Persistent hyperinsulinaemic hypoglycaemia is usually caused by insulinoma in adults and nesidioblastosis in infancy. Nesidioblastosis is a functional beta cell disorder caused by the proliferation of both ductal elements and islet cells, with hypertrophy of beta cells in islets (1). In adults, the pathophysiology of nesidioblastosis remains unclear. There is increasing recognition of nesidioblastosis post gastric bypass surgeries as a cause for post prandial hypoglycaemia (2). The disease can be categorised histologically into diffuse or focal form. In adults, focal disease is exceedingly rare with only 4 cases reported in literature.
We present a case of a 50-year-old truck driver with six months history of unexplained fatigue, dizziness and loss of consciousness prior to driving. His symptoms were relieved by frequent oral intake which resulted in 15kg weight gain. There was documented hypoglycaemia of 2.7mmol/L at the time of loss of consciousness. Biochemical investigation revealed elevated serum fasting insulin of 24 mU/L (0-20 mU/L) and proinsulin of 25.7 pmol/L (< 13.3 pmol/L), and normal c-peptide of 1.4 nmol/L (0.4-1.5 nmol/L). Magnetic resonance imaging demonstrated hyperenhancement in the pancreatic head measuring 15x13mm abutting D2. Ga68 Dotatate positron emission tomography was inconclusive. Contrast enhanced endoscopic ultrasound (EUS) demonstrated a 20mm mass in the uncinate process of the pancreas with contrast uptake. Whipple procedure was successfully performed with resolution of symptoms. Histopathology confirmed focal nesidioblastosis with predominantly beta cells and interestingly a 2mm pancreatic neuroendocrine tumour (NET), grade 1 Ki67 < 2%.
The diagnostic work up is a conundrum. Contrast enhanced EUS was vital to localisation. Differential diagnoses include pancreatic NETs which are a heterogeneous group of islet-cell tumours with a tendency for hormonal production. Whilst insulinomas and proinsulin-secreting NETs have many parallels, focal nesidioblastosis is a discrete entity and should be considered in a patient with presumptive diagnosis of an insulinoma.