Auditory evoked blink reflex and posterior auricular muscle response: Observations in patients with HFS and PFS

Our goal was to investigate the characteristics of the auditory brainstem reflexes in patients with hemifacial spasm (HFS) and postparalytic facial syndrome (PFS).

The spasm activities and responses by supraorbital and auditory stimuli were recorded from the orbicularis oculi, the posterior auricular and the mentalis muscles in 27 HFS and 21 PFS patients. The results were compared with those of 20 controls.

Blink reflex (BR) was obtained by supraorbital stimulation in normal controls and on both sides of HFS and PFS patients whereas sound evoked bilateral auditory blink reflex (ABR) in 96.3%, 90.5% and 100%, respectively. Both BR and ABR showed synkinetic spread on symptomatic sides in all patients. The posterior auricular muscle response (PAMR) was observed bilaterally in 59.3%, 42.9% and 75.0% of groups, respectively. However, there was no synkinetic spread of PAMR.

Since PAMR does not show synkinetic spread even in the presence of synkinetic spread of ABR and BR, we may suggest that a distal origin may be responsible of the synkinetic spread, or PAM is probably governed by a smaller nucleus in the brainstem. Thus it may be speculated that its excitability is insufficient to stimulate the ABR nucleus, whereas the reverse process is possible.