Bipolar depression: prototypically melancholic in its clinical features

Abstract

Background: Numerous studies have considered whether bipolar depression is phenomenologically similar or different to unipolar depression. While there have been some relatively consistent individual features identified, no clear clinical phenotype has been defined for bipolar depression.

Methods: A self-report and clinician-rated measure of the Sydney Melancholia Prototype Index ('SMPI') was used to assess prototypic features of melancholic and non-melancholic depression in a sample of 901 patients clinically diagnosed with bipolar disorder or unipolar depression. The majority also completed a self-report (SDS) severity of depression measure, and provided current and historical data on depression, anxiety, global functioning and stressor severity.

Results: Comparative analyses favoured the SMPI-CR above the SMPI-SR measure in terms of discriminatory strengths. The previously determined SMPI-CR difference score cut-off of 4 or more for differentiating melancholic from non-melancholic depression was replicated in this larger sample. SMPI item and prototypic pattern analyses indicated that bipolar depression corresponded closely to unipolar melancholic depression in terms of clinical pattern features but not in regard to a number of socio-demographic, illness course and correlate variables. 'Atypical features' were common across bipolar and unipolar disorders, but somewhat more prevalent in bipolar disorder.

Limitations: There was no distinction made for the bipolar group between subtypes I and II, with the study simply comparing bipolar with unipolar disorders. The apparent superiority of the clinician-rated in comparison to the SMPI-SR measure may reflect a clinician judgement bias.

Conclusions: The SMPI-CR measure indicated that bipolar depression corresponds closely to melancholic depression in terms of its clinical phenotype.