ELECTROMYOGRAPHY AND RECOVERY OF THE BLINK REFLEX IN INVOLUNTARY EYELID CLOSURE - A COMPARATIVE-STUDY

Electromyographic (EMG) activity of orbicularis oculi and levator palp ebrae muscles was recorded to study the origin of involuntary eyelid c losure in 33 patients. The evoked blink reflex in all patients and in 23 controls was also studied. To examine the excitability of facial mo toneurons and bulbar interneurons in individual patients and to compar e the results with EMG findings, R1 and R2 recovery indices were calcu lated in all subjects, as the average of recovery values at 0.5, 0.3, and 0.21 second interstimulus intervals. Based on EMG patterns, the pa tients were divided into three subclasses: EMG subclass 1, 10 patients with involuntary discharges solely in orbicularis oculi muscle; EMG s ubclass 2, 20 patients with involuntary discharges in orbicularis ocul i and either involuntary levator palpebrae inhibition or a disturbed r eciprocal innervation between orbicularis oculi and levator palpebrae; EMG subclass 3, three patients who did not have blepharospasm, but ha d involuntary levator palpebrae inhibition in association with a basal ganglia disease. The total patient group showed an enhanced recovery of both R1 and R2 components compared with controls. Although 30 out o f 33 patients had blepharospasm (EMG subclasses 1 and 2), R1 recovery index was normal in 64% and R2 recovery index was normal in 54%. Patie nts with an abnormal R2 recovery index had an abnormal R1 recovery ind ex significantly more often. All patients from EMG subclass 1 had an a bnormal R2 recovery index, whereas all patients from EMG subclass 3 ha d normal recovery indices for both R1 and R2 responses. Seventy five p er cent of the patients from EMG subclass 2 had normal recovery indice s. The results provide further evidence that physiologically blepharos pasm is not a homogeneous disease entity, and indicate that different pathophysiological mechanisms at the suprasegmental, or segmental leve l, or both are involved.