A longitudinal study of cognitive function in melancholic and non-melancholic subtypes of major depressive disorder

Abstract

Background: Research concerning cognition in depression has often yielded inconsistent findings. The presence of mixed melancholic and non-melancholic subtypes of major depressive disorder (MDD) in most previous research may explain some of the contradictory results (Hickie, 1996).

Methods: This longitudinal study compared the cognitive performance of people with melancholic (n=17) and non-melancholic (n=17) MDD admitted to one of two university hospitals. Participants received an extensive clinical and cognitive assessment at admission and again 3 months after recovery and discharge.

Results: Overall, participants with melancholia had selective memory deficits with broader impairment of executive control skills. Specifically, after correcting for depression severity, they performed more poorly on tests requiring memory acquisition, mental flexibility, set-shifting, selective attention, concept-formation and multi-tasking compared to those with non-melancholic depression. These deficits were present at both assessments suggesting that the increased initial severity of cognitive deficits for those with melancholia mean that they require a longer time to recovery.

Limitations: The clinical homogeneity of the study sample may underestimate the extent of cognitive impairment for those presenting with comorbid illness and/or significant drug/alcohol histories.

Conclusions: These findings indicate that the depressed group with melancholia have a distinctly different and more impaired cognitive profile to those without melancholic features and suggest that these clinical subtypes should be considered separately in future research concerning MDD. Furthermore, the melancholic group appears to require longer periods for cognitive recovery and this has implications for return to work and daily functioning following clinical discharge.