Myokymic discharges and enhanced facial nerve reflex responses after recovery from idiopathic facial palsy.

A functional disorder of facial muscle activity commonly occurs in patients after recovery from Bell's palsy with axonal degeneration. The postparalytic facial dysfunction is probably related to the aberrant growing of regenerating axons, although other theories such as ephaptic transmission, spontaneous generation of impulses, and enhancement of motoneuron excitability should also be considered. In this work, we have carried out a comparative electrophysiological study of both sides of the face in 23 patients who had recovered from a unilateral Bell's palsy with axonal degeneration. At rest, spontaneous firing of motor units was observed in muscles of the previously paralyzed side. Direct motor responses to facial nerve stimulation were smaller in the muscles of the previously paralyzed side, but reflex responses obtained in the same muscles by stimulation of either the facial or trigeminal nerve were larger when compared with those of the contralateral side. These data indicate that patients with "postparalytic facial dysfunction" may have an increased background muscle activity, as well as an enhanced recruitment of facial motoneurons to reflex activation in the side of the previous paralysis. These findings are compatible with an enhanced level of motoneuron excitability in the facial nucleus.