Hypoglycemia Unawareness in Insulinoma Revealed with Flash Glucose Monitoring Systems

Insulinoma Unmasked: A Continuous Glucose Monitoring-Fueled Journey

Insulinomas are rare functional neuroendocrine tumors that are usually indolent and small. Due to their rarity, there is often a delay in disease recognition and diagnosis, and small tumor size makes their localization challenging. Glucose monitoring and dietary modification with or without pharmacotherapy are crucial during diagnostics, and surgery is the only definite treatment. Continuous glucose monitoring (CGM) systems can be a valuable tool in managing insulinoma patients. We present three patients with confirmed endogenous hyperinsulinemic hypoglycemia undergoing tumor localization, medical treatment, and surgery while wearing a CGM system. By accurately depicting glucose fluctuations, CGM can help prevent hypoglycemia, decrease hypoglycemia unawareness, track hypoglycemia frequency, aid in medical therapy dose titration, and confirm a cure after surgery.

A case of insulinoma misidentified as schizophrenia due to its manifestation in neuropsychiatric symptoms

Insulinomas can present with neuroglycopenic symptoms suggesting neuropsychiatric disorders, delaying diagnosis and treatment. We recently treated a 65-year-old woman with insulinoma who was misdiagnosed at her nearby psychiatric clinic as having schizophrenia because of personality changes and memory impairment; she was treated with brexpiprazole, which was discontinued due to persistence of the symptoms. Despite her relatively low casual plasma glucose (70 mg/dL), the physician at the psychiatric clinic did not investigate the possibility of hypoglycemia, partly because her HbA1c level (5.2%) was within normal range. After skipping lunch one day, she was found by her family to be unable to communicate properly. She was transported to the emergency room of our hospital, where intermittently scanning continuous glucose monitoring (isCGM) use permitted detection of the hypoglycemia and led to a diagnosis of insulinoma and successful resection. A 72-h fasting test established hyperinsulinemic hypoglycemia. Contrast-enhanced computed-tomography and endoscopic ultrasonography together with selective arterial calcium stimulation test revealed an insulin-secreting tumor in the tail of the pancreas. Surgical resection of the tumor corrected her glucose and insulin levels as well as eliminated the insulinoma neuropsychiatric symptoms. Pathological examination showed that the tumor was positive for chromogranin A, synaptophysin and insulin. It is, therefore, important for physicians to be aware that insulinomas can manifest as neuroglycopenic symptoms and to consider the possibility of hypoglycemia by careful medical interview and isCGM, especially when patients suspected of psychiatric disorders do not show the expected response to antipsychotic drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13340-024-00722-9.

A Case Report: Hypoglycaemic Unawareness Associated With Insulinoma

Hypoglycaemic unawareness (HU) is more frequently described in relation to diabetics in the literature. We have noted that there is also an increasing reporting of HU in insulinoma cases. We report a hospital presentation for an incidental finding of hypoglycaemic unawareness in a gentleman in his fifties who was eventually diagnosed with insulinoma following biochemical studies, radiologic evaluation and histologic evaluation of an excised lesion between the pancreas and the spleen. We have reviewed existing literature evidence regarding the possible aetiologies and management options for this occurrence. More research studies to identify the epidemiology of this association and the determination of a protocol for increased detection of patients with insulinoma who display HU will need to be done.

Insulinoma with Hyperprocalcitoninemia and Hypercalcitoninemia Showing Coexpression of Insulin and Calcitonin in Its Tumor Cells

Neuroendocrine neoplasms can produce multiple hormones that are released into the bloodstream, causing symptoms that vary depending on the type and quantity of hormones involved. We herein report a 63-year-old asymptomatic patient with pancreatic insulinoma who showed marked elevations in circulating calcitonin and procalcitonin levels that returned to normal following surgery. Immunohistochemical analyses confirmed the co-staining of calcitonin and insulin immunoreactivity in the tumor cells, suggesting a calcitonin-producing insulinoma. This insulinoma released calcitonin and a considerable amount of its precursor peptide, procalcitonin, resulting in both hyperprocalcitoninemia and hypercalcitoninemia.

Unmasked insulinoma occasioned by severe hypoglycemic coma immediately postpartum: a case report

BACKGROUND

Insulinoma in women during pregnancy and postpartum is very rare; approximately 65% of cases are diagnosed early in pregnancy and ~ 35% immediately after delivery, few being found in middle or late pregnancy, likely due to increased insulin resistance seen after early-stage pregnancy. We successfully treated a case of insulinoma in which severe hypoglycemic coma immediately after delivery occasioned detailed investigation and diagnosis.

