Carcinoid syndrome

The carcinoid syndrome occurs in approximately 10% of all neuroendocrine tumors This may be heard as a murmur and may contribute to fatigue. Less common symptoms include malabsorption (leading to pellagra), fatigue, muscle loss, and cognitive impairment. Late complications may include mesenteric and retroperitoneal fibroses as well. == Pathophysiology ==

The carcinoid syndrome occurs secondary to neuroendocrine tumors. Neuroendocrine tumors produce several biologically active substances, mainly amines and peptides. Increased amounts of serotonin lead to increased gut motility causing the diarrhea seen in carcinoid syndrome. Carcinoid heart disease Carcinoid heart disease is the result of valvular damage related to the vasoactive substances released by the neuroendocrine tumor reaching the right side of the heart. This mainly affects the right side of the heart unless there is anomalous circulation (i.e. patent foramen ovale) because the lungs will metabolize the substances released by the tumor similar to how the liver will. After initial tissue injury around the valves, plaque will develop and fibrosis will occur, possibly mediated by excess serotonin. == Diagnosis ==

With a certain degree of clinical suspicion, the most useful initial test is the 24-hour urine levels of 5-HIAA (5-hydroxyindoleacetic acid), the end product of serotonin metabolism. Chromogramin A, a glycoprotein released by neuroendocrine tumors, can be used to detect non-secreting tumors. Imaging Imaging studies should be largely focused on the abdomen and pelvis because the neuroendocrine tumors causing the carcinoid syndrome largely arise in the gut. Nuclear medicine gamma camera imaging that utilizes radioactive somatostatin analogues such as indium-111 pentetreotide are used to localize the tumor. PET scan can also be used to find the primary tumor site. Bronchoscopy with biopsy can performed if there is evidence of a pulmonary tumor. For patients with serotonin elevated 5x the upper limit of normal or more, an echocardiogram is recommended for evaluation of carcinoid heart disease. Differential diagnosis Other conditions similar to the carcinoid syndrome that should be considered include: • Irritable bowel syndrome • Celiac disease • Ogilvie syndrome == Treatment ==

Treatment of the carcinoid syndrome is focused on controlling the proliferation of the primary tumor and symptomatic control of the symptoms with somatostatin analogues octreotide or lanreotide. These analogues can help control the growth of the tumor itself and the associated symptoms of the carcinoid syndrome. == Epidemiology ==

The incidence of neuroendocrine tumors in the US lies somewhere from 2.7 to 4.3 per 100,000 people, and appears to be increasing over time. The incidence of the carcinoid syndrome is about 0.27 per 100,000 people in the US, about 10% of all people with neuroendocrine tumors. There does not appear to be any variance by gender, although patients of African-American ethnicity appear to be affected by the carcinoid syndrome more often. == Nonhuman animals ==

The carcinoid syndrome can affect other animals similarly to humans. Similarly to humans, the carcinoid syndrome is due to neuroendocrine tumors that arise mainly from the bowel but also from other organs. Common signs in animals include vomiting, diarrhea, and weight loss but other symptoms that are more common in humans such as flushing, hypotension and diarrhea can also occur. Similar to humans, the cause of the carcinoid syndrome is the release of bioactive substances such as serotonin and histamine. == See also ==