Assessing cognitive performance in radiologically isolated syndrome

Background: Radiologically isolated syndrome (RIS) is defined as the occurrence of incidental brain MRI lesions suggestive of multiple sclerosis (MS) in otherwise healthy subjects without any signs or symptoms that could indicate to the disease. We evaluated cognitive performance in a cohort of RIS patients. Methods: A retrospective analysis of prospectively collected data from a population-based registry documenting demographic, clinical and imaging data of MS patients followed at our institution. Cognitive performance of subjects diagnosed with RIS according to Okuda's criteria was evaluated. Cognitive assessment was performed using MindStreams Global Assessment Battery to evaluate memory, executive function, visual spatial perception, verbal function, attention, information processing speed and motor skills, and compared to that of age- and education-matched healthy population. Results: Thirty patients diagnosed with RIS, mean age at first MRI, 34.3 +/- 1.9 years, and disease follow up ranging from 1 to 15 years, were included in the study. Eight patients (26.6%) converted to MS within 4.2 +/- 1.4 years. Cognitive performance was relatively preserved with a mean global cognitive score of 98.4 +/- 1.6 (median, 100), but all cognitive measurements were below the mean performance for age- and education-matched healthy population. Similar to MS patients, information processing speed was the most impaired cognitive function, mean 94.7 +/- 2.04, median 94. Cognitive performance did not differ between RIS patients who converted to MS and those who remained with sustained RIS. Conclusions: Cognitive performance in RIS subjects was below average for age- and education-matched norms. Information processing speed was the most impaired cognitive test. Cognitive performance of RIS subjects should be followed closely in order to identify any changes that may indicate conversion to MS.