Contralateral reinnervation of midline muscles in facial paralysis

We report on a patient with recovery of activity of the left orbicularis or is and nasalis muscles 3 months after a complete left facial palsy. Stimula tion of the affected facial nerve evoked no responses, whereas contralatera l facial nerve stimulation showed polyphasic responses with very long laten cies in the nasalis and orbicularis oris muscles. Needle electromyography ( EMG) revealed abnormal spontaneous activity in the left orbicularis oris mu scle. The motor unit action potentials on the left side of the face could b e recruited only during marked contraction of the corresponding muscles on the right and were of low voltage and polyphasic ("nascent potentials"). Co ntralateral reinnervation is probably due to sprouting of terminal branches crossing the midline of the face and innervating bundles of muscle fibers on the affected side. This phenomenon seems unfamiliar to most clinicians. Whether the activity is due to conduction along nerve fibers or muscle fibe rs crossing the midline is discussed. (C) 2001 John Wiley & Sons, Inc.