This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Acyanotic congenital hea diseases, Subject name: Pediatrics
[{'content': 'A 4 year old child had cyanosis only involving the lower limbs, but not involving the upper limbs. Which of the following could be a possible underlying cause for differential cyanosis? \nSelect and explain. \nA. PDA with reversal of shunt, B. VSD with Eissenmenger syndrome, C. Tetralogy of Fallot, D. ASD with reversal of shunt', 'role': 'user'}, {'content': 'Answer: A \nExplanation: --> Differential cyanosis is seen in PDA with reversal of shunt --> Differential cyanosis: No cyanosis in upper limbs --> as oxygenated blood goes there. Cyanosis in lower limbs --> d/t mixing of oxygenated blood with deoxygenated blood. PATENT DUCTUS AERIOSUS : --> Failure of closure of Ductus aeriosus after bih , resulting in persistent connection b/w aoa & pulmonary aery. --> Hypoxia & prematurity predispose to PDA --> AUSCULTATION --> Continuous machinery murmur is seen --> DOC for medical closure of PDA in preterm neonate --> PG Inhibitor --> Normally PDA is acyanotic hea disease but with reversal of shunt, differential cyanosis is seen.', 'role': 'assistant'}]