The patient was a 50-year-old West African man who had lived in the UK for 11 years but who travelled widely in Europe in the context of his job. He was hepatitis B positive. He presented with a 6-week history of gradually increasing pain in both thighs exacerbated by walking, and a 3-week history of gradually increasing weakness of both hips, worse on the right. There was no prodromal febrile illness. His mobility was markedly reduced and he was restricted to crawling around his house and using a borrowed wheelchair. He had a history of low back pain, but with no recent worsening of this pain. His arms, bladder, bowels, buttocks and leg sensation were normal. He took no regular medications apart from painkillers.

On examination, his cranial nerve function and his arms were normal. There was wasting of both quadriceps with weakness of hip flexion and extension (strength 2/5), knee flexion and extension (strength 4/5) but normal ankle dorsiflexion and extension. Sensation and coordination were intact. The reflexes were absent except for the right knee jerk which was present on reinforcement. The plantar reflexes were flexor.

A lumbar puncture was performed. The cerebrospinal fluid (CSF) was straw-coloured because of a markedly elevated protein of 6.12 g/l (0.18–0.40), with 2 leukocytes (subtype unstated) and fewer than 1 erythrocyte per µl. The CSF/serum to glucose ratio was 1:3. Serum creatine kinase level was normal, and a HIV test was negative.

He had attended a different hospital 5 years previously, describing very similar symptoms. However, at that time, he had also experienced left arm weakness (strength 1/5 …