The nature of bipolar depression: implications for the definition of melancholia

Aim: To examine if melancholic depression is over-represented in those with ‘bipolar depression’ and, if confirmed, to use that phenomenon to assist the clinical definition of melancholia. Methods: We contrast 83 bipolar and 904 unipolar depressed patients on three melancholic sub-typing systems (DSM, Clinical and CORE system) and compare representation of their clinical depressive features. Results: By all three melancholic sub-typing systems, the bipolar patients were more likely to receive diagnoses of ‘melancholia’ and of psychotic depression. To the extent that this differential prevalence of depressive sub-types was reflected in varying patterns of clinical features, we so indirectly identified a set of items defining ‘melancholia’. By such a strategy, melancholia was most clearly distinguished by behaviourally-rated psychomotor disturbance. While a number of ‘endogeneity symptoms’ were significantly over-represented, logistic regression analyses refined the set to psychomotor disturbance (both as a symptom and as a sign) and pathological guilt. We also established a distinctly higher prevalence of bipolar depression in those where a refined diagnosis of melancholia was made. Conclusions: Bipolar depression appears to be more likely to be ‘melancholic’ in type, thus providing an indirect strategy for the clinical definition of melancholia.