Hypoglycemia in response to glucose and glucagon in insulinoma patients with a negative prolonged fast: functional and morphological properties

Is the Size of Insulinoma Predictive for its Endocrine Behavior? An Endoscopic Ultrasound Study

OBJECTIVE

Insulinoma is a rare tumor of the pancreas that can lead to spontaneous hypoglycemia due to excessive insulin secretion. Seventy-two-hour fast is the gold standard for finding the correct diagnosis. Endoscopic ultrasound (EUS) is an established examination method to identify the suspicious lesion. Previous studies correlate the measured size of insulinoma and their endocrine behavior. This study was designed to find a relation between these variables.

METHODS

We took the data of patients who had a histologically confirmed insulinoma after receiving an endoscopic ultrasound in our department. Size and echogenicity were correlated with the endpoint of the 72-hour fast and hormone levels.

RESULTS

A total of 45 patients were identified. Most insulinomas were small with a volume of<2 cm³ (median 1.15 cm³). There was no correlation between the duration of fasting, hormone levels, and the size of the insulinoma. In addition, in a subgroup analysis, no connection could be established between the size of the insulinoma and the amount of insulin released after oral glucose exposure. We found that homogeneous tumors were significantly smaller and had a lower Ki-67 index. Furthermore, there was a tendency towards a shorter duration for the 72-hour fast for the small tumors.

DISCUSSION

This data suggests that the measured size of insulinoma by EUS is not related to the time until termination of the 72-hour fast and measured hormone levels. The echogenicity seems more important, showing that homogenous tumors are an indicator of a higher differentiation, which can result in a shorter duration of the fasting period. The differences in the secretion behavior of the insulinomas could complicate the correlation of size and the 72-hour fast period.

Metastatic insulinoma presenting with post-prandial hypoglycemia

Background/Objective

Patients with an insulinoma, a type of pancreatic neuroendocrine tumor, typically present with fasting hypoglycemia but can rarely present exclusively with postprandial hypoglycemia.

Case Report

A 69-year-old man presented with episodes of postprandial blurry vision, sweating, and confusion for the last 2 years that were becoming more frequent over the last several weeks. Home blood glucose measurements revealed postprandial hypoglycemia (glucose level, 45-70 mg/dL), and symptoms were consistent with the Whipple triad. Continuous glucose monitoring revealed only postprandial hypoglycemia within 2 hours following meals. An outpatient fast was conducted with detectable insulin (6 μIU/mL) and C-peptide (2.0 ng/mL) levels with an elevated proinsulin (20.8 pmol/L) level when the serum blood glucose level dropped to 47 mg/dL (21 hours after the initiation of the fast). A computed tomography scan of the abdomen and pelvis showed a 1.6-cm hyperenhancing lesion in the distal body of the pancreas. He underwent endoscopic ultrasonography with fine-needle aspiration. Pathology revealed a low-grade, well-differentiated, neuroendocrine tumor with lymphovascular invasion and regional lymph node metastases, confirming the diagnosis of a pancreatic neuroendocrine tumor.

Discussion

Exclusive postprandial hypoglycemia is estimated to occur in 6% of the insulinomas. Patients with postprandial hypoglycemia may be initially managed as those with reactive hypoglycemia; however, this case highlights the importance of evaluating for an insulinoma in a patient who has failed treatment for reactive hypoglycemia. This case also demonstrates the importance of including proinsulin levels in that evaluation.

Conclusion

Pancreatic neuroendocrine tumor should be considered in postprandial hypoglycemia, even in the absence of fasting hypoglycemia. Measuring proinsulin levels is essential in the diagnostic workup of insulinoma causing hypoglycemia.

PROINSULIN-PREDOMINANT PANCREATIC NEUROENDOCRINE TUMOR-INDUCED HYPOGLYCEMIA AFTER ROUX-EN-Y GASTRIC BYPASS SURGERY

Objective

To present a case of recurrent hypoglycemia following Roux-en-Y gastric bypass (RYGB) surgery whose etiology was determined to be a proinsulin-predominant pancreatic neuroendocrine tumor (a proinsulinoma).

Methods

A case report along with a brief discussion and review of the pertinent literature is presented.

Results

The patient is a 62-year-old female who presented with symptomatic hypoglycemia 11 years after RYGB surgery. Initial workup revealed low insulin levels with elevated proinsulin levels. A 72-hour fast confirmed the presence of proinsulin-induced hypoglycemia secondary to a pancreatic neuroendocrine tumor (PNET). She underwent distal pancreatectomy with splenectomy and a PNET tumor was successfully removed with resolution of her symptoms.

