Time course of clinical and physiological effects of stimulation of the cerebellar surface in patients with spasticity.

A double-blind study of the short-term (12--48 hours) effects of cerebellar stimulation was performed on 11 selected patients with spasticity. Six of patients had a good clinical long-term response to chronic stimulation, four had a moderate response, and one had no response. Each patient received stimulation for two periods of 24 hours and was off stimulation for two periods of 24 hours. The periods were randomised over four consecutive days. Neither the patients nor the observer could distinguish between the days on stimulation and the days off stimulation. Simple tests of function of the upper limbs during stimulation, measurements of H responses, tonic vibration responses, vibration-induced suppression of H responses, stretch responses, and co-contraction, showed no differences between the four days. These results are contrasted with acute physiological changes seen in some patients during stimulation and also with the slow progressive improvement in clinical function that characterises the successful clinical response. It is suggested that lack of either acute or short-term changes in response to cerebellar stimulation does not predict the clinical outcome. If the strength of stimulation is changed, at least three days and preferably 10 days should be allowed for the effects to appear. The mechanisms responsible for the alleviation of spasticity are likely to be more complex than those mediating acute and reversible changes in reflex activity.