The most common GI endocrine neoplasm is carcinoid syndrome, which produces vasoactive products, including 5-hydroxytryptophan, serotonin, bradykinin, and histamine. Symptoms of carcinoid syndrome include vasomotor flushing, episodic hypotension, and diarrhea. Diagnosis requires demonstrating elevation of tumor products or metabolites, such as increased urinary 5-hydroxyindoleacetic acid excretion. Uncontrolled gastric acid secretion causes severe peptic ulcer disease. Diarrhea resulting from mucosal damage in the small intestine and denaturation of pancreatic enzymes occurs in approximately half of patients.
Diagnosis rests on detection of elevated fasting levels of serum gastrin.
Diarrhea responds to acid antisecretory therapy. Patients typically have voluminous watery diarrhea. Other uncommon causes of secretory diarrhea include medullary carcinoma of the thyroid and glucagonoma, a glucagon-secreting tumor of the pancreas that causes weight loss, anemia, hyperglycemia, and a scaling erythematous dermatitis.