MRCP2-3045

MRCP2-3045

A 50-year-old man presents with diplopia, dysarthria, and difficulty swallowing. Over the next few days, he develops weakness in his upper and lower limbs, and by day four, he is unable to walk unaided. He denies any sensory symptoms or bladder disturbances and has no significant medical history. He is a non-smoker, does not drink alcohol excessively, and does not take any drugs. On examination, he has bilateral dilated and fixed pupils, binocular diplopia, and weak cough. His vital capacity is reduced, and he has lower motor neurone tetraparesis. He is hyporeflexic with normal sensation. Investigations, including blood tests, CT scan, nerve conduction studies, and EMG, are normal. What is the most likely diagnosis?