Lesion load may predict long-term cognitive dysfunction in multiple sclerosis patients.

Background: Magnetic Resonance Imaging (MRI) techniques provided evidences into the understanding of cognitive impairment (CIm) in Multiple Sclerosis (MS).
Objectives: To investigate the role of white matter (WM) and gray matter (GM) in predicting long-term CIm in a cohort of MS patients.
Methods: 303 out of 597 patients participating in a previous multicenter clinical-MRI study were enrolled (49.4% were lost at follow-up). The following MRI parameters, expressed as fraction (f) of intracranial volume, were evaluated: cerebrospinal fluid (CSF-f), WM-f, GM-f and abnormal WM (AWM-f), a measure of lesion load. Nine years later, cognitive status was assessed in 241 patients using the Symbol Digit Modalities Test (SDMT), the Semantically Related Word List Test (SRWL), the Modified Card Sorting Test (MCST), and the Paced Auditory Serial Addition Test (PASAT). In particular, being SRWL a memory test, both immediate recall and delayed recall were evaluated. MCST scoring was calculated based on the number of categories, number of perseverative and non-perseverative errors.
Results: AWM-f was predictive of an impaired performance 9 years ahead in SDMT (OR 1.49, CI 1.12-1.97 p = 0.006), PASAT (OR 1.43, CI 1.14-1.80 p = 0.002), SRWL-immediate recall (OR 1.72 CI 1.35-2.20 p<0.001), SRWL-delayed recall (OR 1.61 CI 1.28-2.03 p<0.001), MCST-category (OR 1.52, CI 1.2-1.9 p<0.001), MCST-perseverative error(OR 1.51 CI 1.2-1.9 p = 0.001), MCST-non perseverative error (OR 1.26 CI 1.02-1.55 p = 0.032).
Conclusion: In our large MS cohort, focal WM damage appeared to be the most relevant predictor of the long-term cognitive outcome.