Objective: The current investigation was designed to examine the influence of disease course on the specific patterns of acquisition and retrieval impairments in multiple sclerosis (MS).
Background: Recent investigations of learning and memory in MS have shown that many subjects have impaired verbal and visual new learning abilities, but normal long-term recall and recognition. However, heterogeneity in the learning and memory abilities of subjects has been documented. Some evidence in the literature suggests that this heterogeneity may be in part attributable to clinical variables, such as disease course.
Methods: Verbal and visual learning and memory tests, modified to equate MS groups with healthy controls on initial acquisition of information, were administered to 64 individuals with clinically definite MS (relapse-remitting = 21; primary progressive = 18; secondary progressive = 25), and to 20 healthy control participants. Recall and recognition performance then was evaluated at 30 minutes, at 90 minutes, and at 1 week for the verbal learning task, and at 30 minutes and at 90 minutes for the visual learning task.
Results: Results indicate that the two progressive forms of MS result in significantly greater deficits in regard to the acquisition of new verbal information, with the secondary progressive group showing a significantly higher failure rate in regard to meeting the learning criterion. Performance for recognition measures was not significantly different among groups, whereas recall performance of the primary progressive group was significantly below that of the control group and of the secondary progressive group. When testing new learning with visuospatial information, individuals with relapse-remitting MS and secondary progressive MS required more trials than control participants to learn the same amount of visual information. Visual recall and recognition performance did not differ between groups. No group differences in rates of forgetting for visuospatial material was observed after equating for acquisition.
Conclusions: Results of the current study indicate that the primary problem in MS with regard to memory functioning is in the acquisition of new information. Our findings support previous research showing verbal memory deficits with a progressive disease course and visuospatial memory deficits in relapse-remitting MS. However, the detailed analysis of new learning and memory performed in the current study indicated that the primary progressive group may be showing difficulty in their ability to use newly learned information. The pattern of new learning deficits observed between MS disease subtypes in the current study was determined to be unrelated to the duration of MS and to the physical severity of the disease. The degree of physical disability observed in patients with MS does not appear to be related to the degree of cognitive decline because of the distinct patterns and severity of memory dysfunction noted within each disease type, independent of physical disability.