Conclusion

Hypoglycemia after RYGB surgery is a well-established syndrome. While there are several etiologies for this, PNETs (including proinsulinomas) should be considered in the differential diagnosis in this population. Proinsulinomas are an increasingly recognized cause of hypoglycemia. Proinsulin levels must always be included as part of the workup of hypoglycemia in an adult.

Diagnostic Performance of 48-Hour Fasting Test and Insulin Surrogates in Patients With Suspected Insulinoma

OBJECTIVES

This study aimed to evaluate the usefulness of the 48-hour fasting test and insulin surrogates followed by a glucagon stimulatory test (GST) for the diagnosis of insulinoma.

METHODS

Thirty-five patients with suspected insulinoma who underwent 48-hour fasting test and GST were retrospectively included in our study: 15 patients with surgically proven insulinomas and 20 patients in whom insulinoma was clinically ruled out. We determined the duration of the fasting test, plasma glucose levels, serum levels of immunoreactive insulin and C-peptide, and insulin surrogates (serum levels of β-hydroxybutyrate, free fatty acid, and response of plasma glucose to intravenous glucagon [ΔPG]) at the end of the fast.

RESULTS

The sensitivity and specificity of the 48-hour fasting test were 100.0% and 80.0%, respectively, for the diagnosis of insulinoma. When the 48-hour fasting test and immunoreactive insulin, C-peptide, or insulin surrogates were combined, the combination with GST showed the best results. The sensitivity, specificity, and accuracy rate were 93.3%, 95.0%, and 94.3%, respectively, with 1 false-negative case and 1 false-positive case occurring.

CONCLUSIONS

A more accurate and less invasive diagnosis of insulinoma was possible by combining the 48-hour fasting test with the GST, compared with the existing method.

Presentation, diagnostic features and glucose handling in a monocentric series of insulinomas

BACKGROUND

New aspects have emerged in the clinical and diagnostic scenarios of insulinoma: current guidelines have lowered the diagnostic insulin threshold to 3 μU/ml in the presence of hypoglycemia (<55 mg/dl); post-prandial hypoglycemia has been reported as the only presenting symptom; preexisting diabetes mellitus (DM) was recognized in some patients.

AIM

To evaluate clinical features, diagnostic criteria and glucose metabolic profile in a monocentric series of patients affected by insulinomas including two subgroups: sporadic and multiple endocrine neoplasia type-1 syndrome (MEN-1).

SUBJECTS AND METHODS

Clinical, pathological and biochemical data regarding 33 patients were analyzed.

RESULTS

following the current guidelines the 72-h fasting test was initially positive in all cases but one. In this case the test, initially negative, became positive after a 2-yr follow-up. Nadir insulin level was ≥ 3 μU/ml but <6 μU/ml in 3 patients and ≥ 6 μU/ml in the remaining 30 cases. At presentation, 27 patients (82%) reported only fasting symptoms, 3 (9%) only post-prandial and 3 (9%) both. Seven cases (21%) had previously been affected by type 2 DM or impaired glucose metabolism.

CONCLUSIONS

In our series the new cut-off of insulin increased the sensitivity of the 72-h fasting test from 87% to 97%. The absence of hypoglycemia during the test cannot definitively rule out the diagnosis and the test should be repeated in every highly suspicious case. Post-prandial hypoglycemia can be the only presenting symptom. DM may be associated with the occurrence of insulinoma. So that a possible diagnosis of insulinoma must not be ignored if previous impaired glucose handling is evident.

Increased plasma β-hydroxybutyrate levels during the fasting test in patients with endogenous hyperinsulinaemic hypoglycaemia

OBJECTIVE

The objective of the present study was to determine whether a plasma β-hydroxybutyrate (BOHB) level >2700 μmol/l during the 72-h fasting test is sufficient to rule out the diagnosis of endogenous hyperinsulinaemic hypoglycaemia (EHH).

RESEARCH DESIGN AND METHODS

We retrospectively studied BOHB levels in 39 patients with EHH who had undergone a 72-H fasting test to make the diagnosis of EHH, and we compared EHH patients with BOHB levels 2700 MOL/L (group 1), EHH PATIENTS with BOHB levels 2700 MOL/L (group 2) and 59 controls (median glycaemia: 3.2  mmol/l and median BOHB: 6095 μmol/l).

RESULTS

During a 72-h fasting test, nine patients (group 1) had BOHB levels >2700  μmol/l (median 6140 and range 2957-7824) and 30 patients (group 2) had BOHB levels <2700 μmol/l (median 542 and range 0-2607). In group 1, four patients had undergone partial pancreatectomy previously and were evaluated for the recurrence of hypoglycaemia, whereas none of the group 2 patients had been operated. The duration of the fasting test was longer in group 1 than in group 2 (P<0.0001), and at the end of the fasting test, plasma glucose concentrations were not significantly different (P=0.0617), but insulin (P=0.004), C-peptide (P=0.0015) and proinsulin (P=0.0038) levels were significantly lower in group 1 patients than in group 2 patients, suggesting lower insulin secretion and/or impaired glycaemic counter-regulation.

