An 84 year old woman presented with intermittent episodes of confusion that had been occurring for over six years. Her sister, with whom she lived, reported that during the episodes, the patient became clammy, confused, and sometimes drowsy. Following one of the early episodes, the patient was investigated for a possible transient ischaemic attack; however, a duplex scan showed only mild carotid disease.

The patient’s symptoms usually occurred at times when she had not eaten for several hours, but occasionally they appeared after a meal. Over the years, her sister had noted that the symptoms could be promptly relieved by giving the patient orange juice. The patient had also learnt to take regular snacks between meals to prevent the symptoms. Consequently, she had gained 9 kg in weight over the six year illness period.

During a particularly severe episode, the patient could not be aroused by her sister and an ambulance was called. The paramedic noted a low capillary blood glucose level of 2.7 mmol/l, and treated her with an intramuscular injection of glucagon. She was fully conscious on arrival at the accident and emergency department. Her serum glucose concentration was 4.1 mmol/l. She had no personal or family history of diabetes mellitus, and was not taking oral hypoglycaemic agents or insulin.