The H reflex as a diagnostic tool for Miller Fisher syndrome in pediatric patients.

Miller Fisher syndrome (MFS) is characterized by gait ataxia, external ophthalmoplegia and areflexia. Immunohistochemical studies suggest a pathophysiological role for anti-GQ1b antibodies at the paranodal regions of the oculomotor nerves, at some neurons of the dorsal root ganglia (DRG) and at motor nerve terminals. The variability of abnormal electrophysiological findings reported is significant. Nerve conduction studies, H reflex and F waves were performed in three pediatric patients with MFS. The H reflex was absent in all three patients. It was the sole abnormality in two patients whereas the third patient also had extended motor and sensory nerve conduction impairments. The transient character of this isolated absence has been confirmed in one patient. These data point to a proximal demyelinating process near the DRG. This may involve selective demyelination of Ia spinocerebellar afferent fibers originating in muscle spindles. In a pediatric practice, the H reflex seems to be a useful tool in the diagnostic approach to MFS.