Background Ataxic Guillain–Barré syndrome is characterised by profound ataxia with negative Romberg sign and no ophthalmoplegia. Its nosological relationship to acute sensory ataxic neuropathy has yet to be discussed.

Methods Medical records were reviewed of patients suffering acute ataxia and reduced muscle stretch reflexes but without external ophthalmoplegia. Clinical features and laboratory findings were analysed. Rat muscle spindles were immunostained by anti-GQ1b and -GD1b antibodies.

Results The Romberg sign was negative in 37 (69%) of 54 patients with acute ataxic neuropathy without ophthalmoplegia, but positive in the other 17 (31%). The negative and positive subgroups had similar features; preceding infectious symptoms (86% vs 83%), distal paraesthesias (70% vs 88%), superficial sense impairment (27% vs 24%), IgG antibodies to GQ1b (65% vs 18%) and GD1b (46% vs 47%) and cerebrospinal fluid albuminocytological dissociation (30% vs 39%). Findings did not differ between the subgroups of 466 patients with Fisher syndrome with and without sensory ataxia. Acute ataxic neuropathy patients more often had anti-GD1b (46% vs 26%) and less often anti-GQ1b (50% vs 83%) antibodies than Fisher syndrome. Anti-GQ1b and -GD1b antibodies strongly stained parvalbumin-positive nerves in rat muscle spindles, indicative that proprioceptive nerves highly express GQ1b and GD1b.

Conclusion Clinical and laboratory features suggest that ataxic Guillain–Barré syndrome and acute sensory ataxic neuropathy form a continuous spectrum. The two conditions could be comprehensively referred to as ‘acute ataxic neuropathy (without ophthalmoplegia)’ to avoid nosological confusion because Fisher syndrome is not classified by the absence or presence of sensory ataxia. That is, acute ataxic neuropathy can be positioned as an incomplete form of Fisher syndrome.