Hypoglycemic Syndrome without Hyperinsulinemia. A Diagnostic Challenge.

Area of Science:

• Endocrinology
• Oncology
• Gastroenterology

Background:

• Organic fasting hypoglycemia in adults is often caused by insulin-producing pancreatic adenomas.
• When insulin levels are not elevated, diagnosing insulinoma is challenging and can lead to misdiagnosis, such as unnecessary pancreatectomy.
• Proinsulinoma, a rare condition, should be considered when insulin levels are suppressed despite symptoms of insulinoma.

Purpose of the Study:

• To describe an unusual case of proinsulinoma presenting as severe fasting hypoglycemia.
• To highlight the diagnostic challenges and workup required for rare proinsulin-secreting pancreatic adenomas.
• To confirm the diagnosis through clinical, biochemical, and histopathological findings.

Main Methods:

• Case report of a 38-year-old man with severe hypoglycemic syndrome.
• Measurement of serum insulin, proinsulin, and C-peptide levels during fasting hypoglycemia.
• Identification of an islet cell tumor via further tests and subsequent surgical removal.
• Histopathological examination of the tumor with specific immunostaining for proinsulin and insulin.

Main Results:

• The patient presented with severe hypoglycemia, but insulin levels were suppressed.
• Serum proinsulin and C-peptide levels were significantly elevated, indicating proinsulinoma.
• Histopathology revealed a neuroendocrine tumor with high proinsulin and lower insulin immunoreactivity.
• Surgical removal of the tumor resolved the hypoglycemia and normalized proinsulin levels.

Conclusions:

• Proinsulinoma is a rare but important cause of organic fasting hypoglycemia that can be misdiagnosed.
• Elevated proinsulin and C-peptide levels are key biochemical markers for diagnosing proinsulinoma.
• Accurate diagnosis and surgical resection of proinsulinomas lead to complete symptom resolution.