Impact of psychiatric and medical comorbidity on cognitive function in depression

Aim: The aim of the present study was to investigate the association between cognitive performance and psychiatric and medical comorbidity in major depression. Methods: The present study evaluated the cognitive performance of patients (n = 96) diagnosed with a major depressive episode in relation to the presence of medical and/or psychiatric comorbidity. Participants were assessed clinically and cognitively using the Mini International Neuropsychiatric Interview and Repeatable Battery for the Assessment of Neuropsychological Status. Four groups of comorbidity were categorized: (i) no comorbidity, (ii) medical comorbidity; (iii) psychiatric comorbidity; and (iv) both medical and psychiatric comorbidity, and subsequently analyzed for differences across six cognitive domains: immediate memory, visuospatial, language, attention, delayed memory, and total score. Results: Only 20.8% of the participants did not have a comorbidity of any kind, while psychiatric comorbidities (67.7%) were more frequent than medical comorbidities (39.6%). Education and severity of depressive symptoms negatively influenced cognitive performance. Psychiatric comorbidity alone significantly decreased cognitive performance in the visuospatial/constructional and the language domains and the total score. In addition, increasing numbers of psychiatric comorbidities were related to worse cognitive performance. In contrast, medical illnesses alone had no negative impact on any of the domains of cognitive performance. Evidence was found for additive effects of medical and psychiatric comorbidities in depression on visuospatial/constructional cognitive abilities. Conclusion: The strongest predictor of poor cognitive performance in depression was psychiatric comorbidity. The assessment and treatment of cognitive dysfunction in depression should consider the relative impact of psychiatric comorbidity.