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.