BLINK REFLEX AND THE MASSETER INHIBITORY REFLEX IN PATIENTS WITH DYSTONIA

The excitatory and inhibitory interneuronal pathways in the brainstem are tested by examining the blink reflex and the masseter inhibitory r eflex, respectively. We studied the R2 component of the blink reflex a nd the SP2 component of the masseter inhibitory reflex and their recov ery cycle in 56 patients with various forms of dystonia. In patients w ith cranial, cervical, and generalized dystonia, but not in patients w ith extracranial segmental dystonia, the recovery cycle of both reflex es was enhanced. The recovery cycle of R2 and SP2 can demonstrate subc linical changes in excitability of brainstem interneurons. The degree of enhancement of the recovery cycles did not correlate, however, with the severity of clinical facial muscle impairment. In addition, the r ecovery cycles correlated positively with each other, showing that exc itatory as well as inhibitory interneuronal pathways in the brainstem are perturbed in dystonia. Study of the trigemino-facial and trigemino -trigeminal reflexes provides an objective tool for assessing function al abnormalities in dystonia.