Insulinomas are rare with an estimated incidence of four cases per million people per year. An insulinoma is the most common cause of hypoglycaemia resulting from endogenous hyperinsulinism.1
It is a curable cause of potentially lethal hypoglycaemia. In 1927, Wilder established the association between hyperinsulinism and a functional islet cell tumour.2
In 1929, Graham achieved the first surgical cure of an islet cell adenoma. Insulinomas can be difficult to diagnose. Symptoms often lead to misdiagnosis as a neurological or psychiatric disorder.3
Insulinomas are characterised clinically by the Whipple triad: episodic hypoglycaemia, central nervous system (CNS) dysfunction temporally related to hypoglycaemia (confusion, anxiety, stupor, paralysis, convulsions, coma), and dramatic reversal of CNS abnormalities by glucose administration. Weight gain occurs in 20–40% of patients.
Imaging studies should only be done after the diagnosis has been confirmed biochemically, because 80% of insulinomas are <2 cm in size and may not be visible by CT scan.
Octreotide scanning localises about half of insulinomas. Pancreatic venous sampling for insulin, via the percutaneous transhepatic route, can successfully localise insulinomas.4
Intraoperative ultrasound can be very useful in identifying occult tumours. About 90% of insulinomas are benign. They may be single or multiple tumours; 80% are solitary adenomas. Insulinomas can occur as part of MEN 1 syndrome, in association with pituitary, parathyroid, and other pancreatic islet tumours (for example, insulinomas, gastrinomas). Less than 10% of insulinomas are associated with MEN-1.
Insulinoma resection achieves cure in 90% of patients and is the therapy of choice.5
Medical treatment with diazoxide or octreotide is indicated in patients with malignant insulinomas and in those who will not or cannot undergo surgery. These measures are designed to prevent hypoglycaemia and, in patients with malignant tumours, to reduce the tumour burden.
- Hypoglycaemia/neuroglycopaenia is sometimes overlooked in patients presenting with signs of impaired brain function.
- An insulinoma is a rare insulin producing tumour and can be difficult to diagnose and localise.
- Symptoms often lead to misdiagnosis as a neurological or psychiatric disorder.
- Insulinoma resection achieves cure in 90% of patients and is the treatment of choice.