Blink reflexes and lateral spreading in patients with synkinesia after Bell's palsy and in hemifacial spasm

We compared various electrodiagnostical tests in patients with hemifacial s pasm and in patients who developed synkinesia after Bell's palsy. We examin ed the evoked blink reflexes in the orbicularis oculi (o. oculi) and orbicu laris oris (o. oris) muscles in 23 patients with hemifacial spasm (HFS), in 10 patients with synkinesia after Bell's palsy (BPS) and in 22 control sub jects. In the patient groups, we recorded synkinesia, latency and amplitude of compound muscle action potential (CMAP) in the mental muscle after stim ulation of the facial nerve and we examined electromyographic activity of t he o. oculi and mental muscles synchronously. Furthermore, we studied the p henomenon of lateral spreading, also known as ephaptic transmission, betwee n the different facial nerve branches. Patients with BPS had a prolonged R1 latency on the affected side in o. oculi and smaller mental CMAP amplitude as an indication of facial nerve damage and nerve fiber loss. This was not found in patients with HFS, who showed an increased amplitude showed only an increased R1 amplitude in o. oris. All patients had signs of synkinesia. Lateral spreading with different patterns was present in all patients with HFS and in half of the patients with BPS. Latencies of early and late resp onses showed no differences between HFS and BPS. In addition to alterations in facial nucleus excitability in both conditions, ectopic re-excitation o f facial nerve axons in HFS may explain the differences in neurophysiologic al findings between HFS and BPS patients. A loss of control following synap tic stripping may also be a contributing factor. Copyright (C) 2000 S. Karg er AG, Basel.