Magnetic resonance imaging in tonic spasms of multiple sclerosis.

Two cases of unilateral tonic spasm are described in which high signal lesions typical of demyelination were identified on magnetic resonance imaging in the contralateral cerebral peduncle. Both cases exhibited subtle upper motoneuron signs on the side of the tonic spasms that were exacerbated immediately following an attack. In one case, functional impairment of contralateral corticospinal pathways was demonstrated by delayed central motor conduction. These cases support the view that tonic spasms in multiple sclerosis are due to lesions within the corticospinal tract.