Electrophysiological evidence of cerebellar fiber system involvement in the Miller Fisher syndrome

BackgroundIn the Miller Fisher syndrome (MFS), ataxia may be due involvement of Ia afferents and the cerebellum. Transcranial magnetic stimulation (TMS) over the cerebellum is known to interfere transiently with normal function.MethodsIn this study, we utilized a previously described TMS protocol over the cerebellum in combination with ballistic movements to investigate cerebellar dysfunction in MFS patients.ResultsThe agonist (biceps) reaction time in MFS patients during a motor cancellation task was not significantly reduced during the initial TMS study. However, during the repeat TMS study, significant reduction was seen for all patients, in tandem with clinical recovery. There was significant correlation between anti-GQ1b IgG titers and change in agonist reaction time between the initial and repeat TMS studies.ConclusionsTMS likely affected horizontally orientated parallel fibers in the cerebellar molecular layer. During disease onset, antibody binding may have interfered with facilitation of reaction time during motor cancellation tasks seen in normal subjects. Normalization of reaction time facilitation corresponded to resolution of antibody-mediated interference in the molecular layer.Our study has provided evidence suggesting parallel fiber involvement in MFS, and suggested a role of anti-GQ1b IgG antibody in these changes.