Sensory modulation of the blink reflex in patients with blepharospasm.

OBJECTIVE To measure the effects of a prepulse stimulus on the blink reflex responses elicited by an electrical stimulation of the supraorbital nerve in patients with blepharospasm with and without an effective sensory trick. DESIGN Blink reflexes to supraorbital nerve stimulation were preceded in test trials by a prepulse electrical stimulus to the third finger at various leading intervals. SETTING Ambulatory patients were treated regularly with botulinum toxin in the Neurology Department of the Hospital Clinic in Barcelona, Spain. SUBJECTS Seventeen patients with dystonic blepharospasm and 11 age-matched control subjects. Eight of the patients with dystonic blepharospasm used a sensory trick to alleviate spasms and 9 did not. MAIN OUTCOME MEASURES We measured amplitude of R1 and area of R2 responses elicited by the supraorbital electrical stimulus and determined the percentage of facilitation or inhibition induced by the prepulse. RESULTS Prepulse facilitation occurred in the R1 response at intervals of 60 to 100 milliseconds and was normal in all patients. Prepulse inhibition occurred in the R2 response at intervals between 50 and 200 milliseconds and was abnormally reduced in 11 patients (64.7%), including all 9 patients who did not use a sensory trick and 2 of the 8 patients who did use a sensory trick. There was a positive correlation between absence of sensory trick and abnormality of the prepulse effects (chi(2)= 23.8; P < .001). CONCLUSIONS Prepulse inhibition of the trigeminofacial reflex is abnormal in a percentage of patients with blepharospasm, and this abnormality occurs more frequently in patients who do not use a sensory trick. This sensory derangement may contribute to the maintenance of the dystonic spasms by reducing the amount of physiological gating from peripheral nerve inputs on trigeminofacial reflexes.