Perioral reflexes in orofacial dyskinesia and spasmodic dysphonia.

In order to assess the clinical utility of trigemino-facial reflexes in lower facial muscles, we studied perioral reflexes to mechanical and electrical stimulation in 13 patients with spasmodic dysphonia and orofacial dyskinesia and in 7 healthy subjects. Mechanical stimulation of the upper lip of all patients and electrical stimulation of the infraorbital nerve of patients with orofacial dyskinesia elicited larger perioral reflexes than in controls. In the majority of patients, hyperexcitable perioral reflexes were accompanied by increased gain of the blink reflex. In 4 patients, however, trigemino-facial reflexes were enhanced selectively in either the perioral muscles or orbicularis oculi. Our findings suggest that the quantitative assessment of perioral reflexes may provide information about the excitability of brainstem interneurons in cranial dystonia that is complementary to blink reflex studies.