On the nature of memory disturbance in multiple sclerosis

Thirty-seven patients with multiple sclerosis (MS) were compared to 26 normal controls of equivalent age, education, and verbal intelligence on measures of verbal learning and memory (Digit Span and Supraspan, Brown-Peterson Distractor Task, Selective Reminding Test, Story Recall, and Free Verbal Recall) and verbal fluency (Letter and Animal Fluency). The MS patients exhibited deficits on measures of secondary (long-term) memory and verbal fluency, but performed normally on measures of primary (short-term) memory, recognition memory, and rate of forgetting from secondary memory. These results suggest that the memory disturbance in MS results primarily from an imparied ability to access information from secondary memory, while encoding and storage capacity is intact. Degree of memory impairment was unrelated to length of illness, severity of disability, or self-reported depression.