CLINICAL AND ELECTROMYOGRAPHIC FEATURES OF LEVATOR PALPEBRAE-SUPERIORIS MUSCLE DYSFUNCTION IN INVOLUNTARY EYELID CLOSURE

We report on five patients with involuntary eyelid closure, diagnosed as blepharospasm and referred to us for treatment with botulinum A tox in. Synchronous electromyographic (EMG) recording was performed from t he levator palpebrae superioris (LP) and the orbicularis oculi (OO) mu scles. In the first two cases, EMG registration showed alternating, se mirhythmic dystonic activities in both the LP and OO, clinically perce ptible as ''flickering'' of the eyelids. While the eyelids were lowere d, one of them also showed involuntary upper eyelid tractions due to d ystonic activities of LP. In the third patient, EMG patterns were char acterized by a gradual decrease in the level of LP activity, followed by the contraction of OO, which facilitated the return of LP to its to nic activity, termed ''postinhibition potentiation'' of LP. In the fou rth patient, EMG recording showed involuntary inhibition of LP in comb ination with blepharospasm. Involuntary closure of the eyelids in the fifth patient was caused by short or prolonged periods of involuntary LP inhibition, whereas OO activity remained normal. Our results provid e further evidence that LP muscle activities are regulated by burst-to nic motoneurons, and we suggest that these motoneurons, and/or the inp ut signals regulating their activities, can be involved independently in a pathological process. Clinical symptoms are discussed that may be helpful to recognize those cases with LP motor dysfunction, whether o r not accompanied by OO activity disorders. Because the term blepharos pasm indicates an abnormal motor function of OO, we propose ''blepharo spasm-plus'' to designate those cases with a combined motor dysfunctio n of LP and OO muscles.