Miller-Fisher Syndrome: Is the ataxia central or peripheral?

A 50-year-old man presented with a brief history of slurred speech, unsteadiness, double vision and paraesthesia. He had been unwell for 12 days with campylobacter gastroenteritis. On examination, there was ophthalmoplegia, nystagmus, areflexia and lower limb and gait ataxia. Serological testing was positive for GQ1b antibody in keeping with the diagnosis of Miller Fisher Syndrome (MFS). He was treated with two courses of intravenous immunoglobulins and made a good recovery, only displaying mild gait ataxia when reviewed in clinic 2.5 months later. There has long been a debate as to whether the ataxia in MFS originates in the cerebellum or it is more peripheral. In this case, magnetic resonance spectroscopy (MRS) revealed a reduced NAA/Cr ratio in the cerebellar vermis and right cerebral hemisphere, suggestive of cerebellar dysfunction. The NAA/Cr normalised 2.5 months later reflecting the clinical recovery. The findings on MRS suggest that the cerebellum is involved in MFS.