Early Postoperative Fasting Serum Glucose Levels are Useful in Depicting Future Diabetes Mellitus in Patients with Curative Insulinoma Surgery

BACKGROUND

Hyperglycemia has been reported in some patients after curative insulinoma resection but no systematic investigation of glucose metabolism has been shown in a larger cohort of these patients. Therefore, it is still unknown, whether long lasting hyperinsulinism in insulinoma patients induces insulin resistance, which may jeopardize the postoperative health status of these patients.

METHODS

Early postoperative fasting serum glucose levels were measured in all insulinoma patients after curative tumor resection during the first 48 h, being operated between 2011 and 2018, retrospectively.

RESULTS

Of 77 (100%) patients with benign, spontaneous occuring insulinoma 51 (66.2%) patients were operated on by tumor enucleation. In 15 (19.5%) patients a left pancreatic resection was performed and in 11 (14.3%) patients the pancreatic head or the middle console of pancreatic corpus were excised. In 32 (41.6%) cases the highest fasting postoperative glucose levels were measured between 140-200 mg/dl. In 16 (20.8%) patients the glucose serum levels reached values above 200 mg/dl and in 4 (5.2%) patients short term substitution with insulin was indicated. Only one (1.3%) of these patients developed diabetes mellitus with the need of ongoing insulin treatment. Major postoperative complications were registered in 31 of all 77 patients (40.3%) and in 9 of 16 patients (56.3%) with postoperative glucose levels above 200 mg/dl. This difference was not statistically significant.

CONCLUSIONS

Early postoperative (first 48 h) fasting serum glucose levels in insulinoma patients showed significant hyperglycemia above 200 mg/dl in only few patients (20.8%) and chronic postoperative Diabetes mellitus developed in only one of 77 patients (<2%). Therefore, recovery of glucose metabolism after insulinoma resection is fast and medical intervention is not mandatory in most of these patients.

Differentiation of insulin secretion patterns in insulinoma

BACKGROUND

In patients with insulinoma, biochemical proof of inappropriately elevated insulin secretion during hypoglycemia is required prior to surgery. Because circulating insulin levels usually vary widely, we have used the combined OGTT-fasting test to define new normative criteria for a retrospective systematic analysis.

METHODS

We retrospectively analyzed insulin concentrations from OGTT-fasting tests of 64 patients with surgically removed insulinomas. In addition, the response to intravenous somatostatin infusions was estimated. Normative criteria were defined to obtain comparable estimates of insulin concentrations: basal, glucose-stimulated maximum, postglucose plateau, and secretory bursts.

RESULTS

Three types of insulin secretion patterns were identified: (1) the autonomous secretion pattern (type 1, N=17) with basal and post-OGTT plateau insulin concentrations of approximately 50 mU/L, suppression after OGTT by 41%, virtual absence of distinctive secretory bursts, and resistance to somatostatin-mediated suppression (25 %); (2) the inadequate suppression pattern (type 2, N=28) with moderately elevated basal and post-OGTT insulin concentrations of approximately 20 mU/L, suppression after OGTT by 73%, absence of secretory bursts, and incomplete somatostatin-induced suppression (56 %); (3) the late-burst secretion pattern (type 3, N=19) with similar basal and post-OGTT insulin concentrations of 17 mU/L, suppression after OGTT by 76%, true insulin bursts of Delta 13+/-11 mU/L (184%), and nearly complete somatostatin-induced suppression by 64%.

CONCLUSIONS

By means of a new normative analysis of the combined OGTT-fasting test, three different patterns of insulin secretion can be described in patients with insulinoma: the autonomous secretion type, the inadequate suppression type, and the late-burst secretion type.

A new classification plot for the C-peptide suppression test

CONTEXT AND OBJECTIVE

To evaluate the C-peptide suppression test as a screening test in patients with symptoms of hypoglycemia as compared to the standard fasting test.

DESIGN

Retrospective discriminant analysis of data from C-peptide suppression tests.

SETTING

Clinical study.

PATIENTS

Patients with insulinomas and patients without insulinomas but having symptoms compatible with hypoglycemia.

INTERVENTIONS

The results from C-peptide suppression tests of 26 patients with insulinomas and 100 patients without insulinomas were compared.

MAIN OUTCOME MEASURES

A classification plot which introduces two discriminant parameters for the C-peptide suppression test: the ratio of [blood glucose]/[C-peptide] at the lowest C-peptide concentration and mean glycemia during insulin infusion.

RESULTS

In patients with insulinomas, minimal serum C-peptide levels were higher (1.81+/- 0.87 ng/mL; median 1.83 ng/mL; maximal suppression 37 +/- 24% of basal C-peptide levels) as compared to patients without insulinoma (0.40 +/- 0.15 ng/mL; median 0.30 ng/mL; maximal suppression of 75 +/- 9%; P<0.001). Mean glycemia during the test was lower in patients with insulinomas (30.8 +/- 3.3 vs. 47.5 +/- 8.3 mg/dL; P<0.001) as was the [blood glucose]/[C-peptide] ratio (21.9 +/- 14.6 vs. 139.2 +/- 43.8; P<0.001). Discriminant analysis revealed a specificity of 96% to rule out the diagnosis of 'insulinoma' at a 1% probability threshold with a sensitivity of 100%.

CONCLUSIONS

We developed a new classification plot for the C-peptide suppression test in order to accurately identify those patients whose symptoms of hypoglycemia are not due to endogenous hyperinsulinemia/insulinomas. Thus, the need for fasting tests and hospitalization costs can be reduced.