Impact of information processing speed on episodic memory in multiple sclerosis: insights from survival analysis

Standardized episodic memory tests often impose time limits, obscuring whether poor performance in Multiple Sclerosis (MS) is due to cognitive or Information Processing Speed (IPS) deficits.

We assessed episodic memory performance on the Selective Reminding Test (SRT) in 157 persons with MS (pwMS) and 109 healthy controls using survival analysis to examine the number of trials required for two consecutive full recalls of a word list (SRT-goal). Survival analysis focuses on when a particular event occurs and appears appropriate to characterize the slow vs. rapid progression of learning in pwMS.

Results showed a significant difference among pwMS and control: the mean survival times decreased from 10.23 trials in patients to 8.52 trials in controls, indicating that controls achieved the task sooner than patients (p < .001). Among pwMS, those with preserved IPS reached the SRT-goal in a median of 9.71 trials, while those with impaired IPS took 10.67 trials on average (p < .001). Only 12.5% of IPS-impaired pwMS achieved the SRT goal, compared with 60% of those with preserved IPS. Comparing MS-subtypes, 60% of relapsing-remitting MS (RRMS) patients reached the SRT goal, whereas only 15.8% of secondary progressive MS (SPMS) and 15% of primary progressive MS (PPMS) patients did.

Survival analysis provides a complementary assessment of episodic memory to traditional paradigms and an innovative way to address slow-learning in MS. This study presents clinical lessons in the assessment of episodic memory and cognitive rehabilitation of pwMS.