CASE PRESENTATION

Our patient experienced hypoglycemic coma in the 3rd month of pregnancy (initially considered due to her hyperemesis gravidarum) that improved spontaneously during the gestational period. No abnormalities of plasma glucose or body weight were found in regular checkups during her pregnancy; however, recurrence of hypoglycemic coma after delivery led us to suspect insulinoma. While contrast enhanced computer tomography and endoscopic ultrasonography (EUS) initially failed to detect a tumor in the pancreas, selective arterial calcium stimulation test revealed an insulin-secreting tumor localized in the pancreatic body. She then underwent spleen-preserving distal pancreatectomy; a 10-mm tumor positive for chromogranin A, synaptophysin and insulin was identified.

CONCLUSIONS

Although pregnancy can mask insulinoma-associated symptoms and make diagnosis challenging, hypoglycemic episodes during early pregnancy, which were observed in this case, are suggestive of insulinoma. Importantly, in this case, accurate preoperative localization of the tumor enabled prompt curative surgery after delivery. Thus, clinical vigilance for the occurrence of insulinoma and its localization is appropriate for pregnant women suffering severe hypoglycemia.

Continuous glucose monitoring in a patient with insulinoma presenting with unawareness of postprandial hypoglycemia

Summary

Unawareness of postprandial hypoglycemia for 5 years was identified in a 66-year-old man at a local clinic. The patient was referred to our hospital because of this first awareness of hypoglycemia (i.e. lightheadedness and impaired consciousness) developing after lunch. In a 75 g oral glucose tolerance test, the plasma glucose concentration was decreased to 32 mg/dL (1.8 mmol/L) at 150 min with relatively high concentrations of insulin (8.1 μU/mL), proinsulin (70.3 pmol/L), and C-peptide (4.63 ng/mL). In a prolonged fasting test, the plasma glucose concentration was decreased to 43 mg/dL (2.4 mmol/L) at 66 h with an insulin concentration of 1.4 μU/mL and a C-peptide concentration of 0.49 ng/mL. Computed tomography showed an 18 mm hyperenhancing tumor in the uncinate process of the pancreas. A selective arterial calcium stimulation test showed an elevated serum insulin concentration in the superior mesenteric artery. The patient was then diagnosed with insulinoma and received pancreaticoduodenectomy. Continuous glucose monitoring (CGM) using the Dexcom G6 system showed unawareness of hypoglycemia mainly during the daytime before surgery. When the sensor glucose value was reduced to 55 mg/dL (3.1 mmol/L), the Dexcom G6 system emitted an urgent low glucose alarm to the patient four times for 10 days. Two months after surgery, an overall increase in daily blood glucose concentrations and resolution of hypoglycemia were shown by CGM. We report a case of insulinoma with unawareness of postprandial hypoglycemia in the patient. The Dexcom G6 system was helpful for assessing preoperative hypoglycemia and for evaluating outcomes of treatment by surgery.

Learning points

Insulinoma occasionally leads to postprandial hypoglycemia. The CGM system is useful for revealing the presence of unnoticed hypoglycemia and for evaluating treatment outcomes after surgical resection. The Dexcom G6 system has an urgent low glucose alarm, making it particularly suitable for patients who are unaware of hypoglycemia.

Big insulin-like growth factor 2-producing multiple solitary fibrous tumors treated with debulking surgery: A case report

BACKGROUND

Non-islet cell tumor hypoglycemia (NICTH) is a rare paraneoplastic syndrome caused by a tumor-producing high molecular weight form of insulin-like growth factor 2 (IGF2) known as big IGF2. The only curative treatment for this condition is surgical resection of the responsible tumors. However, this may not be feasible in cases with multiple metastases at diagnosis of NICTH, and no standard treatment strategy for multiple tumors has been established. The effects of pharmacological therapies including somatostatin analogs are often inefficient and remain difficult to predict.

