Depressive symptoms and fatigue as predictors of objective-subjective discrepancies in cognitive function in multiple sclerosis.

Objective: To examine the degree to which depressive symptoms and fatigue in individuals with multiple sclerosis (MS) are associated with discrepancies between subjective and objective cognitive impairment.

Methods: Ninety-nine adults with MS who were receiving care in a university-affiliated MS center completed the Patient Health Questionnaire-8 (PHQ-8), Fatigue Severity Scale (FSS), MS Neuropsychological Screening Questionnaire (MSNQ), and Brief International Cognitive Assessment for MS (BICAMS). Participants were classified as "Accurates," "Underestimators," or "Overestimators" based on discrepancies between their MSNQ (subjective) and BICAMS (objective) scores. Underestimators were individuals whose subjective scores were significantly worse than their objective scores. Overestimators exhibited the opposite profile.

Results: The PHQ-8 (r = 0.58) and FSS (r = 0.48) significantly correlated with the MSNQ, but not with the BICAMS (rs < 0.07). Underestimators (i.e., participants who underestimated their objective cognitive functioning) exhibited higher PHQ-8 and FSS scores compared to Accurates (ps < 0.01) and Overestimators (ps < 0.01). Optimal cut-scores of ≥6 on the PHQ-8 and ≥36 on the FSS provided fair accuracy (78% and 74%) for identifying Underestimators. Identification of Underestimators based on PHQ-8 and FSS scores was not moderated by any demographic or MS clinical variables.

Conclusions: In the presence of mild levels of depression or significant fatigue, subjective cognitive measures are unlikely to provide accurate estimates of objective cognitive functioning. Objective cognitive measures are required for accurate identification of cognitive impairment.