MAGNETIC STIMULATION OVER THE CEREBELLUM IN PATIENTS WITH ATAXIA

We studied 20 patients with ataxia caused by various disorders using m agnetic stimulation over the cerebellum. Results were compared with no rmal values found for 12 normal volunteers. In normal subjects, a magn etic stimulus over the cerebellum reduced the size of responses evoked by magnetic cortical stimulation when it preceded cortical stimulus b y 5, 6 and 7 ms. The grand average of the ratios of the areas of condi tioned responses at intervals of 5, 6 and 7 ms to those of control res ponses was designated the average area ratio (5-7 ms). Suppression of motor cortical excitability was reduced or absent in patients with a l esion in the cerebellum or cerebellothalamocortical pathway, but was n ormal in patients with a lesion in the afferent pathway to the cerebel lum. Normal suppression was observed in Fisher's syndrome. The average area ratio (5-7 ms) correlated well with the severity of ataxia in pa tients with degenerative late-onset ataxia. These results are consiste nt with those for electrical stimulation of the cerebellum reported pr eviously. We conclude that magnetic stimulation over the cerebellum pr oduces the same effect as electrical stimulation even in ataxic patien ts. This less painful method can be used clinically to clarify the pat homechanisms for ataxia. Two other clinical uses of this technique wer e that it revealed clinically undetectable cerebellar dysfunction in p atients whose extrapyramidal signs masked cerebellar signs, and that t he slow progression of ataxia could be followed quantitatively in pati ents with degenerative late-onset ataxia. (C) 1997 Elsevier Science Ir eland Ltd.