A 63-year-old man presented with a three-month history of non-specific generalised headache. For about two weeks, he had also become more forgetful, and had developed episodes of odd behaviour lasting several hours or days, during which he would wander and get lost, or his speech would appear out of context. During one such episode he failed to recognise his daughter as the mother of his new grandson. This prompted his family to seek medical attention. The patient had otherwise been in good health, with no medical problems in the past. He was a non-smoker, reported drinking two bottles of wine per week, and he used to work as a secondary school teacher, but had retired to a remote Scottish island four years previously where he worked as a horticulturalist.

On admission to the local hospital general physical, neurological and mini-mental state examination were all normal, as were routine blood tests including inflammatory markers. A CT brain scan showed slight contrast enhancement in the right medial temporal lobe (fig 1). A subsequent MR brain scan (T2-FLAIR) showed high signal in the right hippocampus (fig 2). The cerebrospinal fluid (CSF) was abnormal, with 76 white blood cells/mm³ (normal lymphocytes), protein 1.79 g/l, and glucose 3.3 mmol/l (serum glucose 5.7 mmol/l). At this stage, the patient was transferred to the regional neurology unit, where, within hours of admission, he had a generalised seizure. Following admission he continued to be muddled and to have a tendency to wander off the ward. Neurological examination showed no deficit. However, on the Addenbrooke’s Cognitive Examination, the patient showed marked memory problems, and neuropsychological assessment confirmed deficits in memory and attention.