Excitability of facial nucleus and related brain-stem reflexes in hemifacial spasm, post-facial palsy synkinesis and facial myokymia

Objective To compare the electrophysiological excitability characteristics of the facial nucleus and related structures in hemifacial spasm (HFS), post-facial palsy synkinesis (PFPS) and facial myokymia (FM). Methods Facial F-waves, blink reflex recoveries and magnetically elicited silent periods (SP) were prospectively studied in 17 HFS, 17 PFPS, 8 FM cases and in 13 controls. Earlier unpublished observations on abnormal impulse transmission in 36 HFS and 29 PFPS cases were also included. Results Enhanced F-waves were recorded on the symptomatic side in PFPS and HFS cases with a tendency to be more pronounced in PFPS. HFS and PFPS groups both showed an earlier blink reflex recovery, more prominent in PFPS patients, when stimulated and/or recorded on the symptomatic side. Unelicitable SPs were encountered after 24/39 stimulations in 5 patients with PFPS and rarely in HFS cases. Duration of elicitable SPs did not change remarkably. FM group had similar characteristics as normal controls in the 3 electrophysiological tests. Latencies of the lateral and synkinetic spread responses were significantly prolonged in the earlier PFPS group as compared to HFS. In two-point stimulation, both groups showed a greater latency shift in late responses, again more pronounced in PFPS. Conclusions PFPS and HFS cases had similar enhanced excitability patterns at the facial nucleus and related brain-stem structures, more marked on the symptomatic side and more obvious in the PFPS group. Findings elicited in the FM group were thought to be caused by asynchronous hyperactivity of facial motoneurons. Significance In this comparative electrophysiological study, similar excitability patterns were found in HFS and PFPS groups, albeit with different intensities.