Uniform central cyanosis is cyanosis of both upper and lower limbs along with cyanosis of lips and tongue. In differential cyanosis, there is cyanosis of lower limbs without cyanosis of upper limbs. This occurs typically in patent ductus arteriosus with reversal of shunt due to severe pulmonary hypertension. In a neonate differential cyanosis can occur due to persistent pulmonary hypertension, aortic arch hypoplasia, interrupted aortic arch, critical coarctation, and critical aortic stenosis with patent ductus arteriosus . Reverse differential cyanosis with cyanosis of upper limbs and no cyanosis of lower limbs occurs in more complex congenital heart diseases.
Reverse differential cyanosis can occur in complete transposition of great arteries or Taussig-Bing anomaly with reversal of ductal flow due to severe pulmonary hypertension. Taussig Bing anomaly is double outlet right ventricle with subpulmonic ventricular septal defect along with transposition of the aorta to the right ventricle and malposition of the pulmonary artery. Reversal of ductal flow can also occur if there is a pre-ductal coarctation or interruption of aortic arch as the descending aortic pressure is low and below that of the pulmonary artery. In all these situations saturated blood from the left ventricle is pumped into the pulmonary artery and into the descending aorta across the patent ductus arteriosus. Desaturated right ventricular blood is pumped into the aorta and reaches the upper limbs, head and neck [2,3].
Another very rare situation in which reverse differential cyanosis has been reported is a supracardiac total anomalous pulmonary venous connection with streaming of highly saturated superior vena caval blood into the right ventricle. It was pumped into the pulmonary artery and across a patent ductus arteriosus into the descending aorta in a neonate. Desaturated inferior vena caval blood was streaming to the left atrium across the atrial septal defect. Hence desaturated blood reached the upper limbs through the left ventricle and aorta, producing reverse differential cyanosis .
Critical aortic stenosis and hypoplastic aortic arch can cause reversed flow from pulmonary artery through a patent ductus arteriosus into the descending aorta. Some such cases may have pink acyanotic right arm with cyanosis of left arm and legs . This is because left subclavian is in the low pressure zone beyond the aortic obstruction. Hence it is usual to check saturation in the right upper limb rather than the left upper limb along with lower limbs while assessing differential cyanosis. A better way would be to check oxygen saturation in all four limbs in the neonate.
Reverse differential cyanosis in a newborn has been considered as a treatable cardiac emergency . Initial management is with oxygen and prostaglandin E1 infusion to maintain ductal patency. Atrial septostomy is useful in enhancing the mixing at the atrial level and thereby improving systemic oxygen saturation. Pulmonary hypertension can be relieved by nitric oxide inhalation and bosentan. Some of the very sick neonates may need extracorporeal membrane oxygenation (ECMO) support. These neonates are taken up for arterial switch operation soon after stabilization. Repair of other associated defects are also needed.
Singh J, Singh A. Differential cyanosis. Am J Med. 2013 Oct;126(10):e9. doi: 10.1016/j.amjmed.2013.03.014. PMID: 24054964.