Abnormal Long-Term Episodic Memory Profiles in Multiple Sclerosis?

Objective: Various verbal episodic memory impairments have been demonstrated in multiple sclerosis (MS), including encoding, retrieval and storage processes. Our clinical experiment suggests that a subset of MS patients may show another pattern with a distinctive evolution of performances after a 20 minutes delay (short-delay versus long-delay free recall). Methods: The current study assessed performances on the California Verbal Learning Test (CVLT) in MS with a special focus on evolution after delay to identify a subgroup of patients who may show a significant spontaneous improvement of long-delay free recall in comparison with short-delay free recall. Data from 52 MS patients were compared with those from 32 controls. Group analyses were conducted on classical scores. Individual MS performances were also analyzed, according to confidence intervals calculated using control data. Results: From individual analysis, memory comorbidities were frequently observed in a MS patient (17% of MS patients had only one impaired score, 17% had two or three scores, 27% had four or five scores and 38% had six or more). Regarding the evolution after delay, three profiles were highlighted: two classical (stable and worsening, i.e. storage deficit) and a third showing a significant degree of improvement. The improvement was significantly correlated with processing speed, primacy effect and sensitivity to retroactive interference only in this third MS subgroup. This benefit from delay was not related to the effect of semantic clustering. Conclusion: The current study suggests that a subgroup of MS patients might present a previously unreported abnormal long-term memory profile, in which an impaired short-term performance contrasts with a significant spontaneous improvement with delay. Previous studies have demonstrated the relevance of spaced learning in MS rehabilitation. If our results are corroborated in a larger sample, the CVLT may help to select patients that are likely to benefit from this temporal memory care.