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Open access

Seong Keat Cheah, David Halsall, Peter Barker, John Grant, Abraham Mathews, Shyam Seshadri and Singhan Krishnan

Summary

A frail 79-year-old lady with dementia presented with a 2-year history of frequent falls. Recurrent hypoglycaemic episodes were diagnosed and treated with continuous glucose infusion in multiple hospital admissions. Hypoadrenalism and hypothyroidism were ruled out. Whilst hypoglycaemic (blood glucose 1.6 mmol/L), both plasma C-peptide and proinsulin concentrations, were inappropriately elevated at 4210 pmol/L (174–960) and >200 pmol/L (0–7) respectively with plasma insulin suppressed at 12 pmol/L (0–180). Whilst reported cases of proinsulinoma are typically pancreatic in origin, radiological investigations of the pancreas in this patient did not identify abnormalities. Unexpectedly contrast CT identified a heterogeneously enhancing mass (6.6 cm) at the lower pole of the left kidney consistent with renal cell carcinoma. Non-islet cell tumour-induced hypoglycaemia has been associated with renal malignancy; however, a serum IGF2:IGF1 ratio measured at <10 effectively excludes this diagnosis. Concomitantly on the CT, extensive peripherally enhancing heterogeneous mass lesions in the liver were identified, the largest measuring 12 cm. A palliative approach was taken due to multiple comorbidities. On post-mortem, the kidney lesion was confirmed as clear cell renal carcinoma, whilst the liver lesions were identified as proinsulin-secreting neuroendocrine tumours. In conclusion, the diagnosis of proinsulinoma can be missed if plasma proinsulin concentration is not measured at the time of hypoglycaemia. In this case, the plasma insulin:C-peptide ratio was too high to be accounted for by the faster relative clearance of insulin and was due to proinsulin cross-reactivity in the C-peptide assay. In addition, the concomitant malignancy proved to be a challenging red herring.

Learning points:

  • Even in non-diabetics, hypoglycaemia needs to be excluded in a setting of frequent falls. Insulin- or proinsulin-secreting tumours are potentially curable causes.
  • Whilst investigating spontaneous hypoglycaemia, if plasma insulin concentration is appropriate for the hypoglycaemia, it is prudent to check proinsulin concentrations during the hypoglycaemic episode.
  • Proinsulin cross-reacts variably with C-peptide and insulin assays; the effect is method dependent. In this case, the discrepancy between the insulin and C-peptide concentrations was too great to be accounted for by the faster relative clearance of insulin, raising the suspicion of assay interference. The C-peptide assay in question (Diasorin liaison) has been shown to be 100% cross reactive with proinsulin based on spiking studies with a proinsulin reference preparation.
  • Whilst reported cases of proinsulinoma and 99% of insulinomas are of pancreatic origin, conventional imaging studies (CT, MRI or ultrasound) fail to detect neuroendocrine tumours <1 cm in 50% of cases.
  • The concomitant renal mass identified radiologically proved to be a red herring.
  • In view of the rarity of proinsulinoma, no conclusive association with renal cell carcinoma can be established.
Open access

Chad Bisambar, Andrew Collier, Fraser Duthie and Carron Meney

Summary

A 40-year-old Caucasian female presented with hyperglycaemia, polyuria, polydipsia and weight loss of 6 kg over a 1-month period. There was no personal or family history of malignancy or diabetes mellitus. On examination, she was jaundiced with pale mucous membranes and capillary glucose was 23.1 mmol/L. Initial investigations showed iron deficiency anaemia and obstructive pattern of liver function tests. HbA1c was diagnostic of diabetes mellitus at 79 mmol/mol. Malignancy was suspected and CT chest, abdomen and pelvis showed significant dilatation of intra- and extra-hepatic biliary tree including pancreatic duct, with periampullary 30 mm mass lesion projecting into lumen of duodenum. Enlarged nodes were seen around the superior mesenteric artery. This was confirmed on MRI liver. Fasting gut hormones were normal except for a mildly elevated somatostatin level. Chromogranin A was elevated at 78 pmol/L with normal chromogranin B. Duodenoscopy and biopsy showed possible tubovillous adenoma with low-grade dysplasia, but subsequent endoscopic ultrasound and biopsy revealed a grade 1, well differentiated neuroendocrine tumour. The patient was started on insulin, transfused to Hb >8 g/dL and Whipple’s pancreatico-duodenectomy was undertaken. This showed a well-differentiated neuroendocrine carcinoma arising in duodenum (Grade G1 with Ki67: 0.5%), with areas of chronic pancreatitis and preservation of pancreatic islet cells. There was complete resolution of diabetes post Whipple’s procedure and patient was able to come of insulin treatment. Her last HBA1C was 31 mmol/mol, 4 months post tumour resection.

Learning points:

  • Diabetes mellitus and malignancy can be related.
  • A high index of suspicion is needed when diabetes mellitus presents atypically.
  • Non-functional neuroendocrine tumours can present with diabetes mellitus.