Endocrine Abstracts

Introduction: Insulinomas are the most common functioning endocrine neoplasms of the pancreas. 53% of patients are diagnosed within five years of experiencing their first symptoms. Surgical resection is the primary treatment modality. However, patients awaiting surgery or who are not surgical candidates have achieved symptomatic relief from medical therapy. Cases of insulinoma masking diabetes has been described but are rare and diabetes often presents following surgery. Here, we describe a case of insulinoma diagnosed four years after symptom onset with unmasking of type 2 diabetes mellitus following initiation of medical treatment.

Clinical case: An 89-year-old woman presented with severe hypoglycaemia, having been found by relatives in bed with neuroglycopenic symptoms. Capillary blood glucose was 1.4 mmol/l. She was given intramuscular Glucagon by paramedics. Upon further questioning, the patient reported having one to two similar episodes of hypoglycaemia per month over the past four years, which she was self-correcting at home or by help of the ambulance service. Pituitary, liver and renal profiles were within normal limits. During the admission, the patient underwent a prolonged fasting test. Although nadir blood glucose achieved was 2.5 mmol/l due to significant symptom, hypoglycaemia screen revealed high level of C-peptide 2885 pmol/l (370-1470) though normal insulin (64 pmol/l) and beta-hydroxybutyrate levels (0.1 mmol/l) at hypoglycaemia episode. CT pancreas revealed a 14.5 mm enhancing nodule on the body of the pancreas consistent with a neuroendocrine tumour, which was confirmed by MRI imaging. After discussion at the MDT, the patient was started on diazoxide 50 mg TDS. A dotatate-PET scan was arranged, and she was listed for surgery. Blood glucose was in range after starting diazoxide. However, the patient was readmitted after one month with hyperglycaemia (37.1 mmol/l), fever, cough, and bilateral pitting oedema. Diazoxide was held and she was commenced on oral antihyperglycaemic agents, and then eventually switched to insulin management. Unfortunately, the patient deteriorated during the admission and passed away.

Discussion: Our case highlights the challenges with the diagnosis of insulinoma and how insulinoma can mask undiagnosed type 2 diabetes. This also highlights the importance of continuing glucose monitoring after starting medical management for insulinoma, even if stable glycaemia has been initially achieved.