O153 Prepulse inhibition is deficient in hemifacial spasm

Abstract

Objective Hemifacial spasm (HFS) is characterized by spasms of facial muscles on one side of face. There are two hypothesis in the pathogenesis: a peripheral nerve hypothesis or hyperexcitability of the facial nucleus. Blink reflex (BR) excitability is increased in HFS. Here, we aimed to analyze the changes of BR-prepulse inhibition (PPI) which provides assessment of inhibitory control on facial circuitry. Patients and method We included 13 patients with HFS and 13 healthy subjects. Baseline BR, BR recovery at ISI of 300 ms and BR-PPI at ISI of 100 ms were performed on the right sides of healthy subjects and on the asymptomatic and symptomatic sides of patients. Latency, amplitude and area of R1 and R2 were measured in all tests and compared among two groups using Mann-Whitney U test and t-test for paired groups when appropriate. Results Baseline values of R1 and R2 were normal and similar among groups. The mean recovery of R2 area was the higher on both symptomatic side of HFS (77.5%) compared to asymptomatic side of HFS (46.5%) and compared to healthy subjects (27.2%, p = 0.007). All groups had inhibition during BR-PPI. However, PPI was low on both sides of HFS compared to healthy subjects (p = 0.010). There was no correlation between disease duration and recovery of BR or BR-PPI. Conclusions HFS patients in this study had increased recovery of BR indicating increased excitability of BR circuit which was bilateral but more prominent on the symptomatic side. Similarly, inhibitory control upon BR circuit was prominently reduced on bilateral sides in HFS group. Significance This study discloses the central changes in HFS.