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Case Reports Indian Pediatrics 2001; 38: 1039-1041 |
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Surfactant Protein B Deficieny: A Rare but Lethal Condition in Newborn |
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Saugata Acharyya, Kakoli Acharyya*
Surfactant Protein B deficiency is a rare but lethal disorder affecting relatively mature newborns. It is an autosomal recessive disorder. Hence it is particularly important to diagnose this for its implications in future pregnancies(1). Case Report A female neonate was born at 35 weeks gestation by spontaneous vaginal delivery at a district general hospital. Apgars were 4 at 1 minute and 8 at 5 minutes. The baby needed bag and mask resuscitation at birth and was subsequently sent to post-natal ward. This was the second baby of consanguineous Asian parents and the first baby died in early neonatal period in Pakistan. The cause of death was unknown and this pregnancy was booked at 32 weeks, hence no antenatal screening was possible. Mother did not receive any antenatal steroid. At 6 hours age while the baby was in post-natal ward, she developed a dusky discolora-tion around her mouth and was immediately brought over to special care baby unit. The baby needed head box oxygen and the requirement of oxygen progressively went up. In order to maintain adequate oxygenation it was decided to put her on conventional ventilation under sedation. According to unit protocol the baby was given a single dose of artificial surfactant ALEC at the time of intubation and repeated 12 hours later as there was no clinical improvement. Inspite of maximum ventilatory support it became very difficult to keep the arterial oxygen concentration within normal range. At this point the results of septic screening, chest X-ray and Echocardiogram were all normal. The chest X-ray showed mild hyperinflation without any evidence of RDS. Hence, a provisional diagnosis of Persistent Pulmonary hypertension (PPHN) was made. However, there was no improvement in her condition with gradual increase in oxygenation index (OI = MAPx FiO2 /paO2). Baby was transferred to a tertiary referral center and administration of Nitric Oxide followed by Extra Corporeal Membrane Oxygenation (ECMO) was tried. However despite all these the baby died on day 3 of life. A post mortem diagnosis of Surfactant Protein B deficiency was made at the regional center. The post mortem notes revealed normal airway development but bilateral shrinkage of lung volume. The lung tissue was assayed using immuno-histochemical method and was found to have absence of surfactant protein B. There was no other organic involvement apart from mild cardiomegaly. In this baby the diagnosis of surfactant protein B deficiency was thought when the presentation mimicked that of refractory PPHN. Endotracheal secretion assay using the ELISA technique also showed the absence of surfactant protein B. The administration of ALEC did not affect the result as surfactant protein B is inactivated during extraction of artificial surfactants. However, future antenatal screening was planned in view of the diagnosis. Discussion Surfactant therapy has revolutionzed the management of premature infants with respiratory distress syndrome(2). Randomized controlled trials have provided conclusive evidence that surfactant replacement reduces the odds of a baby with RDS having a pneumo-thorax by 30 to 70%, the risk of dying is reduced by 40% and there is increased survival without bronchopulmonary dysplasia(3). Encouraged by this unique success, surfactants are now being used in conditions like meconium aspiration syndrome (to overcome the effect of meconium to neutralize the surfactant in utero). However, the role of surfactant therapy, if any, in relatively mature newborns without RDS is still debatable. It is being empirically used in conditions like PPHN without any conclusive evidence about its efficacy. Phospholipids, primarily dipalmitol phos-phatidyl choline (DPPC) is the main surface tension lowering agent in surfactant. However, DPPC needs surfactant proteins (in endoge-nous and natural surfactants) for efficient dispersion, which enable the formation of a phospholipid monolayer on the alveolar surface. The natural surfactants are derived from extracts of animal lungs and contain two surfactant proteins B and C. A is removed during extraction. In the absence of endogenous surfactant protein B production, the rapid spreading and adsorption of the phospholipid does not take place. This in turn leads to failure of expansion of the alveoli leading to poor cardiorespiratory adaptation at birth. The biochemical defect (absence of surfactant protein B) leads to functionally ineffective surfactant production by the neonate. This leads to poor lung compliance which may secondarily cause persistence of pulmonary hypertension in the neonate. As these babies are more mature they usually do not get exogenous surfactant therapy. Hence the clinical presentation of this condition mimics that of PPHN and is generally refractory to conventional management. It is very difficult to diagnose this condition. Sometimes the history of a sibling death at neonatal period may act as a clue. Absence of surfactant protein B in the amniotic fluid has been shown to be a good screening test for RDS(4). The role of detection of surfactant protein B in the bronchoalveolar lavage has also been explored. However, the diagnosis is commonly a retrospective one in a relatively mature baby with PPHN which was not amenable to treatment. The possibility of this lethal condition should be kep in mind when dealing with a refractory case of PPHN. Though there is no treatment available at present, the role of exogenous surfactant should be explored in future. Theoretically lung transplant appears to be the only hope in these neonates but in most cases the course is so rapidly downhill that there is very little time to contemplate this procedure. It is immensely important to diagnose this condition even with post mortem examination for the sake of future pregnancies Amniotic fluid assay to detect surfactant protein B deficiency is advisable in subsequent pregnancies. This is best done using the ELISA during routine amniocentesis between 16-18 wks. Immunohistochemistry of lung tissue for surfactant protein B and blood test to detect the specific mutation (121 in 2) in surfactant protein B gene by genetic analysis has also been proposed. This mutation was first described by Cole and colleagues and they proposed screening of neonates with refractory respiratory failure for this mutation using high throughput mutation detection system. Contributors: Both SA and KA were directly involved with the management of the case and preparation of the manuscript. SA will act as guarantor for the paper. Funding:
None.
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