USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which cardiac anomaly is associated with cyanosis and clubbing, particularly in the lower extremities?

1. Coarctation of the aorta

2. Patent ductus arteriosus

3. Aortic stenosis

4. Mitral stenosis

The correct answer is: Patent ductus arteriosus

The correct choice is associated with the presence of cyanosis and clubbing, particularly in the lower extremities. In this context, patent ductus arteriosus leads to increased blood flow to the lungs, resulting in pulmonary over-circulation. However, in certain cases (especially in larger defects or when associated with other conditions, such as Eisenmenger syndrome), the right-to-left shunting can occur, allowing deoxygenated blood to enter the systemic circulation. This can lead to cyanosis, especially noticeable in the extremities, including the lower half of the body. In some children with significant left-to-right shunting, a complication may arise where the shunting reverses direction due to increased pulmonary vascular resistance. This choice highlights a key cardiac anomaly that, under certain circumstances, can lead to the clinical findings of cyanosis and clubbing, particularly affecting the lower extremities. Other conditions listed may not typically present with this specific symptomatology, emphasizing the unique link between patent ductus arteriosus, cyanosis, and clubbing in specific clinical scenarios.