Serial single fiber electromyography (SFEMG) examinations of orbicularis oc
uli muscle in patients with blepharospasm or hemifacial spasm treated with
botulinum toxin injections were performed. The aim of the study was to eval
uate the impairment of neuromuscular transmission, to follow reinervation a
fter botulinum toxin administration and to find out whether there was a rel
ationship between SFEMG parameters and clinical symptoms. Examinations were
performed before injection, during early and late remission of symptoms, a
nd after recurrence of the involuntary movement. Severe impairment of neuro
muscular transmission, as revealed by increased jitter and increased presen
ce of abnormal potential pairs and pairs with blocking, was found in early
remission, but fiber density remained unchanged when compared with pretreat
ment values. In late remission, increased fiber density was registered for
the first time. The recurrence of involuntary movements was related to the
further increase of fiber density and tendency to normalization of jitter p
arameters. The study therefore suggests that formation of new neuromuscular
junctions and their functional maturation is responsible for muscle recove
ry after botulinum toxin administration, Eur J Neurol 6:461-467 (C) 1999 Li
ppincott Williams & Wilkins.