Pathophysiologic Approach by Blink Reflex and EMG Studies in Essential Blepharospasm Comparison with Other Facial Involuntary Movement

ABSTRACT

Background and objectives: Blepharospasm (BS) is best categorized as focal dystonia, but the biochemical and neuroanatomical mechanisms are poorly understood. We performed this study in order to postulate the pathophysiologic mechanism of essential BS, using blink reflex test and EMG studies. METHODS: We studied 24 patients with essential BS and 51 normal adults. Blink reflex tests and EMG on orbicularis oculi muscle were performed in all patients. We evaluated our electrophysiological data, comparing with those obtained from other studies, in which bulbocavernosus reflex, H-reflex, and T-reflex tests were done. We also compared our EMG data with those of hemifacial spasm and facial myokymia in other studies. Results: 1. Rl response latency of blink reflex test in 24 patients with essential BS was not changed, but R2 latency in the papient group was significantly shortened, comparing with those of normal control group. These results can be explained by overexcitability of the interneuron with polysynaptic pathway. Another supporting evidence is the fact that the latency of polysynaptic bulbocavernous reflex test in upper motor neuron lesion is shorter than normal control, although the latency of monosynaptic H-reflex and T-reflex test are not changed. 2. EMG on orbicularis oculi muscle in patients with essential BS showed spontaneous MUPs at irregular intervals at rest, while those in patients with hemifacial spasm and facial myokymia, known to be caused by overexcitability of facial nucleus, showed spontaneous MUPs at regular intervals. EMG in patients with essential BS, during the period of spasm, showed relatively long brief bursts at irregular intervals from 30 to 100 ms, lasting inconstant duration ranging from 30 to 300 ms. CONCULSIONS It is suggested that the pathophysiology of essential BS is overexcitability of interneuron due to disinhibition in inhibitory interneuron, and that EMG findings of essential BS are remarkably different from those of hemifacial spasm and facial myokymia.