Insulinoma in a patient with NIDDM.

OBJECTIVE: To confirm insulinoma as the cause of hypoglycemia in a patient with NIDDM and determine the frequency of the co-occurrence of these two conditions.

RESEARCH DESIGN AND METHODS: The patient underwent an in-hospital prolonged fast (< or = 72 h), according to standard protocol, and an ultrasound examination of the pancreas. All cases of histologically confirmed insulinoma at this institution over the period of 1927-1992 were reviewed to determine the prevalence of pre-existent diabetes mellitus.

RESULTS: After 10 h of fasting, plasma glucose was low (1.89 mM); plasma insulin (258 pM) and C-peptide (1.39 nM) were elevated in the absence of sulfonylurea in the plasma. An insulinoma detected by ultrasonography was removed surgically with subsequent reoccurrence of insulin-requiring diabetes. Among 313 cases of insulinoma confirmed at this institution, this patient is the only one with pre-existent diabetes mellitus.

CONCLUSIONS: Insulinoma occurs extraordinarily rarely in patients with pre-existing NIDDM.