A longitudinal study of callosal atrophy and interhemispheric dysfunction in relapsing-remitting multiple sclerosis

Objectives: To determine if callosal atrophy and interhemispheric dysfuncti on can be detected in the early stages of relapsing-remitting, multiple scl erosis (MS) and to evaluate their progression in relation to the disability and evolution of lesions seen on magnetic resonance imaging during a 5-yea r period. Methods: We compared 30 patients who had clinically definite early-onset re plasing-remitting MS and mild disability with control subjects. Regional an d segmental callosal size and extent of white matter abnormalities on magne tic resonance imaging, as well as performance on tasks exploring interhemis pheric transfer of motor, auditory, and sensory information were assessed. Patients with MS were evaluated at baseline and after 5 years. Physical dis ability was determined at both rimes using the Expanded Disability Status S cale score. Results: Patients with MS were seen with significant callosal atrophy and f unctional impairment of interhemispheric transfer at baseline that worsened during the 5-year study. A significant correlation was found between the m ag nitude of disability and the severity of morphological and functional ca llosal involvement at baseline. This association persisted at rear 5. Basel ine clinical characteristics such as age and prestudy relapse rate were unr elated to callosal size or interhemispheric performance. However, the numbe r of baseline T2-weighted lesions was correlated with callosal involvement and this relation persisted at year 5. Conclusion: Patients who had relapsing-remitting MS in the early stages of the disease and mild disability had significant callosal involvement that p rogressed over time. The relationship between disability, T2-weighted lesio ns load, and degree of morphological and functional callosal impairment con firm the potential value of using callosal dysfunction as a surrogate marke r of disease progression in MS.