Proinsulin Expressing Neuroendocrine Tumors of the Pancreas: An Underrecognized Entity

Investigation and Causes of Spontaneous (Non-Diabetic) Hypoglycaemia in Adults: Pitfalls to Avoid

Although adult spontaneous (non-diabetic) hypoglycaemia is rare, its recognition is important for the preventative or curative treatment of the underlying cause. Establishing Whipple's triad-low blood glucose, neuroglycopaenia and resolution of neuroglycopaenia on increasing blood glucose levels to normal or above-is essential to verify hypoglycaemia. Awareness that hypoglycaemia may occur in severely ill patients is important for its prevention. Further investigation in such cases is unnecessary unless another cause of hypoglycaemia is suspected. Patients are often asymptomatic and normoglycaemic at review. Their history of medication, self-medication, access to hypoglycaemic drugs, alcohol use and comorbidity may provide aetiological clues. The investigation involves obtaining blood samples during symptoms for laboratory glucose measurement or provoking fasting or postprandial hypoglycaemia as directed by symptoms. If confirmed, insulin, c-peptide, proinsulin and beta-hydroxybutyrate are analysed in hypoglycaemic samples. These will classify hypoglycaemia due to non-ketotic hyperinsulinaemia, non-ketotic hypoinsulinaemia and ketotic hypoinsulinaemia, and direct investigations to identify the underlying cause. There are, however, many pitfalls that may mislabel healthy individuals as "hypoglycaemic" or misdiagnose treatable or preventable causes of spontaneous hypoglycaemia. Clinical acumen and appropriate investigations will mostly identify hypoglycaemia and its cause.

A Novel Somatic Mutation Implicates ATP6V0D1 in Proinsulin Processing

Context

Prohormone convertase 1/3 (PC1/3), encoded by protein convertase subtilisin kexin type 1 (PCSK1), converts inactive prohormones into biologically active peptides. Somatic mutations of insulinomas are associated with genetic defects interfering with control of insulin secretion from pancreatic beta cells. However, somatic mutations in proinsulinomas have not been described.

Objective

We report a case of a proinsulinoma, with suppressed insulin and C-peptide levels.

Methods

A 70-year-old woman presented with a 20-year history of "blackouts." During a 72-hour fast, blood glucose level dropped to 1.9 mmol/L with suppressed plasma insulin and C-peptide levels, but proinsulin levels were raised at 37 pmol/L (<10 pmol/L).

Results

Imaging revealed 3 distinct DOTATATE-avid pancreatic lesions. Laparoscopic spleen-preserving distal pancreatomy was performed. In view of discordant insulin, C-peptide, and proinsulin levels, whole exome sequencing analysis was performed on the tumor. In the somatic exome of the tumor, we found mutations in PCSK expression regulators, as well as a novel truncating somatic mutation in ATP6V0D1, a subunit of the ion pump that acidifies the β-cell compartments where the PCSKs act.

Conclusion

Appropriately suppressed insulin levels in the context of hypoglycemia do not always indicate the absence of a neuroendocrine islet cell tumor and proinsulin levels may be indicated to solidify the diagnosis. In the context of elevated proinsulin levels, low insulin and C-peptide levels might be explained by somatic mutations that likely implicate proinsulin processing within the tumor. Furthermore, we propose several mechanistic candidates, including ATP6V0D1. Experimental validation using cellular approaches may in future confirm pathomechanisms involved in this rare condition.

Adult Proinsulinomatosis Associated With a MAFA Germline Mutation as a Rare Cause of Recurrent Hypoglycemia

Sporadic adult insulinomatosis is an extremely rare clinical condition. Adult proinsulinomatosis has not yet been described. We report the case of a 48-year-old female patient with recurrent hypoglycemia caused by benign proinsulin-secreting pancreatic neuroendocrine neoplasias (pNENs) with no history of multiple endocrine neoplasia type 1. Initial workup revealed elevated serum proinsulin levels and a positive fasting test. Magnetic resonance imaging and endosonography visualized 2 pNENs in the pancreatic body and tail that were treated by robotic-assisted enucleation. After initial biochemical cure, the patient's hypoglycemia recurred 3 months after surgery. Imaging showed a new lesion in the pancreatic body, so that now a spleen-preserving subtotal distal pancreatectomy was performed. The pathological examination revealed 17 neuroendocrine microadenomas and 1 well-differentiated pNEN (Ki-67% 1%-2%) of 22-mm size as well as more than 200 (pro)insulin-producing β-cell precursor lesions, confirming the diagnosis of adult proinsulinomatosis. Mutation analysis of the germline DNA identified the in-frame deletion mutation (p.His207del) in the MAFA gene on chromosome 8. The patient was biochemically cured 16 months after the last surgical resection. Similarly to adult insulinomatosis, the presence of proinsulin-secreting tumors causes recurrent hypoglycemia and might be associated with germline mutations in the MAFA gene.

