Reorganization of sensory input at brainstem in hemifacial spasm and postparalytic facial syndrome

We hypothesized the filtering of sensory input from face and hand at brainstem may reorganize in hemifacial spasm (HFS) and postparalytic facial syndrome (PFS). Thus, we examined the prepulse inhibition of blink reflex (BR-PPI) in HFS and PFS. We included 12 healthy subjects, 13 patients with HFS, and 11 patients with PFS. Baseline BR, BR recovery at interstimulus interval (ISI) of 300 ms and BR-PPI at ISI of 100 ms were performed on the right sides of healthy subjects and on both sides of patients. Within-subject analysis showed baseline BR and BR-PPI were similar between asymptomatic and symptomatic sides of patients with HFS whereas BR recovery was higher on the symptomatic side. In the PFS group, latency of R2 during baseline BR recording was longer ( p = 0.022) and R2 amplitude ( p = 0.046) was reduced on the symptomatic side compared to asymptomatic side. Reduction of R2 area in BR-PPI recordings was also the lowest in HFS compared to other two groups ( p = 0.000); however, it was also lower in patients with PFS compared to healthy subjects ( p = 0.018). BR-PPI was decreased on both sides of patients. The mean R2 recovery was higher on both sides of patients with HFS and PFS ( p = 0.007). Filtering of facial sensory input is decreased probably to monitor and to correct the sequence of facial movements in these disorders.