Case history

A 51-year-old man presented to the neurology clinic with numbness affecting the left side of his chin, which had developed over a few days. Three weeks later, he reported pain affecting the left side of his face, locking of the jaw on chewing and numbness of the left side of the tongue.

He worked as a maintenance fitter in a sewage works and had suffered exposure to raw sewage 2 months before his clinic visit, followed by diarrhoea and vomiting. Serological testing for leptospirosis was negative. These symptoms had settled before the numbness developed.

He had no headaches or visual symptoms. His swallowing and speech were normal. He had lost 10 kg in weight over the previous 3 months. He had a strong family history of bowel carcinoma but a recent screening colonoscopy with biopsies was negative. He had never smoked and only drank alcohol occasionally.

On examination, he had reduced sensation to light touch and pain over the left side of his chin and lower lip. The sensation over the rest of his face was normal; his corneal reflexes were present bilaterally and his jaw power was normal. Examination of the other cranial nerves and limbs was normal. His general physical examination was unremarkable.

His full blood count, erythrocyte sedimentation rate, plasma glucose, urea and electrolytes, serum C reactive protein, calcium and liver function tests were normal apart from a raised …