Interhemispheric transfer evaluation in multiple sclerosis

Patients suffering from Multiple Sclerosis (MS) have frequently been found to suffer from damage to callosal fibers. Investigations have shown that th is damage is associated with signs of hemisphere disconnections. The aim of our study was to provide evidence for the first signs of interhemispheric dysfunction in a mildly disabled MS population. Therefore, we explored whet her the Interhemispheric Transfer (IT) deficit is multi-modal and sought to differentiate two MS evolution forms, on the basis of an interhemispheric disconnection index. Twenty-two patients with relapsing-remitting form of M S (RRMS) and 14 chronic-progressive (CPMS) were compared with matched contr ols on four tasks: a tachistoscopic verbal and non-verbal decision task, a dichotic listening test, cross tactile finger localization and motor tappin g. No overall impairment was seen. The dichotic listening and lexical decis ion tasks were the most sensitive to MS. In addition, CPMS patients' IT was more impaired and was related to the severity of neurological impairment. The different sizes of the callosal fibers, which determine their vulnerabi lity, may explain the heterogeneity of transfer through the Corpus Callosum . Therefore, evaluation of IT may be of value as an index of evolution in M S.