GQ1b-Seronegative Miller Fisher Syndrome Associated With Pembrolizumab

A 62-year-old man with a history of metastatic squamous cell carcinoma (SCC) of the scalp, who recently completed 5 cycles of pembrolizumab, presented to the emergency department with 2 weeks of progressive gait ataxia, dysarthria, dysphagia, and diplopia. On physical examination, he had profound areflexia, lower-extremity ataxia, facial diplegia, and ophthalmoplegia. Brain MRI was normal. Lumbar puncture showed albuminocytologic dissociation of 7 white blood cells/µL and protein of 236 mg/dL (normal: 15-45 mg/dL). Additional cerebrospinal fluid (CSF) studies including cytology and flow cytometry were normal. A tentative diagnosis of Miller Fisher syndrome (MFS) was made, and a 5-day course of intravenous immunoglobulin (IVIg) therapy was initiated. Within 2 days, there was marked improvement in facial weakness and ophthalmoplegia. Ganglioside (Asialo-GM1, GM1, GM2, GD1a, GD1b, and GQ1b), acetylcholine receptor (blocking, binding, and modulating), and paraneoplastic (antineuronal nuclear type I/II/III, antiglial nuclear type I, purkinje cell cytoplasmic types I/II/Tr, amphiphysin, CRMP-5, striational, P-/Q-type calcium channel, N-type calcium channel, AChR ganglionic neuronal, and neuronal [V-G] potassium channel) antibodies sent before starting IVIg were within the normal range.