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 reflex, respectively. We studied the R2 component of the blink reflex and the SP2 component of the masseter inhibitory reflex and their recovery cycle in 56 patients with various forms of dystonia. In patients with cranial, cervical, and generalized dystonia, but not in patients with extracranial segmental dystonia, the recovery cycle of both reflexes was enhanced. The recovery cycle of R2 and SP2 can demonstrate subclinical 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 recovery cycles correlated positively with each other, showing that excitatory 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 functional abnormalities in dystonia.