A 19-year-old male student attended the neurology clinic with intermittent sensory and motor deficits. These had begun three years earlier when he had woken up with numbness in the medial aspect of the left forearm, little finger, and ulnar half of the ring finger. There was also moderate weakness in the fingers of the left hand, particularly in the extension of the ring and little fingers. The symptoms had persisted for several months, leaving a residual intermittent numbness in the same distribution, particularly for several hours after waking from sleep. Eighteen months before attending the neurology clinic, he had experienced similar symptoms in the right arm, which had persisted for several months before resolving completely.

Three months before attending the clinic, he had woken up with left-sided foot drop, numbness of the dorsum of the left foot (mainly over the tarsal and metatarsal bones), and hyperpathia on the lateral aspect of the left lower leg. The weakness subsequently improved over several months, leaving minimal weakness of ankle dorsiflexion. The sensory deficit in the left lower leg resolved.

There were no other neurological or systemic symptoms. His early development had been normal, although he had not been good at sports. He did not smoke, and did not drink alcohol in excess. There was no family history of either neurological disease or of abnormally shaped feet.

On examination, there was mild wasting of the hypothenar and interossei muscles of both hands, more pronounced on the left. There was mild weakness of left ankle dorsiflexion. Reflexes were absent, apart from both triceps jerks and the left biceps jerk. Plantar responses were flexor. There was hyperpathia over …