Lesson of the week: Are spontaneous hypoglycaemia, raised plasma insulin and c peptide concentrations, and abnormal pancreatic images enough to diagnose insulinoma?

Spontaneous fasting hypoglycaemia is rare, and in adults the usual underlying cause is insulinoma.1 Most insulinomas are small tumours, and currently available imaging techniques fail to detect a large proportion of them, so that the diagnosis may have to be based on the presence of spontaneous hypoglycaemia associated with inappropriately raised plasma insulin and C peptide concentrations. In such cases laparotomy with exploration of the pancreas may be the next logical step. A 42 year old nurse presented with a five month history of dizziness, ataxia, and paraesthesiae, which improved after eating carbohydrates. Her medical history included acute sarcoidosis, which had resolved 24 years ago, temporal lobe epilepsy diagnosed 13 years previously, and episodic numbness of her right shoulder and face for 12 years, the cause of which had been attributed to possible demyelination. She took sodium valproate to control her epilepsy. She did not smoke and drank minimal quantities of alcohol. Clinical examination did not indicate any abnormality. During a supervised 24 hour fast in hospital she remained symptom free with normal glucose concentrations. Four months later her symptoms became more frequent and severe. On several occasions her plasma glucose concentration was in the hypoglycaemic range (1.7-2.2 mmol/l) and accompanied by symptoms: these resolved with the administration of …