Characterizing the phenotype of multiple sclerosis-associated depression in comparison with idiopathic major depression

Background: Depression is a common co-morbidity in patients with multiple sclerosis (MS). While somatic symptoms of MS correlate with depression levels, it is unclear whether the clinical presentation of MS-associated depression differs from patients with "idiopathic" major depressive disorder (MDD). Objective: To compare the clinical phenotype of depression among MS and idiopathic MDD patients. Methods: Mean relative contribution of individual Beck Depression Inventory-II (BDI-II) items was evaluated among n = 139 patients with relapsing-remitting MS and n = 85 MDD patients without somatic illness. Next, comparisons were repeated in n = 38 MS with clinically relevant depressive symptoms (BDI-II > 19) and n = 38 MDD patients matched for sex, age, and depression severity. Finally, the underlying construct of depression was compared across groups using confirmatory factor analysis (CFA). Results: Comparisons on a whole-group level produced the expected differences along somatic/non-somatic symptoms. However, when appropriately controlling for depression severity, age, and sex, only four items contributed differentially to BDI-II total scores in MS versus MDD. CFA suggested that the underlying depression construct is essentially identical in both groups. Conclusion: The clinical phenotype of "idiopathic" MDD and MS-associated depression appears similar when adequately examined. The relevance of these findings for psychotherapeutic approaches for MS-associated depression should be explored in future studies.