Background: Insulinomas are rare neuroendocrine tumours with an incidence of four cases per million a year. Only few cases of insulinoma in patients with preexisting diabetes mellitus have been reported.
Case: We present a 50-year-old male with type 2 diabetes mellitus who suffered from recurring hypoglycemia. He had gained 20 kilograms of weight in five years. 72-hour fast revealed hypoglycaemia in the presence of inadequately high C-peptide and insulin levels. Magnetic resonance imaging and selective arterial calcium stimulation test confirmed a mass in the body of the pancreas. The tumor was removed surgically. Pathological examination demonstrated a benign insulinoma. Postoperatively, blood glucose levels were within the therapeutic range. The HbA (1c) value was 6.8 % three months after the intervention.
Conclusion: Clinicians should be alert to insulinoma as a, though rare, differential diagnosis of hypoglycaemia in diabetes, in particular in patients with recurrent, otherwise unexplained hypoglycaemia.