Continuous glucose monitoring in patients with insulinoma

Abstract

Insulinomas are rare neuroendocrine tumours that are usually small and may take time to localize. They cause recurrent life-threatening spontaneous hypoglycaemia. Recurrent hypoglycaemia causes loss of hypoglycaemia awareness, putting the patient at further risk, but this has rarely been described in insulinoma. We describe the utility of continuous glucose monitoring (CGM) in patients with insulinoma. Three patients, aged 72 years (patient 1), 37 years (patient 2) and 24 years (patient 3), with suspected insulinoma attended our investigation unit, in a university teaching hospital. Biochemical diagnosis was confirmed by elevated plasma insulin and C-peptide during biochemical hypoglycaemia [plasma glucose < 2.2 mM (40 mg/dl)]. Surgery confirmed histology in all. CGM was used to monitor frequency and time of hypoglycaemia during diagnosis and medical treatment, and after definitive surgical treatment. All patients had evidence of hypoglycaemia unawareness. At diagnosis in patients 1-3, CGM revealed 6.1%, 21.9% and 71.0% of time spent in moderate hypoglycaemia (plasma glucose 2.2-3.0 mM), and 1.4%, 11.4% and 48.1% of time in severe hypoglycaemia (plasma glucose < 2.2 mM), respectively. On diazoxide this reduced to 0.6%, 5.4% and 5.7% time in moderate hypoglycaemia, and no severe hypoglycaemia in patients 1 and 3, and 0.5% in patient 2. Octreotide therapy in patients 2 and 3 resulted in 5.8% and 0% of time in moderate hypoglycaemia, respectively, and no severe hypoglycaemia. After surgical excision CGM confirmed cure in all. CGM in insulinoma is useful in detecting hypoglycaemia, and hypoglycaemia unawareness, monitoring response to medical therapy and for confirming cure postoperatively, and is useful in the management of this uncommon but dangerous condition.