CONCLUSION

During a fasting test, a BOHB level >2700 μmol/l is observed in some EHH patients, suggesting that BOHB levels cannot rule out the recurrence of EHH, in particular, after partial pancreatectomy.

Asymptomatic insulinoma: a case report and autopsy series

AIMS

We investigated the prevalence and characterization of asymptomatic pancreatic tumors in response to our experience of asymptomatic insulinoma.

METHODS

A patient with a moderately low glucose level and pancreatic incidentaloma detected by CT was examined. Pancreas specimens from 423 autopsy cases were also pathologically examined systematically by hematoxylin-eosin staining.

RESULTS

The examined patient showed no profile characteristic of insulinoma by fasting or loading tests, however, ASVS led to diagnosis of insulin-producing tumor. The tumor was resected with the pancreatic body and tail and revealed to be 10 mm in diameter, with 98.5% of the cells positive for insulin. Pathological evaluation confirmed a well-differentiated endocrine pancreatic tumor, which was suggestive of an incidentally detected asymptomatic insulinoma. Microscopic evaluations of pancreatic specimens from 423 autopsy cases revealed pancreatic monotonous lesions in 6 cases (1.42%). In 4 autopsy specimens large enough for immuno-histochemical evaluation, the lesions were positive for glucagon but negative for insulin.

CONCLUSIONS

As concerns the present study, retrospective immunohistochemical investigation in autopsy cases revealed the presence of asymptomatic glucagonoma but no asymptomatic insulinoma. Advances in diagnostic imaging, however, might raise the probability of detecting early asymptomatic stages of insulinoma incidentally. ASVS appears to be sensitive even for asymptomatic incidental insulinomas.

[Endogenous hyperinsulinism: review and follow-up of 24 cases]

Hypoglycemia due to endogenous hyperinsulinism (EH) is diagnosed in a symptomatic patient with low levels of plasma glucose concomitant with elevated plasma insulin and C-peptide. Causes of EH are pancreatic islet-cells disease, use of insulin secretagogues, and autoimmune hypoglycemia. In this review, the authors studied 24 patients with hypoglycemia due to endogenous hyperinsulinism in order to describe aspects of diagnosis and treatment. Our study demonstrated that after 12 hours of fasting (mini-fasting test; at least three samples), all patients presented the diagnostic criteria for EH. Additionally, we found that 11 of 12 patients (91.7%) who underwent glucagon test achieved glucose levels less than 50 mg/dL and below baseline after 120 minutes. Mini-fasting (3 samples) and glucagon test may be useful to prevent prolonged fasting test to clarify the diagnosis of endogenous hyperinsulinism.

Pancreatic Insulinoma Presenting with Postprandial Hypoglicemias

We report the case of an obese 58 years old patient evaluated for hypoglycemia. The response to a prolonged fasting test was normal, but symptomatic hypoglycemia ensued after mixed meals and with oral glucose loading. A magnetic resonance scan of the abdomen revealed a pancreatic tail tumor, histologically diagnosed as benign insulinoma after successful laparotomy. "Glucose-responsive" insulinomas, although rare, have been previously described in the literature. Therefore, the diagnosis of insulinoma should also be considered in patients that exhibit postprandial rather than fasting hypoglycemia.

Secular trends in the presentation and management of functioning insulinoma at the Mayo Clinic, 1987-2007

OBJECTIVE

The objective of the study was to assess changes in the presentation and diagnostic and radiological evaluation of patients with surgically confirmed insulinoma at the Mayo Clinic 1987-2007.

METHODS

A retrospective analysis of patients with insulinoma was conducted. Patients with prior gastric bypass were excluded.

RESULTS

A total of 237 patients [135 women (57%)] were identified. Hypoglycemia was reported solely in the fasting state in 73%, the fasting and postprandial state in 21%, and exclusively postprandially in 6%. There was a predominance of men in the postprandial symptom group. Considering the period of study by quartile, outpatient evaluation increased from 35 to 83% and successful preoperative localization improved from 74 to 100% comparing the first to the fourth quartiles. Although the rates of localization by noninvasive techniques remained static at approximately 75%, the addition of invasive modalities has resulted in successful preoperative localization in all patients in the past 10 yr. The sensitivity and specificity of the established diagnostic criteria using insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and glucose response to iv glucagon were greater than 90% and greater than 70%, respectively.

