Diarrhea as an Initial Presentation in Patients with Medullary Thyroid Cancer: Delaying the Diagnosis.

Tumoral secretion of various molecular factors, such as calcitonin (Ct), can cause diarrhea in patients with medullary thyroid cancer (MTC). We report 3 patients (age 26-38 years, serum Ct levels ranging from 2,890 to 52,894 ng/L) with chronic diarrhea, and the diagnosis of MTC was delayed. Diarrheal symptoms improved after thyroid surgery. Two patients with elevated Ct had no diarrhea. The link between tumor humoral secretion and diarrhea is not well established in patients with MTC. Diarrhea is more common in patients with metastatic disease and improves after resection of the tumor. Diarrhea may result from elevated circulating levels of Ct or other substances, such as prostaglandins or serotonin. Other proposed mechanisms include decreased absorption in the colon secondary to gastrointestinal motor disturbances. In conclusion, MTC should be considered when evaluating chronic diarrhea.