# Normalization of Prediabetic Hemoglobin A1c (HbA1c) Levels After the Surgical Removal of a Serotonin-Secreting Neuroendocrine Tumor

## TL;DR

A patient's prediabetic blood sugar levels returned to normal after surgery to remove a serotonin-producing tumor, suggesting such tumors may affect glucose metabolism.

## Contribution

This case highlights impaired glucose tolerance as a potential early sign of serotonin-secreting neuroendocrine tumors.

## Key findings

- Prediabetic HbA1c levels normalized after surgical removal of a serotonin-secreting NET.
- The patient had intractable diarrhea but no other signs of carcinoid syndrome before surgery.
- Impaired glucose tolerance may be an early indicator of serotonin-secreting NETs.

## Abstract

Neuroendocrine tumors (NETs) are rare. When present, they often produce serotonin and are called carcinoids. Serotonin-secreting NETs can present with or without carcinoid syndrome. Although the idea of serotonin-secreting NETs potentially altering glucose metabolism is not new, data around this issue has been scarce, with only a few limited studies and case reports. We present a case where a female patient’s prediabetic hemoglobin A1C levels normalized after removing serotonin-secreting NET. Before removal, the patient had locally metastatic carcinoid and serotonin-related intractable diarrhea but did not exhibit any other sign of carcinoid syndrome, including flushing, which is considered a hallmark. Therefore, in suggestive clinical contexts, this case points to the possibility of impaired glucose tolerance being an early clinical sign of carcinoid that could aid in serotonin-secreting NET diagnosis before it manifests as overt carcinoid syndrome.