Background: Patients with pancreatic tumors that induce hypoglycemia present with a myriad of symptoms. Laboratory testing can frequently result in data challenging to the clinician to confirm the biochemical diagnosis. Proinsulin, in addition to insulin levels, may be essential in evaluating and diagnosing an insulinoma.
Methods: The objective of this case report is to demonstrate the potential importance of proinsulin levels in the evaluation of tumor-induced hypoglycemia. We report a 49-year-old woman with an unusual clinical presentation. Unlike many patients with tumor-induced hypoglycemia, her fasting glucose levels were fairly unimpressive, her insulin levels were undetectable during a prolonged fast, and she had elevated proinsulin levels.
Results: The inpatient fast was remarkable for levels of serum glucose 53 mg/dl or higher, a serum insulin <2 uIU/ml, C-peptide 0.7-1.1 (nl 0.8-3.1 ng/ml), and proinsulin 29.2-36.8 pmol/l (nl < or = 18.8 pmol/l). CT scanning of the abdomen revealed multiple pancreatic lesions. A laparoscopic distal pancreatectomy led to the removal of multiple neuroendocrine tumors, which stained only for proinsulin and not for other pancreatic tumor markers. Postoperatively, she normalized her biochemical serum studies and has remained symptom-free 2 years later.
Conclusions: The measurement of proinsulin plays an important part in the diagnostic workup of neuroendocrine tumors causing hypoglycemia. These potentially malignant tumors can be treated adequately with minimally invasive surgery.