The lack of meaningful association between depression severity measures and neurocognitive performance.

Background: Neurocognitive deficits are common in depression, but most prior studies have not found strong associations between standard measures of symptom severity and the extent of these neurocognitive deficits. Diagnostic heterogeneity, or the lack of specific questions about neurocognition in these measures, may be undermining these associations.

Method: Neuropsychological performance was assessed via 10 tasks in a sample of 262 unmedicated patients with Major Depressive Disorder (MDD) and compared to that in healthy volunteers (n = 140), then correlated with (1) standard measures of depression severity including the Hamilton Depression Rating Scale and Beck Depression Inventory, (2) previously established, factor-analytically derived symptom factors that characterize the heterogeneity of these scales, and (3) a separate measure of cognitive complaint (Cognitive Failures Questionnaire) that was included to address the absence of specific questions about cognition in standard rating scales.

Results: Neurocognitive performance in these unmedicated MDD patients was not significantly associated with either total scores on the depression severity measures, any of their derived symptom factors, or the degree of subjective cognitive complaint - which itself was most strongly associated with mood disturbance.

Limitations: Depressed patients with the most prominent neurovegetative symptoms may be underrepresented in this sample.

Conclusions: Neurocognitive deficits were only weakly associated with standard depression symptom ratings, and not captured by self-report ratings of cognitive complaint. Neurocognitive deficits appear to be a separate symptom dimension that cannot be inferred from overall depression severity and require their own assessment, given that they have prognostic value for functional outcomes, suicide risk, and differential therapeutics.