This is a result of a tumour of the APUD cells of the islets of Langerhans. The majority of these APUD tumours are benign
- more than 90% of insulinomas are benign and generally present as small, well-encapsulated solitary tumours
- 7-8% of insulinoma patients have MEN-I syndrome (insulinomas occur in 21% of MEN-I patients)
- clinical features associated with a malignant insulinoma are clinically indistinguishable from those with benign tumours.
Presentation is with episodes of hypoglycaemia, especially when fasting and exercising. Episodes may worsen over time. An increased appetite in combination with frequent food intake has often resulted in a substantial weight gain.
Diagnosis and investigation of insulinomas:
- inappropriate hyperinsulinaemia
- high ratio of proinsulin to insulin in a fasting blood sample (due to defective post-translational processing of proinsulin which allows proinsulin to be secreted in addition to insulin and C-peptide)
- CT scanning and/or pancreatic arteriography to identify the site of the lesion - usually in distal 2/3 of pancreas (occasionally in head of pancreas or ectopic site such as duodenal wall)
Management:
- management is directed by a specialist
- prolonged periods without glucose intake should be avoided by administering frequent meals and/or by continuous glucose infusion either during the night or over the 24 hour period
- somatostatin analogues are of limited use because not all insulinomas express somatostatin receptor subtypes that bind these drugs
- if a solitary insulinoma then surgical removal of the tumour may be curative
- if a metastatic insulinoma then the symptoms of insulin hypersecretion will completely disappear only after complete resection of all the metastases
- combination chemotherapy (with adriamycin and streptozotocin) with and without embolization and chemoembolization have resulted in temporary tumour regression and a remission of symptoms in patients with insulinomas
Reference:
- de Herder WW and Lamberts SWJ. Best Practice & Research Clinical Endocrinology & Metabolism 2004; Volume 18(4): 477-495.