Masseter reflex in the study of spinocerebellar ataxia type 2 and type 3.

In this investigation we assess the utility of the masseter reflex for diagnostic purposes in autosomal dominant cerebellar ataxias. We studied the masseter reflex electrophysiologically in spinocerebellar ataxia type 2 (SCA2, 10 patients) and type 3 (SCA3/MJD, 13 patients). In SCA2, the masseter reflex was abnormal in 9 (90%) patients. In SCA3/MJD, the masseter reflex was normal in all 13 patients. Our findings suggest that the masseter reflex is a reliable test that provides additional data prior to molecular study in the differentiation between SCA2 and SCA3/MJD. Masseter reflex abnormalities in SCA2 patients could be better explained by dysfunction of the mesencephalic trigeminal nucleus/tract.