ICD-11 Revision of Mental Disorders: the Global Standard for Health Data, Clinical Documentation, and Statistical Aggregation

Mental health conditions in the World Health Organization (WHO) European Region affect more than 10% of the population, with 140,000 lives lost annually to suicide. Comorbidity with other diseases is high. However, basic mental health care is received by less than a third of patients. The COVID-19 pandemic has revealed the vulnerability of mental health services to disruptions and underscored the need to integrate mental health into response strategies. One of the flagship initiatives of the WHO European Programme of Work (EPW), 2020–2025: ‘United Action for Better Health in Europe’ is the establishment of a Mental Health Coalition at the European level. In this framework, reporting of health statistics using the International Classification of Diseases 11th Revision (ICD-11) will begin on 1st January 2022. Clinical utility, scientific rigour and wider cultural applicability were all of prime importance in the development of the ICD-11. The 11th Revision was the end product of the most extensive global, multilingual, multidisciplinary and participative process ever undertaken for this task, involving more than 15,000 experts from 155 countries, representing approximately 80% of the world’s population. With the adoption of the ICD-11 and the priority being given to mental health, new ideas based on the 30 years of research since the approval of the ICD-10 will be widely adopted and applied.

Even before the COVID-19 pandemic, the number of individuals with mental health conditions in the WHO European Region stood at over 110 million people, equivalent to more than 10% of the population.1,2 Moreover, 140,000 lives are lost each year in the Region to suicide, an unacceptably high figure that includes an increasing number of young people.3 Comorbidity with other non-communicable diseases (NCDs)4 and with communicable diseases such as tuberculosis5,6 and HIV7 is frequent, with mental health conditions sharing many of the same risk factors. Yet, out of all those in the European Region with the most common mental health conditions – depression and anxiety – the proportion receiving even basic care and support is at best a third, and as low as 5-10% in some European countries.1,2

The COVID-19 pandemic has revealed to an even greater extent the vulnerability of public health systems to health emergencies, particularly related to disruptions to mental health services. It has underscored the need to integrate mental health into present and future preparedness and response strategies.

The WHO European Programme of Work (EPW), 2020–2025: «United Action for Better Health in Europe», adopted in Copenhagen last September at the 70th session of the WHO Regional Committee for Europe, consists of four flagship initiatives that complement its three core priorities. They are intended as accelerators of change, mobilizing around critical issues that feature prominently on the Member States’ agendas. One of these four flagship initiatives is the establishment of a Mental Health Coalition at the European level. The upcoming World Health Assembly 2021 will devote considerable attention to mental health as a crucial part of a whole-of-society approach and universal health coverage, and to the WHO’s capacity to strengthen its work on mental health at global, regional and country levels, through the updated Mental Health Global Action Plan for 2013-2030.

With the ICD-11 approval by the World Health Assembly in May 2019, after more than a decade of intensive work, the transition from ICD-10 to the new ICD-11 for all Member States of the WHO has officially begun. Member States will be able to begin reporting health statistics using the ICD-11 as a framework from 1st January 2022.

The development of the ICD-11 chapter on Mental, Behavioural and Neurodevelopmental Disorders has been informed by several core principles, including clinical utility, international, transcultural and global applicability, and a multidisciplinary approach.8 Clinical utility was considered to be among the most important elements because it would determine the system’s acceptance by practitioners and therefore influence its role in treatment design and various administrative and social functions, including pensions and legal determinations.9

The Clinical Descriptions and Diagnostic Guidelines (CDDG) for ICD-11 Mental, Behavioural and Neurodevelopmental Disorders has followed this same approach based on a strong scientific methodology.10,11 It demanded collaboration among hundreds of international experts in specific fields and extensive collaboration with WHO Member States, funding agencies and professional and scientific societies. This was the most extensive global, multilingual, multidisciplinary and participative process ever undertaken for the development or the revision of a classification system for mental disorders. It included more than 15,000 experts from 155 countries, representing approximately 80% of the world’s population.12

Prime features of the development of the ICD-11 CDDG were: 1) the systematic gathering and distilling of data and information; 2) a lifespan approach rather than a cross-sectional conceptualization; 3) a focus on more pragmatic indices, including long-term comorbidity and disability. The sources and the final text of the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) were also carefully reviewed. While there are considerable differences between the ICD-11 and the DSM-5, these are substantive and intentional rather than accidental, unnecessary or unsupported by data.

Comorbidity is considered to be one of the most problematic issues in modern classification systems along with the excess fragmentation of nosological entities, sometimes referred to as the ‘atomization of psychopathology’.13,14 Some of the changes in the ICD-11 were made to decrease this artificial comorbidity, using broader categories like Bodily Distress Disorder and dimensional approaches, such as in Personality Disorder. A developmental approach to mental disorders has also unified the classification of child and adult presentations, with attention to presentations in older adults. This has facilitated the emphasis within the ICD-11 on a recovery-based viewpoint. Whereas the ICD-10 used a dichotomy between organic and non-organic mental disorders, such a rigid conceptualization was avoided in the 11th Revision.

A substantially new structure for the subclassification of mental disorders was followed (Table 1), which is also broadly compatible with the structure of the DSM-5. Regarding the disorders related to sexuality, paraphilic disorders (referred to as disorders of sexual preference in the ICD-10) were retained in the chapter on mental disorders. Sexual dysfunctions and gender incongruence (called Gender Identity Disorders in the ICD-10) were moved to a novel chapter specifically created for conditions related to sexual health.11,15

Several new nosological entities were created on the basis of data that had emerged since the approval of the ICD-10. Examples of such new entities are Bipolar II Disorder, Body Dysmorphic Disorder and Hoarding Disorder. Another unique characteristic is the adoption of a dimensional approach; in particular, it is notable that this was used not only for personality disorders but also for psychotic disorders. The extent to which this revolutionary change will be adopted by practitioners and its impact on reported data remain to be seen.

Table 1. ICD-11 Chapter on mental, behavioural and neurodevelopmental disorders: disorder groupings

Cultural applicability16-18 was also of prime importance and therefore flexibility in clinical judgement was allowed, facilitating the incorporation and utilization of local knowledge when it can aid in clinical decisions.

The ICD-11 represents the first revision of the ICD for nearly 30 years and reflects both an unprecedented effort and advances in methodological quality. With the end product now in place, the most difficult phase, that of rigorous implementation should begin, with a focus on training and on adoption of the ICD-11 in training and educational curricula.

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