A 68-year-old man developed “pins and needles” of his fingertips and toes in December 2005 along with cramp-like muscle pains in his forearms and calves. Over the next 6 months he noticed “coldness” of his hands and feet, his arms felt “sore” and his fingers were often “shaky” and felt “gritty”. His feet felt as though they were “covered in sand” and he became unsteady. By June 2006 he was frequently falling. He described “not knowing where” his feet were and his “knees giving way”. By November 2006 his mobility was restricted to using a wheelchair. He also had difficulty with manual dexterity, leading to problems with dressing and feeding. Over this period he had intermittent diarrhoea and constipation but his weight and appetite were stable. His past medical history is outlined in table 1 and included longstanding abdominal pain and alteration in bowel habit for which he had been extensively investigated.

In November 2006 his medications included: fluoxetine 20 mg once daily for depression, omeprazole 20 mg once daily, folic acid 5 mg once daily, Adcal D3 three tablets once daily, ferrous sulphate 200 mg three times a day, alfacalcidol 1 μg once daily, hyoscine butlylbromide 10 mg three times a day, and intramuscular vitamin B12 injections 1 mg every 3 month which he had been receiving for the past 10 years. There was no family history of neurological illness. He was an ex-smoker who had given up 36 years previously, and he consumed alcohol occasionally.

On examination in November 2006 he was thin, weighing only 50.2 kg (body mass index 17.5 kg/m²). There was finger clubbing but no generalised lymphadenopathy and the rest of the general examination was unremarkable. He had normal higher mental function, cranial nerves and speech, muscle bulk and tone, and full power in …