Insulin-Producing Tumors: Rare, Often Misdiagnosed

It's an uncommon condition—many physicians never see a case in their lifetime. And insulinoma, which is an insulin-secreting tumor of the pancreas gland, can be very difficult to diagnose, says Jerome V. Tolbert, MD, Ph. D., medical director of the Outreach Team for the Friedman Diabetes Institute at Beth Israel Medical Center in New York City.

Telltale signs that you may have such a tumor?

"If you have a high insulin level and yet a low blood sugar over time, you could have insulinoma," Tolbert says.

In a typical case of insulinoma, which is part of a larger category called islet cell tumors, insulin is produced even when it is not needed.

"This is a tumor in the kind of cell that makes insulin, and as a result, people have excess insulin in their body," explains John Chabot, MD, executive director of the Pancreas Center and chief in the Division of GI/Endocrine Surgery at NewYork-Presbyterian/Columbia University Medical Center in New York City.

The hallmark of diagnosis, he says, is severe hypoglycemia to the point where the patient is at risk for fainting or having seizures.

"It's such a unique tumor that while every doctor knows about insulinoma, he probably won't see anyone with the condition throughout their career," he says.

In a healthy person, the body produces insulin when it's needed and stops producing it when there is no need, Tolbert explains. But with an insulinoma, there's no shut-off in insulin production. "Obviously it's very important to diagnose this tumor," he says.

The method for detecting such a tumor is rather unpleasant for the patient, who becomes extremely hungry, Tolbert says. Typically, he explains, the patient is hospitalized for three days without being given food.

"After three days without eating, the person should have a very low blood sugar level," he says. And since there's no sugar that needs insulin to turn it into usable energy, it would be expected that the insulin level would also be low. But with insulinoma, the person continues to have a high insulin level, Tolbert explains.

When a doctor is suspicious, diagnostic tests are performed to try to localize the tumor. Sometimes the tumors can be tricky to find. The doctor may order a CAT scan, an MRI, or an endoscopic ultrasound, Chabot says. Treatment consists of surgical removal of the tumor, he says.

Fortunately, such treatment is usually effective. "There is a very good success rate and the recurrence rate of these tumors is very low," Chabot says.