Glucagonoma, a pancreatic neuroendocrine tumour, is often diagnosed in later stages due to its rarity and non-specific symptoms. Early diagnosis is essential as pancreatic resection is the only curative treatment. 80% of glucagonoma cases present with new-onset or worsening control of diabetes. The clinical overlap between hyperglycaemia due to glucagon excess and the features of diabetes contributes to diagnostic delay. We present this case of a middle-aged man with clinical manifestations of glucagonoma, on the background of long-standing Type 2 diabetes mellitus.
The manifestations of glucagonoma, as experienced by this patient, includes worsening glycaemic control, chronic diarrhoea, anaemia, depression, mouth ulcers and 4kg of unintentional weight loss in 6 months.
The focus of the patient’s work-up was for causes of diarrhoea. Colonoscopy and capsule endoscopy were unremarkable. Abdominal computer tomography (CT) scan incidentally detected
a 20mm lesion on the pancreatic tail and an 8mm lesion on the uncinate process. 68Ga-DOTA-octreotate (GaTate) PET/CT scans revealed high somatostatin-receptor expression in both lesions, alongside further sub-centimetre DOTA-avid foci in the uncinate process, consistent with neuroendocrine tumours (NET). There was no evidence of loco-regional nodal or metastatic spread. The pancreatic tail tumour was classified on biopsy as a well-differentiated grade-1 NET (Ki-67=2%). Glucagon was (507 pg/mL, 140) and chromogranin A was (127 ng/L, 39). MEN1 genetic testing returned negative. After initial monthly subcutaneous lanreotide, a distal pancreatectomy and splenectomy was undertaken. Furthermore, the uncinate process NETs were resolved with several rounds of radiofrequency ablation. Currently the patient is in remission and under surveillance with 6-monthly PET scans.
The aim of this case report is to demonstrate the challenges of diagnosing patients with glucagonoma in the context of underlying diabetes or metabolic syndrome. We aim to highlight “red flags” of gastrointestinal and constitutional symptoms to prompt investigation of rarer causes of hyperglycaemia such as glucagonoma.