Miller Fisher syndrome mimicking ocular myasthenia gravis

PURPOSE.: Miller Fisher syndrome (MFS) is a rare immune-mediated neuropathy that commonly presents with diplopia after the acute onset of complete bilateral external ophthalmoplegia. Ophthalmoplegia is often accompanied by other neurological deficits such as ataxia and areflexia that characterize MFS. Although MFS is a clinical diagnosis, serological confirmation is possible by identifying the anti-GQ1b antibody found in most of the affected patients. We report a patient with MFS who presented with clinical signs suggestive of ocular myasthenia gravis but in whom the correct diagnosis was made on the basis of serological testing for the anti-GQ1b antibody. CASE REPORT.: An 81-year-old white man presented with an acute onset of diplopia after a mild gastrointestinal illness. Clinical examination revealed complete bilateral external ophthalmoplegia and left-sided ptosis. He developed more marked bilateral ptosis, left greater than right, with prolonged attempted upgaze. He was also noted to have a Cogan lid twitch. Same day evaluation by a neuro-ophthalmologist revealed mild left-sided facial and bilateral orbicularis oculi weakness. He had no limb ataxia but exhibited a slightly wide-based gait with difficulty walking heel-to-toe. A provisional diagnosis of ocular myasthenia gravis was made, and anticholinesterase inhibitor therapy was initiated. However, his symptoms did not improve, and serological testing was positive for the anti-GQ1b immunoglobulin G antibody, supporting a diagnosis of MFS. CONCLUSIONS.: Although the predominant ophthalmic feature of MFS is complete bilateral external ophthalmoplegia, it should be recognized that MFS has variable associations with lid and pupillary dysfunction. Such confounding neuro-ophthalmic features require a thorough history, neurological examination, neuroimaging, and serological testing for the anti-GQ1b antibody to arrive at a diagnosis of MFS.