Demyelinating features in sensory nerve conduction in Fisher syndrome

A significant number of patients with Fisher syndrome (FS) exhibit sensory symptoms in addition to the classical triad of opthalmoplegia, ataxia and areflexia. Previous studies have shown the amplitudes of sensory nerve action potentials (SNAPs) to decrease in patients with FS, thus implying the presence of an axonal pathology in the sensory nerves.

We included ten consecutive patients with FS who were divided into the following two groups: those with hypesthesia (group H) and those without hypesthesia (group NS). The parameters obtained from nerve conduction studies (amplitudes of compound muscle action potentials, motor conduction velocities, amplitudes/duration of SNAPs and sensory conduction velocities) were retrospectively compared between the two groups. In addition, follow-up sensory nerve conduction studies were conducted in one representative patient from each group.

Of the 10 patients with FS, four (40%) showed hypesthesia and eight (80%) showed distal paresthesia. The amplitudes of the SNAPs of both the median and sural nerves were lower in group H than in group NS. Moreover, the duration of the sural SNAPs was longer in group H than in group NS. Desynchronization of SNAPs in the acute phase was observed during follow-up in both patients who underwent follow-up studies.

The prolonged duration of SNAPs in group H and the desynchronization of SNAPs in the two patients who underwent follow-up studies suggest the presence of a concomitant demyelinating process in the sensory nerves.