Background IgG anti-GQ1b antibodies are associated with Fisher syndrome (FS), Bickerstaff brainstem encephalitis (BBE), acute ophthalmoparesis and overlap of FS or BBE with Guillain–Barré syndrome (GBS) (FS/GBS or BBE/GBS). It has not been clearly established if the primary pathology of these disorders is demyelinating or axonal in nature. Rapid resolution of conduction slowing or block without signs of demyelination–remyelination has been reported in axonal subtypes of GBS that are associated with IgG anti-GM1 or -GD1a antibodies. We hypothesised that such reversible conduction failure would be also observed in FS and related disorders.

Methods Serial nerve conduction studies were prospectively performed in 15 patients with FS and related conditions.

Results Neither conduction block nor abnormal temporal dispersion was observed in any of the nerves at any point in all the patients. Conduction velocities for none of the nerves were in the demyelinating range. The amplitude of sensory nerve action potential was decreased in three FS, one FS/GBS and two BBE/GBS patients. Compound muscle action potential amplitudes were decreased in the two BBE/GBS patients. These decreases in amplitudes of sensory nerve action potential and compound muscle action potential promptly resolved without significant change in duration on serial studies.

Conclusions Reversible conduction failure was seen in six of the 15 patients with FS and related disorders on serial nerve conduction studies. There were no signs of demyelination or remyelination in the 15 patients. The pathology appears to be primarily non-demyelinating. We believe these conditions form a continuous spectrum with axonal GBS.