Carcinoid syndrome

Carcinoid syndrome is a paraneoplastic syndrome. 

 

Pathophysiology

The syndrome is caused by the secretion of substances from a carcinoid tumour. The primary mediators are serotonin (a neurotransmitter) and kallikrein (an enzyme). Kallikrein catalyses conversion of kininogen to lysyl-bradykinin. This becomes bradykinin, a potent vasodilator.

There are elevated plasma histamine levels, but the mechanism through which this occurs is unclear. 

• Serotonin disturbs GI motility.
• Bradykinin causes facial vasodilation and flushing.
• Histamine causes bronchoconstriction.
• Serotonin promotes cardiac fibrosis, particularly at the tricuspid and pulmonary valves. 

 

Symptoms

• Facial flushing (due to vasodilation of superficial vessels in the skin)
• GI disturbances, especially diarrhoea, nausea, vomiting
• Abdominal pain, cramps
• Wheezing (due to narrowed bronchi)

 

Complications

• Carcinoid heart disease

 

Investigation findings

• Fibrosis of the valvular endocardium
• Secondary restrictive cardiomyopathy