Insulinoma

An insulinoma is a rare tumour of the insulin-producing cells of the pancreas. Almost all are small and benign, but they secrete insulin without regard to the body's needs. Because insulin lowers blood sugar, an insulinoma causes repeated episodes of hypoglycaemia (low blood glucose), classically when the person has not eaten for a while — overnight, before meals, or after exertion. The symptoms come in two groups: those from the low sugar affecting the brain (confusion, difficulty concentrating, odd behaviour, drowsiness and, if severe, seizures or loss of consciousness), and those from the body's adrenaline response (shakiness, sweating, palpitations, hunger and anxiety). A telling feature is that the symptoms are promptly relieved by eating or by sugar. The key to diagnosis is capturing the biochemistry during a genuine low — often with a closely supervised fast — and showing an inappropriately high insulin and C-peptide at a time when the glucose is low and insulin should have switched off. C-peptide is measured because it distinguishes the body's own insulin (raised in insulinoma) from injected insulin. Imaging then locates the tumour, which can usually be removed surgically, curing the condition.

• Insulin — inappropriately high during a low blood sugar (should be suppressed when glucose is low).
• C-peptide — also high, confirming the insulin is the body's own (not injected).
• Fasting glucose — low during episodes; a supervised fast is often used to provoke and capture a low.
• Blood glucose during symptoms — documents the hypoglycaemia; symptoms relieve with sugar.

• Shakiness, sweating and palpitations
• Intense hunger, especially before meals or when fasting
• Dizziness or light-headedness when hungry
• Confusion, difficulty concentrating or odd behaviour
• Drowsiness and, if severe, seizures or loss of consciousness
• Symptoms relieved promptly by eating or sugar
• Sometimes weight gain from eating to prevent lows