Insulinoma presenting as hypoglycemia during lactose tolerance testing: a case report

Insulinoma is a rare functioning pancreatic endocrine tumor, typically presenting as a sporadic solitary lesion causing hypoglycemia. While these tumors can lead to marked autonomic and neuroglycopenic symptoms, the diagnosis is often delayed.

We present a case of a 60-year-old Caucasian man presenting with a 1-year history of progressive episodic confusion and an unexpected finding of symptomatic hypoglycemia during a lactose tolerance test. Further inquiry revealed an 8-year history of more subtle episodic neuroglycopenic symptoms preceding his presentation. After additional biochemical testing suggested a diagnosis of insulinoma, abdominal imaging was performed and revealed a 1.2-cm tumor in the tail of the pancreas. Following laparoscopic resection of the tumor, the patient had complete resolution of his symptoms and maintained normal glucose levels.

The clinical presentation of functioning pancreatic neuroendocrine tumors can be subtle and nonspecific. As such, clinicians should remain vigilant for insulinoma when symptomatic hypoglycemia is present. To our knowledge, this is the first report of an insulinoma found after hypoglycemia was detected during lactose tolerance testing.