Abstract

A 42-year-old woman who experienced more than 50 attacks of left-sided facial palsies after exposure to chlorocresol was studied. Only muscles around the left side of the mouth were affected. On neurophysiological testing during chlorocresol provocation the only abnormality was a loss of motor units during maximal contraction of the left orbicularis oris muscle. This could be explained by a peripheral as well as a central effect. Extensive electrophysiological examination without chlorocresol provocation excluded a preexisting generalised nerve disorder and other diagnostic procedures did not give evidence of pathology involving the left facial nerve. A hyperreactive mechanism causing a transient block of the left facial nerve is proposed.