Subjective cognitive complaints relate to mild impairment of cognition in multiple sclerosis

Cognitive impairment is common in multiple sclerosis (MS), but cannot be reliably predicted by physical impairment. The negative impact of cognitive impairment makes early detection important, but subjective cognitive complaints may be attributed to depression. We examined the relationship between subjectively reported and objectively measured cognitive impairment in MS, adjusting for mood. A neuropsychological battery, the Multiple Sclerosis Functional Composite (MSFC), the Mental Health Inventory (MHI), the Modified Fatigue Impact Scale (MFIS), the Perceived Deficits Questionnaire (PDQ) were administered to 136 patients. Demographically-adjusted cognitive scores were calculated. Subjective impairment was defined as PDQ score-2 standard deviations above that for healthy persons. We modeled the relationship of cognitive scores (independent variables) to being subjectively impaired (dependent variable) using logistic regression. Immediate Memory (IM) and Processing Speed Index (PSI) scores were non-linearly related to subjective impairment. Patients were less likely to report subjective impairment if their PSI was normal (OR-0.11; 0.02-0.73) or markedly impaired (OR-0.17; 0.03-0.91), compared to mildly reduced PSI. In young patients decreases in IM were associated with increased subjective impairment (OR-1.25; 1.07-1.47). Subjectively reported impairment reflects subtle declines in PSI and IM independent of mood, fatigue, and physical impairment. Cognitive complaints should not be discounted due to depression.