Insulinoma is a rare tumour, but is the commonest cause of hyperinsulinaemic hypoglycaemia in adults. It is characterised by symptomatic hypoglycaemia with inappropriately elevated plasma insulin and C-peptide levels. 10% of insulinomas are malignant. The coexistence of insulinoma with diabetes mellitus is extremely rare with only 20 previously reported cases. This can therefore pose a diagnostic challenge.
An 83 year old man, who developed Type 2 diabetes in 1999, was treated satisfactorily with dietary therapy alone. In October 2006 he was admitted to hospital after being found collapsed at home following a three-day diarrhoeal illness. On admission his random blood glucose was 1.90 mmol/l but despite appropriate treatment he continued to experience recurrent hypoglycaemia. Endogenous hyperinsulinism was confirmed by demonstrating elevated insulin and C-peptide levels during hypoglycaemic episodes. Abdominal computerised tomography scan revealed a hypervascular mass in the tail of the pancreas with multiple hepatic metastases. Ultrasound guided liver biopsy confirmed the diagnosis of a malignant neuro-endocrine tumour. To prevent further hypoglycaemia he was treated with diazoxide and his management was transferred to oncology. The possibility of a co-existing insulinoma should be considered when unexplained hypoglycaemia occurs in a patient with previously stable diabetes.