A 32-year-old woman presented at 27 weeks gestation with new-onset diplopia. She awoke with persistent binocular horizontal diplopia. She denied headache, ocular pain, or other associated neurologic symptoms. There were no previous episodes. A month prior to review, 4 of her family members had diarrheal illness; the patient experienced minor nausea for 1 day only and attributed this to morning sickness. She has no relevant medical history and is usually fit and well. Her pregnancy had been uncomplicated; she was reviewed by her midwife, who reported no fever, hypertension, hyperglycemia, or proteinuria. Initial examination demonstrated a right esotropia and bilateral restriction in abduction, right greater than left, indicating bilateral sixth nerve palsy. Further ophthalmic examination was normal, demonstrating an intact visual field with no evidence of afferent pupillary defect, nystagmus, or papilledema. The rest of the cranial nerve examination was unremarkable. There were no bulbar signs, eyelid ptosis, or muscle fatigability. Peripheral neurologic examination demonstrated absent reflexes in both upper limbs and blunted reflexes in both lower limbs. There were no motor deficits or gait ataxia.