What is carcinoid syndrome?

What is carcinoid syndrome?

Tumors of the small intestine, principally the ileum, which have metastasized to the liver, produce the syndrome. Carcinoid tumors in the liver present direct access of vasoac-tive substances to the circulation. The hormones secreted by primary gastrointestinal carcinoid tumors reach the liver by way of the portal vein where they are usually inactivated. Once metastases to the liver have occurred, hormones secreted by hepatic involvement have direct access to the sys-temic circulation, thus producing the signs and symptoms of the carcinoid syndrome. Serotonin, which is the most com-mon substance producing carcinoid syndrome, can cause changes in the skin, gastrointestinal tract, respiratory tract, and heart. The most frequent clinical feature is cutaneous flushing. The typical flush is erythematous and involves the head and neck. The color may change from red to violet. Prolonged flushing may be associated with lacrimation and periorbital edema. This is the phenomenon known as the vasomotor paroxysmal syndrome.

Many patients with carcinoid tumors do not exhibit generalized symptoms of the syndrome. Only about 8% of patients with carcinoid tumors actually display the carci-noid syndrome itself. Seventy-five percent of these patients have cutaneous flushing, 67% have intestinal hypermotility leading to dehydration and metabolic acidosis. Forty-one percent have cardiac involvement, usually on the right side of the heart, most commonly the tricuspid or pulmonic valves. This is thought to be due to chronic serotonin stimulation of the endocardium. Tricuspid insufficiency is more common than pulmonic stenosis. The left-sided heart valves are usually spared, possibly due to pulmonary parenchymal cells, which inactivate vasoactive substances. Only 18% of patients with carcinoid syndrome present with wheezing. This is seen more frequently with gastric tumors. Some patients with carcinoid tumors may present with iron deficiency anemia from gastrointestinal bleeding or vitamin B₁₂ and folic acid deficiencies. Clotting disorders can also occur caused by malabsorption of the fat-soluble vitamins. In rare cases, pellagra can occur from niacin deficiency.