S. EksantivongsN. PoungvarinA. ViriyavejakulJ. PunyameeMahidol University2018-02-272018-02-271994-12-01Journal of the Medical Association of Thailand. Vol.77, No.12 (1994), 627-632012522082-s2.0-0028694454https://repository.li.mahidol.ac.th/handle/20.500.14594/9626Twenty patients with primary hemifacial spasm and ten patients with Parkinson's disease were studied by means of paired stimuli blink reflex. The second stimuli were delivered at a varying time interval between 50-900 ms. The R2 response's absolute refractory periods were compared between patients and twenty one age-matched normal controls as well as between hemifacial spasm and Parkinson's disease. In normal subjects, the mean absolute refractory period was found to be 271.42 +/- 64.36 ms, in hemifacial spasm 160.00 +/- 50.62 ms and in Parkinson's disease 157.14 +/- 53.45 ms. The absolute refractory periods obtained from patients were significantly shorter than in normal controls (p < 0.05). However the values between patients with hemifacial spasm and Parkinson's disease were not (p > 0.05). This result strongly supports bilateral facial motoneurons hyperexcitability as the underlying mechanism of hemifacial spasm.Mahidol UniversityMedicineArticleSCOPUS