Endocrine Abstracts

Case report: A 47-year-old lady presented to the Emergency Department (ED) with an episode of dizziness, sweating and palpitations. On ambulance arrival CBG was low at 2.2 mmol/l, and symptoms resolved after treatment of hypoglycaemia. She had first noticed these symptoms eight years ago when fasting for Ramadan. However over the past two years she had experienced episodes multiple times per day, relieved by sugary food or drinks. She occasionally woke at night with symptoms but there was no specific correlation with time or meals. She had gained 20 kg weight unintentionally over the past two years. Systems review was unremarkable. Past medical history was significant for depression, treated with sertraline 50 mg. She took no other medications or supplements and denied insulin or sulphonylurea use. There was a strong family history of type 2 diabetes mellitus (father, paternal grandfather and uncle). She was unemployed and did not consume alcohol or recreational drugs. On arrival in ED observations were unremarkable with a CBG of 5 mmol/l. There were no clinical signs of endocrinopathy and examination was unremarkable. Further investigations showed a 9 AM cortisol of 568 nmol/l and HbA1 C 38 mmol/mol. Sertraline was stopped. An inpatient 72 hour fast elicited hypoglycaemia at 60 hours. Lab results confirmed hypoglycaemia (1.8 mmol/l) with inappropriately normal C-peptide 709 pmol/l (366-1465 pmol/l) and insulin 76 pmol/l (21-175 pmol/l). Urine sulphonylurea screen was negative. Diazoxide 100 mg t.d.s. was commenced. Freestyle LibreView 2 sensor was supplied and demonstrated improvement in hypoglycaemia, to a glucose range of 6-11 mmol/l. CT pancreas showed no pancreatic lesions. Gallium-68 DOTATATE scan showed no avid lesions. She is currently awaiting endoscopic ultrasound (EUS) for further work-up.

Discussion: The most likely diagnosis in this case is insulinoma, a rare but important condition. Diagnosis is frequently delayed, as in this case, due to the non-specific presenting symptoms. A careful history and investigation is required, with biochemical confirmation of inappropriate endogenous insulin secretion must be sought before proceeding to imaging. Biochemistry demonstrates raised or inappropriately normal C-peptide and insulin at the time of hypoglycaemia. Differential diagnoses of this biochemical picture including sulphonylurea intake, nesidioblastosis and insulin autoantibodies. Most cases are benign and surgical treatment is generally very effective, but this case highlights the challenges in localising a surgical target. CT pancreas has a sensitivity of around 54% (1) and even EUS only 81% (2). Arterial calcium stimulated venous sampling may be required in particularly elusive cases.

References: 1. Yang Y, Shi J, Zhu J. Diagnostic performance of noninvasive imaging modalities for localization of insulinoma: A meta-analysis. Eur J Radiol. 2021 Dec;145:110016.2. Wang H, Ba Y, Xing Q, Du JL. Diagnostic value of endoscopic ultrasound for insulinoma localization: A systematic review and meta-analysis. PLoS One. 2018 Oct 23;13(10).