Masseter reflex potentials in olivo-ponto-cerebellar atrophy.

We recorded masseter reflex potentials to examine the correlation between the masseter reflex and the muscle stretch reflexes of limbs in 19 patients with olivo-ponto-cerebellar atrophy (OPCA). The patients were subdivided into hyper- (n = 5), normo- (n = 7) and hypo- (n = 7) reflexia groups according to the degrees of the conventional deep tendon jerks in the upper limbs. The masseter reflex potentials, elicited by tapping the chin with a reflex hammer, were recorded from the bilateral masseters using a pair of surface electrodes. The latency of the potentials in the hyporeflexia was significantly longer than in the other groups, while the amplitude of those in the hyperreflexia group was significantly higher than in the other groups. These results indicate that in patients with OPCA the magnitude and latency of the masseter reflex correlates with the status of the muscle stretch reflexes of the limbs in contrast with Friedreich's ataxia where the masseter reflex has been reported to be normal or hyperactive despite hyporeflexia in the limbs.