CONCLUSIONS

Although fasting hypoglycemia is characteristic of patients with insulinoma, postprandial symptoms have been reported with increasing, albeit low, frequency. Trends in the evaluation and preoperative management include a shift to outpatient diagnostic testing, an emphasis on successful preoperative localization to avoid blind pancreatic exploration, and a validation of the diagnostic criteria for hyperinsulinemic hypoglycemia.

Continuous glucose monitoring in patients with insulinoma

BACKGROUND

Insulinomas are rare neuroendocrine tumours that are usually small and may take time to localize. They cause recurrent life-threatening spontaneous hypoglycaemia. Recurrent hypoglycaemia causes loss of hypoglycaemia awareness, putting the patient at further risk, but this has rarely been described in insulinoma. We describe the utility of continuous glucose monitoring (CGM) in patients with insulinoma.

PATIENTS AND METHODS

Three patients, aged 72 years (patient 1), 37 years (patient 2) and 24 years (patient 3), with suspected insulinoma attended our investigation unit, in a university teaching hospital. Biochemical diagnosis was confirmed by elevated plasma insulin and C-peptide during biochemical hypoglycaemia [plasma glucose < 2.2 mM (40 mg/dl)]. Surgery confirmed histology in all. CGM was used to monitor frequency and time of hypoglycaemia during diagnosis and medical treatment, and after definitive surgical treatment.

RESULTS

All patients had evidence of hypoglycaemia unawareness. At diagnosis in patients 1-3, CGM revealed 6.1%, 21.9% and 71.0% of time spent in moderate hypoglycaemia (plasma glucose 2.2-3.0 mM), and 1.4%, 11.4% and 48.1% of time in severe hypoglycaemia (plasma glucose < 2.2 mM), respectively. On diazoxide this reduced to 0.6%, 5.4% and 5.7% time in moderate hypoglycaemia, and no severe hypoglycaemia in patients 1 and 3, and 0.5% in patient 2. Octreotide therapy in patients 2 and 3 resulted in 5.8% and 0% of time in moderate hypoglycaemia, respectively, and no severe hypoglycaemia. After surgical excision CGM confirmed cure in all.

CONCLUSIONS

CGM in insulinoma is useful in detecting hypoglycaemia, and hypoglycaemia unawareness, monitoring response to medical therapy and for confirming cure postoperatively, and is useful in the management of this uncommon but dangerous condition.

Endocrine pancreatic tumors: diagnosis and treatment

Endocrine pancreatic tumors (EPTs) are uncommon, having an incidence of one per 100,000 people. They may appear as sporadic tumors or be associated with hereditary syndromes. EPTs are categorized as functioning or nonfunctioning tumors, based on the presence or absence of clinical syndromes. Among the former, insulinomas and gastrinomas are the most common. For the histopathological investigation of EPTs, chromogranin A and synaptophysin immunostainings are recommended. Measurement of circulating chromogranin A is also the cornerstone for the biochemical diagnosis of these tumors. Furthermore, specific hormones produced and released by the neoplastic cells can be identified by immunostaining and used for biochemical evaluation. To locate EPTs, both noninvasive (ultrasonography, computerized tomography, MRI and radionuclear imaging) and invasive techniques (arterial stimulation with venous sampling) can be used. Debulking procedures (surgery, radiofrequency ablation, embolization/chemoembolization and liver transplantation) and/or medical treatment (chemotherapy, biotherapy and peptide receptor radionuclide therapy) are the options available for the treatment of EPTs. Understanding the molecular events underlying the pathobiology of EPTs will aid the development of more accurate diagnostic/prognostic markers and give guidance for improved therapeutic modalities.

Insulinomas may present with normoglycemia after prolonged fasting but glucose-stimulated hypoglycemia

BACKGROUND

Insulinomas are rare but are the most common cause of hyperinsulinemic hypoglycemia in the adult population. Diagnosis of this pathology relies on clinical features along with laboratory tests and imaging investigations to aid in localization. One of the most robust standard tests used for establishing a biochemical diagnosis is the prolonged (72 h) fast. Currently, it is recommended that a prolonged supervised fast be performed, at least for 48 h if not for 72 h, and many would take the absence of hypoglycemia after a 72-h fast as evidence excluding the diagnosis.

METHODS

We employed prolonged fasts and standard glucose tolerance tests, plus imaging studies and surgical pathology, in two patients with suspected insulinomas.

RESULTS

The prolonged 72-h fast was normal in both the patients, whereas in both cases a prolonged oral glucose tolerance test clearly demonstrated the induction of severe hyperinsulinemia followed by significant hypoglycemia. Surgical removal confirmed the presence of insulinomas in each case.

CONCLUSIONS

Although the sensitivity of the 72-h fast is high and still plays an important role in the diagnosis of an insulinoma, we suggest that a "normal" test result should be interpreted in the light of clinical symptoms.