A Case of a Malignant Insulinoma in a Young Adult Woman

Insulinomas are very rare neuroendocrine tumors with an annual incidence of 1-4 cases per million persons years. Most solitary insulinomas are sporadic but can also occur in the setting of multiple endocrine neoplasia type 1. Although uncommon, some have malignant potential. The diagnosis is determined by inappropriate high insulin levels during an episode of hypoglycemia followed by localization of the tumor.

Case Description :

This is a case of a 33-year-old woman with no past medical history that was evaluated due to recurrent episodes of hypoglycemia for 2 years but that had become more severe for the past 2 weeks. She reported episodes occurred mostly at fasting with resolution of symptoms with food intake. She had been eating frequently to avoid hypoglycemia and had gained 31 kg. She described symptoms as tingling of fingers, perioral numbness, and slurred speech. Family history is not suggestive of familial syndromes. She developed a hypoglycemia level 3 and taken to the hospital. Patient was stabilized with dextrose infusion. We decided to hospitalize her for further work-up. While in urgency room, blood glucose (BG) dropped to 30mg/dL with concomitant insulin level of 58µU/mL and c-peptide level in 4.20ng/mL. Sulfonylurea screen was negative. Thyroid function tests normal. Total cortisol in 14.00 µg/dL. Negative insulin antibodies. Biochemical findings were suggestive of insulinoma thus we proceeded to do imaging studies. Initial abdomino-pelvic CT scan was unrevealing of any pathology. An MRI showed a lesion on posterior aspect of pancreatic body tail measuring 1.6x1.1x1.3 cm. Diazoxide was started to aid in symptoms but resulted in side effects such as peripheral edema, hyponatremia, thrombocytopenia, and prolongation of QT segment on ECG. She was fully dependent of dextrose infusion to maintain stable BG. After surgery evaluation she underwent a distal pancreatectomy with splenectomy due to proximity. The pathology was remarkable for a well differentiated neuroendocrine tumor, measuring 1.9x1.8x1.7cm, Ki-67 index less than 3%, no tumor extension and clear margins. There was involvement of one regional lymph node. Post-surgery she had complete resolution of hypoglycemia and have lost 18 kg to date.

Discussion :

Due to the insidious clinical manifestations, the diagnosis of insulinomas can be delayed giving the tumor the potential to transform into malignancy. Malignant insulinomas are rare and few data about their prognosis are available. Insulinomas usually presents during the fifth decade of life; highlighting that a high clinical suspicion and prompt recognition in a young patient is critical for its appropriate management and delay of serious complications.