A 50-year-old man with flushing, secretory diarrhoea, and elevated urinary 5-HIAA develops a new pansystolic murmur at the left lower sternal edge increasing with inspiration. Echocardiography shows thickened, fixed, retracted tricuspid and pulmonary valve leaflets with restricted motion. Which statement best explains the pattern of valvular involvement?

• A The lesions result from recurrent microemboli from hepatic metastases
• B Left-sided valves are involved first because they face higher pressures
• C The valvular damage is caused by circulating immune complexes
• D Serotonin is degraded by pulmonary monoamine oxidase, protecting the left-sided valves ✓

Explanation

In carcinoid heart disease, vasoactive substances such as serotonin released by hepatic metastases reach the right heart directly and cause fibrous endocardial plaques on right-sided valves. Pulmonary monoamine oxidase inactivates these mediators, so left-sided valves are spared unless there is a patent foramen ovale or primary bronchial carcinoid with pulmonary metastases. Immune complexes and microemboli are not implicated.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.