Surface electromyographic study of idiopathic cranial dystonia focused on the orbicularis oculi muscles.

We studied 115 Japanese patients with idiopathic cranial dystonia (Meige disease), using surface electromyography (EMG) focused on the orbicularis oculi muscles to classify the findings of the abnormal involuntary movements of this disease and to evaluate the pathophysiology of blepharospasm (BS). Surface EMGs at rest and at voluntary eyelid opening after eyelid closing were investigated. We found 62 (53.9%) patients exhibiting the overblinking type, 37 (32.2%) the tonic BS type, and 16 (13.9%) the normal type of behavior, considering the frequency of spontaneous blinking and presence of spasms. The present results suggest that BS is not a summation of blinking but a spatial and temporal extension of the orbicularis oculi muscle activity engaging in blinking, and the classification of the present study can support the investigation of the temporal characteristics of patients with this disease.