Course in Diagnosis of Psychotic Disorders: Research Agenda

Résumé fourni par la source

This article examines a proposal to include course features in Diagnostic and Statistical Manual of Mental Disorders, sixth edition (DSM-6) for classification of psychotic disorders. We review current knowledge on this topic including course typologies proposed in the literature and empirical studies of illness course. We also consider whether types can capture variability in patient’s trajectories and discuss an alternative approach. Our review reveals that fundamental questions remain unanswered about course of psychotic disorders due to limitations of available research. We outline study designs needed to fill these gaps. Cohen and Ongur1 provided an incisive overview of the role illness course plays in the nosology of psychotic disorders. They made a compelling case that diagnostic systems limited to signs and symptoms are incomplete, and course patterns provide essential information not captured by symptom-based classifications. Furthermore, they proposed that diagnoses should include both symptom and course features. This proposal should be seriously considered in the upcoming DSM-6. The key question is what course patterns are established, and what remains to be learned about psychotic disorders. Premature deployment of diagnostic guidelines that do not correctly represent psychopathology can result in poor reliability, validity, and clinical utility.2–6 Arguably, reputation of prior editions of the Diagnostic and Statistical Manual of Mental Disorders suffered from inclusion of elements that proved to be incorrect, such as 10 personality disorders.4 Likewise, classic schizophrenia subtypes—paranoid, disorganized, catatonic, undifferentiated, and residual—offered such poor diagnostic stability, reliability, and validity that they were eliminated from Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5).7 As a particularly relevant example, DSM-5 uses illness course to distinguish persistent depressive disorder (PDD) from major depressive disorder (MDD), with 2 years of continuous depression required for PDD. PDD is distinct from MDD in etiology, outcome, and treatment response.8 Unfortunately, persistent type excludes cases of highly recurrent depression, although they are much more similar to PDD than to single-episode MDD.9,10 Empirical evidence indicates that a more valid typology would combine persistent and recurrent depression variants,11,12 which DSM-5 has not done. These examples caution against accepting face-valid typologies without empirical vetting, as alternative classifications may be much more valid and reliable.

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