnostic validity and ICD-11 focuses on clinical utility, there is both an overlap between the two, as well as interdependence – with clinical utility reliant on diagnostic validity. This creates somewhat of a closed loop as well as confusion in practical application (Stein et al., 2013).
There are also issues with reliability and validity present for many psychiatric disorders. Research is carried out on few groups of disorders, often with a highly Western bias, and many of the diagnoses in the DSM-5 manual for example, have not been tested. Field trials demonstrate low reliability with an overexaggerated emphasis on checklists of symptoms that do not accurately capture the complexity of mental illness.
The categorisation in both DSM-5 and ICD-11 is clunky as well, with categories not being mutually exclusive, and there is often overlap of symptoms and presentations. Finally, an issue that is most frequently mentioned among mental health professionals and researchers is that the classification systems fail to account for comorbidity. In mental illness, there are often demonstrations of multiple symptoms and the need for complex diagnoses – there is a presence of comorbidities. The high rates of comorbidity lead to nonspecific of both psychosocial and pharmacological treatments based on the current system which inherently questions the specificity of the disorders (Kapadia et al., 2020).
Discussion and Future Opportunities
There are obvious limitations to the current systems, which have led to the emergence of potential other approaches and dimensional models that could potentially be adapted into the major systems of DSM and ICD or become separate systems used by professionals. One of such systems is the Hierarchical Taxonomy of Psychopathology (HiTOP), which has the primary objective of providing an empirically based, fully dimensional organisation of psychopathology. The key is to subject the known diagnoses, syndromes, and symptoms to multivariate factor-analytic procedures (Hengartner & Lehmann, 2017).
The HiTOP premise is that psychopathology is hierarchically structured following almost a pyramid structure of domains. It also innovatively incorporates personality traits and can advance research on genetic vulnerabilities. Meanwhile, another potential model which has already begun to gain acceptance in some professional circles is the Research Domain Criteria (RDoC) developed by the National Institute of Mental Health (NIMH). RDoC focuses on the neurobiology and neuroscience of psychiatric disorders, viewing psychopathology in the context of deviations of fundamental functional systems. RDoC seeks to oppose the traditional DSM/ICD top-down approach and instead encourages a bottom-up approach, creating five neurobiological domains, each with its own constructs based on dysfunction in regular psychopathological systems (Hengartner & Lehmann, 2017).
It becomes evident that the modern mental health classification systems are imperfect but are constantly evolving to include current knowledge and understandings of disorders and psychiatry. There are a number of issues ranging from classification schema to lack of international standardisation to lack of considerations for certain contexts (i.e. primary care) and lack of inclusion of various mental health problems which are not characterised as a disorder (Klinkman et al., 2013).
The current systems formed over decades focused on consensus-driven diagnostic categories, with an emphasis on reliability and capacity to identify disorders via standardised checklists. However, it came short in connecting diagnostic groupings to underlying pathophysiology or treatments. The future direction of the classification system should focus on objectives of prioritising validating clinical entities and valuing new dimensions in developmental and neurobiological research. Classification of psychiatric disorders going forward should seek to break down historical barriers between clinical psychiatry, neurology, and psychology and promote new pathways to illness models (Hickie et al., 2013).
The classification systems of psychiatric disorders, DSM-5 and ICD-10, are fundamental organisational structures in modern psychiatry. They are created for the standardisation and identification of mental health disorders and to provide effective treatment. Classification systems use different approaches but are vital for diagnosis, treatment, and research. While offering much value in clinical settings, the systems are also inherently flawed, and there is much opportunity for new dimensions of classifications going forward. It is unknown if a perfect system can ever be created, but these classifications are consistently evolving to accommodate new knowledge and understanding in a rapidly evolving field.
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