Endocrine Abstracts

Insulinoma is a rare but potentially treatable cause of hypoglycaemia. We present a case where achieving a diagnosis of insulinoma was complicated by evidence of low serum insulin levels during documented biochemical hypoglycaemia.

A 58 year old lady presented with weight gain and daily episodes of shaking, hot flushes and disorientation that were relieved by the ingestion of food. During symptomatic episodes home capillary blood glucose measurements suggested hypoglycaemia.

Baseline biochemistry and a urinary sulphonylurea screen were negative.

A 72 h fast was undertaken. Eight hours into the fast the patient became confused, aggressive and shaky. A laboratory serum glucose taken during the episode was low (2.1 mmol/l (NR=3.5–6.0)). Serum insulin and C-peptide levels were also low. (Insulin=3.3 mIU/l (NR=2.6–24.9) and C-peptide =0.7 mcg/l (NR=1.15–4.5).

A spiral contrast CT showed a 1 cm hypodense nodule in the proximal body of the pancreas. A subsequent test carried out on the serum obtained during hypoglycaemia revealed an elevated pro-insulin level (32.7 pmol/l (NR 6.4–9.4))

A medial pancreatectomy was performed and the histology on the tumour resected showed a well-differentiated pancreatic endocrine neoplasm consistent with a diagnosis of insulinoma. The patient made an excellent recovery and is now asymptomatic.

Pro-insulin is often the dominant hormone produced by insulinomas but pro-insulin levels are not always measured during hypoglycaemia. Older insulin assays demonstrate cross-reactivity, inadvertently measuring a combination of insulin and pro-insulin. However, newer insulin assays are more specific. This case therefore highlights the importance of routinely measuring pro-insulin levels in all patients during hypoglycaemia. There is a risk of missing a diagnosis of insulinoma if pro-insulin is not measured.