Abstract: Objective To evaluate cognitive impairment in idiopathic demyelinating optic neuritis(IDON) and early stage of multiple sclerosis(MS). Methods A Consecutive group of 57 IDON patients were divided into 2 groups according to presence(IDON-A) or absence(IDON-N) of abnormal brain MRI. Twenty MS patients with the course of disease shorter than 5 years and minor physical disabilities(EDSS≤4 scores) were included as early MS group. A battery of neuropsychological tests were performed. Results Information processing speed, attention, verbal and spatial memory function in the IDON-A and MS groups were found worse than IDON-N and control groups(P=0.000, 0.001, 0.003, 0.018, 0.036). Executive function was statistically worse(P=0.000, 0.001, 0.036, 0.020) in IDON-A and MS groups than in control group, but not significantly different from IDON-N group. No significant differences were found between the IDON-N group and control group in almost all neuropsychological tests. Cognitive functions were weakly correlated with disease duration and EDSS scores. Conclusion Cognitive capacity damage, especially information processing speed, attention, verbal and spatial memory, executive function, can appear in very early stage of MS and even in clinical IDON stage.

Key words: optic neuritis, multiple sclerosis, cognitive dysfunction, neuropsychological tests