Endocrine Abstracts

A 42 year old lady presented to the Endocrinology clinic with a longstanding history of exertional dizziness, increasing in frequency over the preceding two months. She reported marginal symptomatic improvement with the introduction of frequent carbohydrate rich meals. She was asymptomatic in the post-prandial period. She had no associated nausea, confusion, palpitations, diaphoresis, collapse or weight gain. She was on medication (SSRI) for anxiety. Her father and paternal grandmother both had successful pancreatic surgeries for treatment of insulinoma. Biochemical evaluation in clinic revealed random plasma glucose of 2.7 mmol/L (asymptomatic), HbA1c of 24 mmol/mol, and no evidence of pituitary, liver or thyroid dysfunction. A synacthen test was normal. The impression was that this lady had clinical evidence of an insulinoma. She was admitted for a 72-hour fast. During the 72-hour fast the patient remained haemodynamically stable and asymptomatic despite plasma glucose levels being persistently below 3 mmol/l. The fast was terminated at hour 55 due to the patient developing an episode of symptomatic neuroglycopenic hypoglycaemia with plasma glucose of 2.2 mmol/l. The patient recovered after administration of IV glucagon with plasma glucose of 3 mmol/l at 5 min post-injection, and 5 mmol/l 50 min post-injection. When the patient was symptomatically hypoglycaemic and had plasma glucose levels of 2.2 mmol/l, the insulin level was 43.8 pmol/l with a C-peptide level of 463 pmol/l. Growth hormone, IGF1 and proinsulin levels were normal. A sulphonylurea screen was negative. A beta hydroxybutyrate level was mildly elevated at 1070 umol/l. Overall the biochemistry was consistent with endogenous hyperinsulinaemia. Preliminary imaging on this patient failed to localise the site of the insulinoma. CT scan of the abdomen and pelvis and MRI of the liver and pancreas were normal. There was no evidence of abnormal radioisotope uptake on planar and SPECT CT octreotide scintigraphy of the thorax, abdomen and pelvis. Endoscopic ultrasonography is pending. If there remains difficulty localising the insulinoma, a selective arterial calcium stimulation test with hepatic venous sampling and/or PET scanning with either Gallium or GLP-1 will be considered. The patient’s father previously tested negatively for the MEN-1 gene mutation. Insulinomas are rare neuroendocrine tumours with an incidence of 1-4/1,000,000. In 5% of cases, insulinomas are associated with the MEN-1 genetic mutation. The percentage association of insulinomas with MEN-4 has not yet been defined. This is an interesting case of a likely familial insulinoma with to-date no association with MEN-1 syndrome. We await the results of repeat MEN-1 testing and MEN-4 testing.