Transdiagnostic approaches
The diagnostic paradigm is challenged by the fact that the processes that lead to mental health problems are transdiagnostic. Comorbidity is the rule and not the exception, an artefact that is due to categorical diagnostics. The categories are heterogeneous, with numerous ways of meeting the criteria, and the distinctions between them are hazy (15). The diagnostic criteria do not capture all of the important symptoms, and the pattern of symptoms varies (13, 14). Interventions are not guided by the diagnosis to any great extent (15).
In order to address this, transdiagnostic approaches either cut across traditional diagnostic boundaries or completely disregard them.
Epidemiological data suggest that mental disorders, which have been explained by higher-order factors (internalising, externalising and thought disorders), are best explained by a general psychopathological dimension: the p factor (16). High p scores are associated with life impairment, occurrence of familial mental disorders, developmental problems and impaired early-life brain function. The p factor explains why it is so difficult to find causes, consequences, biomarkers and treatments that are specific to individual mental disorders.
The National Institute of Mental Health considers DSM diagnoses a barrier to research. They write that the categories and criteria were formulated before the advent of modern neuroscience and are therefore unlikely to be valid (17). They add that this has hindered progress, and that we need a new approach to move forward. Research Domain Criteria is the institute's transdiagnostic alternative, which maps six domains instead of diagnostic categories.
Scientific studies of treatments tend to exclude patients with comorbidities. Treatments therefore often take place concurrently or sequentially for what the classification system defines as different disorders. Transdiagnostic therapy, which is not specific for particular diagnostic disorders, can be a simpler alternative.
Transdiagnostic therapy, which is not specific for particular diagnostic disorders, can be a simpler alternative
The scope of this article does not allow me to present the treatment research in detail. I give instead a few examples that illustrate the difficulty of combining the findings from treatment research with the idea that the treatment must be based on diagnostic categories.
In relation to psychotherapy, the extensive meta-analyses by Wampold and Imel (18) indicate that the efficacy of psychotherapy does not depend on adaptation to the diagnosis. The Unified Protocol for Transdiagnostic Treatment of Emotional Disorders uses the same protocol for depression, anxiety disorders and other disorders – instead of single-disorder protocols. One study found a similar effect, but a lower treatment dropout rate, when using the Unified Protocol than when using specific protocols for panic disorder, obsessive-compulsive disorder, social anxiety disorder and generalised anxiety disorder (19).
Treatment with psychotropic medications is rarely aimed at the diagnosis, but at the patient's signs and symptoms, such as anxiety or hallucinations (20). The link is weak between the diagnosis and the medication used. Few of those who use antipsychotics have ever been psychotic (21), and antidepressants are used for a great many mental health problems, with or without documentation of efficacy.