How mild is the outcome of mild neonatal encephalopathy?

Abstract

Over 4 decades ago, Sarnat defined stage I, or mild, neonatal encephalopathy following fetal distress as a postanoxic state characterized by a hyperalert level of consciousness with normal muscle tone on exam, no clinical seizures, and a normal EEG (Arch Neurol 1976;33:696-705). In that report of just 21 patients >36 weeks' gestation with fetal distress and investigator-defined stage I mild to stage III severe encephalopathy, those neonates with <5 days in stage II moderate encephalopathy and a predominance of stage I findings were all developmentally normal subsequently at age 12 months. The derivative conclusion was that newborns with mild neonatal encephalopathy are largely developmentally normal months later. Since then, many changes in neonatal care have taken place, including technology to rescue younger and sicker term and preterm babies, use of surfactant for lung immaturity, and implementation of neonatal hypothermia for babies with neonatal encephalopathy, acidosis, and gestational age 34 to 35 weeks. But is mild neonatal encephalopathy truly associated with mildly abnormal or normal outcomes when larger samples of newborns are examined, especially after the application of therapeutic hypothermia for concerns of distress, acidosis, or seizures with decreasing gestational age? In this volume of The Journal, Walsh et al report a limited, single institution, historical cohort study of 89 neonates >34 weeks' gestation with neonatal encephalopathy and pH <7.1, all treated with hypothermia. The investigators sought to determine whether magnetic resonance imaging detected brain abnormalities after hypothermia were any different among those with mild, moderate, or severe neonatal encephalopathy, based upon more modern grading criteria. They studied 48 infants with mild encephalopathy, with 35 moderate, yet just 6 with severe neonatal encephalopathy. Although this team did find in their sample proportionately more acute basal ganglia and thalamic abnormalities in those neonates with severe encephalopathy after therapeutic hypothermia, they could not detect any differences in the rate of overall brain abnormalities demonstrated by brain magnetic resonance imaging after hypothermia. Their finding is provocative but based on an early exploration. Their conclusions derive from a small, retrospective sample with limited power to detect a difference and the potential for a type II error. The findings of Walsh et al are intriguing and should spur further research into both the radiographic and clinical outcomes of mild encephalopathy after therapeutic hypothermia. More comprehensive, long-term data are needed to delineate the neurological and developmental outcome of newborns with mild neonatal encephalopathy, with and without therapeutic hypothermia. Article page 26 ▶ The Frequency and Severity of Magnetic Resonance Imaging Abnormalities in Infants with Mild Neonatal EncephalopathyThe Journal of PediatricsVol. 187PreviewTo assess and contrast the incidence and severity of abnormalities on cerebral magnetic resonance imaging (MRI) between infants with mild, moderate, and severe neonatal encephalopathy who received therapeutic hypothermia. Full-Text PDF