The diagnostic classification systems

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There are two main classification systems used to diagnose mental disorders:

  • The Diagnostic and Statistical Manual of Mental Disorders, currently in its fifth edition (DSM-5-TR)[10].
  • The International Classification of Diseases, currently in its 11th revisions (ICD-11 [11]), which only recently came into effect on 1 January 2022 [11].

Although these systems are similar, there are a number of important differences. The disorder descriptions outlined in this chapter are based on the most recent edition of the DSM, released in March 2022 (DSM-5-TR [10]), but some references are made to the ICD-11 [11]. In particular, we have highlighted several key changes between the DSM-5-TR and ICD-11 that AOD workers should be aware of. It should be noted, however, that these are not the only differences between the two classification systems. It is also important to note that the disorder descriptions provided in the current versions of both the DSM and ICD vary to those provided in earlier versions, as each edition is updated to reflect evolutions in our understanding of disorders based on research. As such, AOD workers are encouraged to familiarise themselves with both the DSM-5-TR and ICD-11, in particular their uses, limitations, and recommendations regarding differential diagnosis (i.e., determining which symptoms are attributable to which disorder). The DSM-5-TR disorders described here have also been cross-referenced with the corresponding ICD-11 codes in Appendix D. Irrespective of any differences between classification systems, AOD workers should be mindful that the move towards a more dimensional approach of diagnosing mental health conditions emphasises the need for not only clinical judgement and expertise, but of central importance, the need to consider the whole person rather than a person presenting to treatment with a checklist of symptoms.

In these Guidelines we focus on 10 categories of disorder that are most commonly seen among people with AOD use disorders, grouped by DSM-5-TR and ICD-11 classification (Table 1).

Table 1: DSM-5-TR and ICD-11 classifications of most commonly co-occurring mental disorders among people with AOD use disorders

DSM-5-TR classification ICD-11 classification
Attention-deficit/hyperactivity disorder Attention deficit hyperactivity disorder
Schizophrenia spectrum and other psychotic disorders Schizophrenia or other primary psychotic disorders
Bipolar disorders Bipolar or related disorders
Depressive disorders Depressive disorders
Anxiety disorders Anxiety or fear-related disorders
Obsessive-compulsive disorder Obsessive-compulsive disorder
Trauma-related disorders Disorders specifically associated with stress
Feeding and eating disorders Feeding or eating disorders
Personality disorders Personality disorders and related traits or patterns
Substance-induced disorders

Substance-induced psychotic disorders

Substance-induced mood disorders

Substance-induced anxiety disorders

Substance-induced obsessive-compulsive disorder

There are, however, a number of other disorder types that people with AOD use disorders may experience. These include somatoform disorders, sleep disorders, and adjustment disorders. For further information on these disorders readers are referred to the DSM-5-TR and ICD-11.

It is also important to note that many symptoms of mental disorders mimic those of physical disorders. For example, although heart palpitations may be related to anxiety, they may be a symptom of a heart condition. Similarly, depressed mood may be a symptom of major depressive disorder, but may also be a symptom of hypothyroidism. For this reason, it is important that clients suspected of having a co-occurring mental health condition undergo a medical assessment to rule out the possibility of an underlying physical condition. This is particularly pertinent for people with advanced AOD use disorders, who may experience malnutrition or organ damage.

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