The differential diagnosis of flushing includes physiologic, drug-related, and neoplastic etiologies, but carcinoid syndrome should be suspected when flushing occurs with diarrhea and dyspnea. Carcinoid syndrome results from the systemic release of serotonin and other vasoactive substances by well-differentiated neuroendocrine tumors. Diagnosis is made by elevated 24-hour urinary 5-hydroxyindoleacetic acid, a serotonin metabolite. As tryptophan-/serotonin-rich foods can cause false-positive results, patients should avoid such foods for 24–72 hours prior to testing. Treatment typically involves long-acting somatostatin analogs, which can be dosed more frequently for refractory symptoms.
Comment
The differential diagnosis of flushing includes physiologic, drug-related, and neoplastic etiologies, but carcinoid syndrome should be suspected when flushing occurs with diarrhea and dyspnea. Carcinoid syndrome results from the systemic release of serotonin and other vasoactive substances by well-differentiated neuroendocrine tumors. Diagnosis is made by elevated 24-hour urinary 5-hydroxyindoleacetic acid, a serotonin metabolite. As tryptophan-/serotonin-rich foods can cause false-positive results, patients should avoid such foods for 24–72 hours prior to testing. Treatment typically involves long-acting somatostatin analogs, which can be dosed more frequently for refractory symptoms.