CASE DESCRIPTION

A 68-year-old man was admitted to our hospital due to impaired consciousness and severe hypoglycemia. His medical history included diagnosis of a left temporal solitary fibrous tumor (SFT) at the age of 48 years, after which local recurrent and metastatic tumors were repeatedly resected. Four years before admission, multiple intraabdominal and subcutaneous tumors were detected and, being asymptomatic, were managed conservatively. Laboratory exam on admission demonstrated hypoglycemia accompanied with low serum insulin and IGF1 levels. Computed tomography (CT) scan revealed multiple intraabdominal and subcutaneous tumors increasing in size. Serum big IGF2 was detected on immunoblot analysis, and he was diagnosed as NICTH. In addition, tumor uptake was observed on ⁶⁸Ga-labelled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-d-Phe¹-Tyr³-octreotide positron emission tomography/CT (DOTATOC-PET/CT). Since larger tumor is more suspicious about responsible producibility of big IGF2, we planned to resect large ones preferentially and reduce the amounts of residual tumors. Debulking surgery was performed by removing eleven intraabdominal tumors; the hypoglycemia was then completely corrected. Histological analyses revealed the resected tumors to be metastases of SFT having somatostatin receptor 2 expression. In immunoblot analysis, the resected tumors were found to be positive for big IGF2; serum big IGF2 was undetectable after surgery.

CONCLUSION

We present a case of NICTH with multiple metastatic SFTs. We strategically performed debulking surgery, which led to remission of hypoglycemia. This result demonstrates a pioneering practical solution for NICTH cases with multiple tumors. In addition, in cases of SFTs presenting with NICTH, positivity of DOTATOC-PET/CT as well as single-dose administration of octreotide may be predictive of the efficacy of somatostatin-based therapy.

Review: experimentally induced hypoglycemia-associated autonomic failure in humans: determinants, designs and drawbacks

Context

Iatrogenic hypoglycemia remains one of the leading hindrances of optimal glycemic management in insulin-treated diabetes. Recurring hypoglycemia leads to a condition of hypoglycemia-associated autonomic failure (HAAF). HAAF refers to a combination of (i) impaired hormonal counterregulatory responses and (ii) hypoglycemia unawareness to subsequent hypoglycemia, substantially increasing the risk of severe hypoglycemia. Several studies since the 1990s have experimentally induced HAAF, yielding variable results.

Objective

The aim of this review was to assess the varying designs, clinical outcomes, potential assets, and drawbacks related to these studies.

Method

A systemic literature search was conducted on PubMed and Embase in winter 2021 to include all human studies attempting to experimentally induce HAAF. In different combinations, the search terms used were “hypoglycemia-associated autonomic failure,” “HAAF,” “hypoglycemia,” “recurring,” “recurrent,” “repeated,” “consecutive,” and “unawareness,” yielding 1565 publications. Inclusion criteria were studies that had aimed at experimentally inducing HAAF and measuring outcomes of hormonal counterregulation and awareness of hypoglycemia.

Results

The literature search yielded 27 eligible publications, of which 20 were successful in inducing HAAF while statistical significantly impairing both hormonal counterregulation and impairing awareness of hypoglycemia to subsequent hypoglycemia. Several factors were of significance as regards inducing HAAF: Foremost, the duration of antecedent hypoglycemia should be at least 90 minutes and blood glucose should be maintained below 3.4 mmol/L. Other important factors to consider are the type of participants, insulin dosage, and the risk of unintended hypoglycemia prior to the study.

Conclusion

Here we have outlined the most important factors to take into consideration when designing a study aimed at inducing HAAF, including to take into consideration other disease states susceptible to hypoglycemia, thus hopefully clarifying the field and allowing qualified studies in the future.

Lanreotide and diazoxide have comparable effects on glucose levels in an elderly Japanese insulinoma patient: a case report

An insulinoma is a pancreatic neuroendocrine tumor that causes hypoglycemia. In the elderly, as surgery is not always possible, drugs are an important alternative. However, the effects of lanreotide on insulinomas have not yet been elucidated. We report the case of an 85-year-old Japanese woman who was admitted for loss of consciousness and hypoglycemia, which was resolved after intravenous glucose infusion. Insulin secretion was not inhibited during hypoglycemia. Enhanced computed tomography and OctreoScan scintigraphy revealed a pancreatic tumor (diameter, 13 mm) with radiotracer accumulation. Thus, clinical insulinoma was confirmed. However, the patient refused further examination and surgery. Diazoxide (150 mg/day) therapy resolved hypoglycemia but caused fluid retention. Consequently, we switched to lanreotide (120 mg/6 weeks). Continuous glucose monitoring revealed that both drugs had comparable effects on interstitial glucose normalization. Furthermore, 447 days after the initiation of lanreotide treatment, the patient had no hypoglycemic symptoms. Therefore, lanreotide may be a useful alternative treatment option for inoperable insulinomas in elderly individuals.

