Question

Differential cyanosis (pink upper limbs with cyanosed lower limbs) is characteristically seen in:

• A. Patent ductus arteriosus (PDA) with reversal of shunt / Eisenmenger
• B. Osler-Weber-Rendu syndrome
• C. Peripheral arterial disease
• D. Transposition of great arteries (simple)

Hint:

Blue legs, pink arms means desaturated blood enters the aorta distal to the subclavian via a duct.

Answer 1

The Correct Option is A

Step 1: Define differential cyanosis. Differential cyanosis means the lower limbs are cyanosed (and clubbed) while the upper limbs / head remain pink. It indicates that deoxygenated blood is reaching the descending aorta while the upper body still receives oxygenated blood.

Step 2: Identify the lesion. This occurs in a large PDA with pulmonary hypertension and reversal of the shunt (Eisenmenger physiology). Desaturated blood from the pulmonary artery crosses the duct into the descending aorta (distal to the left subclavian), supplying the lower body, while the head and right arm get pre-ductal oxygenated blood.

Step 3: Why the others are wrong. Osler-Weber-Rendu (hereditary haemorrhagic telangiectasia) causes mucocutaneous telangiectasias and AVMs, not a regional cyanosis gradient. Peripheral arterial disease gives limb ischaemia/acrocyanosis, not the classic upper-pink/lower-blue pattern of a cardiac shunt. Simple TGA causes reversed differential cyanosis only in special combinations.

Key fact: Differential cyanosis (pink arms, blue legs) = PDA with right-to-left shunt / Eisenmenger syndrome.