[Pancreatic proinsulinoma]

OBJECTIVE

To report own experience in the treatment of patients with proinsulinoma.

MATERIAL AND METHODS

There were 10 patients with increased proinsulin production and normal insulin level since 2017. Most of them were young women.

RESULTS

Fasting hypoglycemia in all patients was severe (up to 0.7 mmol/l). Clinical picture consisted of typical symptoms similar to those in insulinoma. The main difference in the course of proinsulinoma was the absence of weight gain in 7 patients and rapid weight loss (from 210 to 90 kg within 9 months) in 1 patient. All patients with proinsulinoma underwent surgery. In most cases, minimally aggressive surgery was performed.

CONCLUSION

Proinsulinoma is an extremely rare endocrine-active neuroendocrine pancreatic tumor. Differential features of proinsulinoma are the absence of weight gain and normal insulin levels in the presence of hypoglycemia. Surgery is the only radical method of treatment.

The functioning side of the pancreas: a review on insulinomas

PURPOSE

Insulinomas are a rare type of neuroendocrine tumors, originating in the pancreas, difficult to diagnose and to treat. Due to its rarity, insulinomas are a not well-known pathological entity; thus, the diagnostic process is frequently a medical challenge with many possible differential diagnoses. The diagnostic process varies between non-invasive procedures, such as the fasting test or imaging techniques, and invasive ones. Insulinomas are rarely malignant, but the glycemic imbalance correlated with this tumor can frequently alter the quality of life of the patients and the consequent hypoglycemia can be extremely dangerous. Moreover, insulinomas can be associated with different genetic syndromes, such as Multiple Endocrine Neoplasia 1, accompanied by other specific symptoms. There are many different treatment strategies, depending on the need to control symptoms or control diseases progression, the only curative one being surgery.

METHODS AND RESULTS

We reviewed the evidences present in the literature on insulinomas and reported its main clinical characteristics and management strategies.

CONCLUSION

The aim of this review of the literature is to present the current knowledge on insulinomas, exploring the main clinical characteristics, the diagnostic tools, and the therapeutic strategies.

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.

Hypoglycemia After Upper Gastrointestinal Surgery: Clinical Approach to Assessment, Diagnosis, and Treatment

CONTEXT

Post-bariatric hypoglycemia (PBH) is an increasingly encountered complication of upper gastrointestinal surgery; the prevalence of this condition is anticipated to rise given yearly increases in bariatric surgical procedures. While PBH is incompletely understood, there is a growing body of research describing the associated factors, mechanisms, and treatment approaches for this condition.

EVIDENCE ACQUISITION

Data are integrated and summarized from studies of individuals affected by PBH and hypoglycemia following upper gastrointestinal surgery obtained from PubMed searches (1990-2020).

EVIDENCE SYNTHESIS

Information addressing etiology, incidence/prevalence, clinical characteristics, assessment, and treatment were reviewed and synthesized for the practicing physician. Literature reports were supplemented by clinical experience as indicated, when published data were not available.

CONCLUSION

PBH can be life-altering and severe for a subset of individuals. Given the chronic nature of this condition, and sequelae of both acute and recurrent episodes, increasing provider awareness of both the condition and associated risk factors is critical for assessment, prompt diagnosis, treatment, and preoperative identification of individuals at risk.

Proinsulin-Secreting Neuroendocrine Tumors of the Pancreas: A Single-Centre Experience

Background

Proinsulinoma is a neuroendocrine tumor (NET) of the pancreas that produces prohormone proinsulin. These tumors are very rare. In the literature, they are most often presented in the form of case reports.

Materials and Methods

We studied 177 patients with NET of the pancreas who underwent surgical treatment in the A.V. Vishnevsky National Medical Research Centre of Surgery from January 2007 to December 2018.

Results

Of 81 patients with organic hyperinsulinism caused by functioning NETs of the pancreas during the study period, 3 (3.7%) had a proinsulinoma; 2 were female; and 1 was male. None of them admitted to weight gain during this period, and their BMI was normal. All patients presented with Whipple's triad during the 72-h fast. Tumor-enucleating surgery was performed: one robot assisted, two laparotomies. A normal glucose level after treatment was achieved in all cases.

Conclusion

In cases where clinical hypoglycemia is present, but the serum insulin level is within the normal range or even decreased, proinsulinoma should be suspected. For now, surgical resection remains the only effective method of treatment. Further investigation of pro-insulinomas is needed.