Insulinoma presenting with postprandial hypoglycemia and a low body mass index: A case report

BACKGROUND

Insulinomas are the most common type of functioning endocrine neoplasms of the pancreas presenting hypoglycemic symptoms. Patients characteristically develop symptoms while fasting, but some patients have reported symptoms only in the postprandial state. Repeated and prolonged hypoglycemic episodes can reduce the awareness of adrenergic symptoms, and patients may have amnesia, which delays diagnosis.

CASE SUMMARY

We describe a case of a 24-year-old underweight patient who showed hypoglycemic symptoms for almost 6 years. Although patients with insulinoma characteristically develop symptoms while fasting, this young man had hypoglycemic symptoms up to one hour postprandially, especially after high-sugar meals and after physical activity. The fasting tests and imaging methods performed at local hospitals were evaluated as negative for abnormal results. However, brown adipose tissue exhibited increased metabolic activity, and some muscle groups had histological changes as indicated by positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography. Glycogen deficiency was also histologically confirmed. The patient’s symptoms progressed over the years and occurred more frequently, i.e., several times a month, and the patient had reduced awareness of adrenergic symptoms. The follow-up fasting test was positive, and the imaging results showed a tumor in the head of the pancreas. The patient underwent laparotomy with enucleation of the insulinoma.

CONCLUSION

Weight gain and fasting hypoglycemia are not necessarily characteristics of insulinoma. In prolonged cases, adrenergic symptoms can be suppressed.

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

Background

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.

Case presentation

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.

Conclusions

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.

Factory-calibrated continuous glucose monitoring and capillary blood glucose monitoring in a case with insulinoma: usefulness and possible pitfall under chronic hyperinsulinemic hypoglycemia

The accuracy of factory-calibrated continuous glucose monitoring (fCGM) within hypoglycemic ranges, especially under the status of chronic hyperinsulinemic hypoglycemia like insulinomas, remains an issue. Even so, fCGM is known to be useful for detecting hypoglycemia unawareness in insulinoma cases. A 25-year-old woman presenting with sudden unconsciousness was diagnosed with insulinoma; fCGM facilitated diagnosis by continuous monitoring for hypoglycemia. Before surgery, she was treated with continuous and frequent bolus infusions of 50% glucose via central venous catheter. To evaluate the accuracy of fCGM values in this case, a comparison between fCGM and capillary blood glucose (CBG) values was also performed. According to the simultaneously measured values, those of fCGM were largely in accordance with those of CBG. Moreover, compared with the previously reported case not having glucose infusions via central venous catheter, both the mean absolute relative differences (MARDs) and the absolute differences (Δ glucose) between fCGM and CBG values were larger in the present case, although no significant differences of MARDs and Δ glucose between the two cases were observed in several different conditions including fasting, post-meal, hypoglycemia, and others. Therefore, we should note possible increased differences between fCGM and CBG values in cases using frequent intravenous glucose infusions as well as case-dependent differing levels of consistency between them.

USE OF A CONTINUOUS GLUCOSE MONITOR FOR PREOPERATIVE MONITORING AND TREATMENT OF HYPOGLYCEMIA IN A CASE OF PANCREATIC NEUROENDOCRINE TUMOR

Objective

Pancreatic neuroendocrine tumors secreting proinsulin and insulin could lead to life-threatening hypoglycemia. We aim to show this can be avoided by utilizing continuous glucose monitoring.

Methods

We describe a case of a 55-year-old female with hypoglycemia unawareness and seizures diagnosed with proinsulinoma. She utilized an intermittently scanned continuous glucose monitor (isCGM) to monitor hypoglycemia preoperatively.

Results

The patient underwent biochemical and radiographic evaluation to confirm the diagnosis of proinsulinoma. Utilizing isCGM to monitor blood glucose, she was able to prevent hypoglycemia-related seizures prior to definitive surgery.

Conclusion

In the time leading up to a definitive surgery, patients with proinsulinomas are at risk of hypoglycemic events leading to falls, seizures, and even death. isCGMs can be utilized for preoperative monitoring and treatment of hypoglycemia in these patients.