24th July 2023

Insulinomas

Insulinomas are a rare form of pancreatic tumour, deriving from the beta cells of the islets of Langerhans in the pancreas. They are a type of neuroendocrine tumour and are generally benign, although a very small percentage may metastasise.

They are important to be aware of as a cause of hypoglycaemia, especially if severe, refractory, and unrelated to concomitant diabetes mellitus. Common symptoms are those of hypoglycaemia, i.e. sweating, tremor, presyncope and palpitations. More seriously, they can also cause neurological symptoms, such as confusion, behaviour and personality changes, visual disturbances, seizure, and coma.

Diagnosis should be suspected in any patient with symptomatic ‘true’ hypoglycaemia, which is defined by Whipple’s triad as:

• Signs and symptoms of hypoglycaemia
• Blood glucose level of less than or equal to 2.5 mmol/L
• Reversibility of symptoms with glucose administration

A full hypogylcaemia panel should then be done, including glucose, insulin and C-peptide levels. C-peptide is associated with endogenous insulin and hence will be elevated in cases of insulinoma. The prolonged fasting test is often diagnostic. Normally, endogenous insulin is suppressed in hypoglycaemia; if a patient has an insulinoma, then a 72-hour fast will fail to suppress insulin levels. CT and MRI can then be done to localise the site of the tumour.

The first line treatment for resectable tumours is surgery – which often includes removal of part of the pancreas – and the majority of insulinomas may be cured this way. Non-resectable tumours can be managed with the somatostatin analogue octreotide, which works by inhibiting insulin secretion.