Endocrine Abstracts

Background: Hypoglycaemia in adults without diabetes requires systematic evaluation to determine its aetiology. Although insulinoma is the most frequent cause of endogenous hyperinsulinaemic hypoglycaemia, proinsulin-secreting tumours are rare and diagnostically challenging.

Case Description: A 65-year-old man presented with recurrent episodes of sweating, confusion, and dizziness that improved promptly with oral glucose intake. On hospital admission, symptomatic hypoglycaemia was confirmed with a plasma glucose of [insert actual value], thus fulfilling Whipple’s triad. The patient had no history of diabetes, did not take insulin or oral hypoglycaemic agents, and denied alcohol excess. His past medical history included multiple comorbidity, with no relevant family history.

Clinical Hypothesis: Proinsulinomas are characterised by disproportionate secretion of proinsulin, with suppressed or inappropriately normal insulin and C-peptide levels during hypoglycaemic episodes.

Diagnostic Pathway: During symptomatic hypoglycaemia, his plasma glucose was 2.0-3.0, insulin and C Peptide as inappropriately low/normal but proinsulin was markedly elevated. These findings indicated endogenous hyperinsulinaemic hypoglycaemia driven predominantly by proinsulin secretion.

Discussion and Learning Points: This case highlights the importance of recognising the biochemical pattern of disproportionately elevated proinsulin in the absence of raised insulin and C-peptide. Proinsulin-secreting tumours represent a rare but important cause of recurrent hypoglycaemia in adults. This case highlights the need to consider proinsulin measurement when insulin and C-peptide levels are not diagnostic, despite clear fulfilment of Whipple’s triad. Early recognition of this biochemical profile facilitates timely localisation and surgical management, which remains the definitive treatment. Increased awareness of proinsulinomas can prevent diagnostic delay and improve patient outcomes.