Snapshot A 42-year-old man presents to the clinic with complaint of watery diarrhea for the past four months. He states that he has not seen any blood in his stool. Upon further questioning, he states that he has also experienced intermittent abdominal pain and asthma attacks. On physical examination, the patient's face and neck appears as seen in the image. Introduction Overview carcinoid syndrome is a rare syndrome that is caused by the metastasis of carcinoid tumors that secrete high levels of serotonin (5-HT) treatment is usually with surgical resection or octreotide Epidemiology Incidence rare, 1-2 cases per 100,000 individuals Demographics most frequently in patients 50-70 years ETIOLOGY Pathophysiology metastasis of carcinoid tumors that produce serotonin carcinoid tumors most commonly located in the ileum and appendix (90%) carcinoid tumors arise from neuroendocrine cells carcinoid syndrome is observed if there is metastasis of the tumor outside of the GI system if there is metastasis to the liver, first-pass metabolism of secreted serotonin is disrupted and hormones reach systemic circulation Associated conditions medical conditions pellagra caused by niacin (vitamin B3) deficiency all tryptophan is consumed in making excess 5-HT Presentation Symptoms common symptoms cutaneous flushing recurrent diarrhea ↑ bowel motility abdominal cramps asthma-like wheezing Physical exam erythema pellagra skin lesions wheezing hepatomegaly from metastases pulmonary systolic and diastolic heart murmur cardiac involvement causes carcinoid heart disease primarily occurs on right side of the heart tricuspid valve most commonly affected Imaging CT indication localize the primary tumor assess extent of tumor spread and metastases In-111 octreotide scan indication localize the primary carcinoid tumor and recurrences Studies Labs measurement of urinary excretion of 5-HIAA best initial test urinary excretion of 5-HIAA ≥ 25mg/day is diagnostic 5-HT is degraded to 5-HIAA and excreted in the urine Differential VIPoma key distinguishing factor presents with WDHA syndrome Watery Diarrhea Hypokalemia Achlorhydria may present with flushing similar to carcinoid syndrome but no wheezing or right-sided heart murmurs are present Treatment Surgical surgical resection of tumor indications first-line treatment reduces tumor mass and achieves symptom remission Medical octreotide or other somatostatin analog indications alleviates flushing and diarrhea Complications Carcinoid heart disease incidence up to 50% of patients with carcinoid syndrome risk factors higher urinary levels of 5-HIAA associated with greater risk of progression of carcinoid heart disease treatment somatostatin analogs