Type 2 diabetes mellitus in a patient with malignant insulinoma manifesting following surgery

Abstract

Insulinomas, although they are rare, are the most common of pancreatic islet cell tumours. The incidence is estimated at only four per million person-years and only 5-12% of reported cases are malignant. Distinction between malignant and benign tumours can only be made by the presence of metastasis, as there are no specific morphologic, biochemical or genetic features distinguishing them. Most patients with malignant insulinoma have lymph node or liver metastases and, rarely, bone involvement. The coincidence of insulinoma and diabetes mellitus is an extremely rare condition and reported only in a few cases. We report a 45-year-old woman who was diagnosed with insulinoma on the basis of clinical and laboratory findings and endoscopic examination. Histopathological diagnosis revealed well-differentiated endocrine carcinoma of the pancreas with lymph node metastases. The case was accepted as malignant insulinoma and the patient underwent surgery. Interestingly, hyperglycaemia occurred after the removal of the insulinoma, with the requirement for insulin in the post-operative 3 weeks, which was changed to oral anti-diabetic agents as a permanent treatment. The patient is still being treated with oral anti-diabetic agents. We think that the patient might have had diabetes mellitus, because of insulin resistance that developed with a high-caloric intake stimulated by hypoglycaemia, and which had been masked for many years, but manifested overtly after removal of the tumour. Although this is a rare condition, clinicians should bear in mind that insulinomas may exist together with diabetes mellitus, and it is important to have this suspicion when considering the perioperative approach and for the prevention of morbidities.