Dysthymia: clinical and external validity

This paper reviews current evidence in support of dysthymia as a sub-affective disorder that precedes major affective episodes, often by more than a decade. In cases beginning in childhood or adolescence, dysthymia is associated with high familial rates of mood disorders, and a recurrent pattern of superimposed major depression. At least two trait-like markers, sleep electro-encephalographic and thyroid axis abnormalities-similar to those in major affective disorder-have been reported. These data indicate a common pathophysiological substrate for both dysthymia and major depressive illness. All classes of antidepressants-most recently the serotonin re-uptake and the reversible MAO inhibitors-have been shown to be effective. Dysthymia was fairly recently included in the US(DSM) and WHO(ICD) classifications of mental disorders, because it characterises a prevalent clinical presentation of depression in both psychiatric and general medical settings. Patients given this diagnosis, instead of presenting with acute or full-blown episodes, often complain of low-grade chronic affective malaise for as long as they remember, yet without clinically observable signs of depression. As a result, questions have been raised about its validity, but from fundamentally opposite positions: (i) Is dysthymia better conceptualised as a personality (or neurotic) rather than mood disorder? (ii) Can dysthymia be distinguished from major depressive illness? This paper examines these and related questions along both clinical and external validating strategies, and in particular, the more recent accumulated evidence in support of the utility of the concept of dysthymia.