Prevention of bilirubin encephalopathy

Bilirubin Encephalopathy

PURPOSE OF REVIEW

Hyperbilirubinemia is commonly seen in neonates. Though hyperbilirubinemia is typically asymptomatic, severe elevation of bilirubin levels can lead to acute bilirubin encephalopathy and progress to kernicterus spectrum disorder, a chronic condition characterized by hearing loss, extrapyramidal dysfunction, ophthalmoplegia, and enamel hypoplasia. Epidemiological data show that the implementation of universal pre-discharge bilirubin screening programs has reduced the rates of hyperbilirubinemia-associated complications. However, acute bilirubin encephalopathy and kernicterus spectrum disorder are still particularly common in low- and middle-income countries.

RECENT FINDINGS

The understanding of the genetic and biochemical processes that increase the susceptibility of defined anatomical areas of the central nervous system to the deleterious effects of bilirubin may facilitate the development of effective treatments for acute bilirubin encephalopathy and kernicterus spectrum disorder. Scoring systems are available for the diagnosis and severity grading of these conditions. The treatment of hyperbilirubinemia in newborns relies on the use of phototherapy and exchange transfusion. However, novel therapeutic options including deep brain stimulation, brain-computer interface, and stem cell transplantation may alleviate the heavy disease burden associated with kernicterus spectrum disorder. Despite improved screening and treatment options, the prevalence of acute bilirubin encephalopathy and kernicterus spectrum disorder remains elevated in low- and middle-income countries. The continued presence and associated long-term disability of these conditions warrant further research to improve their prevention and management.

High unbound bilirubin for age: a neurotoxin with major effects on the developing brain

Neonatal hyperbilirubinemia is one of the most frequent diagnoses made in neonates. A high level of unconjugated bilirubin that is unbound to albumin is neurotoxic when the level exceeds age-specific thresholds or at lower levels in neonates with neurotoxic risk factors. Lower range of unbound bilirubin results in apoptosis, while moderate-to-high levels result in neuronal necrosis. Basal ganglia and various brain stem nuclei are more susceptible to bilirubin toxicity. Proposed mechanisms of bilirubin-induced neurotoxicity include excessive release of glutamate, mitochondrial energy failure, release of proinflammatory cytokines, and increased intracellular calcium concentration. These mechanisms are similar to the events that occur following hypoxic-ischemic insult in neonates. Severe hyperbilirubinemia in term neonates has been shown to be associated with increased risk for autism spectrum disorders. The neuropathological finding of bilirubin-induced neurotoxicity also includes cerebellar injury with a decreased number of Purkinje cells, and disruption of multisensory feedback loop between cerebellum and cortical neurons which may explain the clinical characteristics of autism spectrum disorders. Severe hyperbilirubinemia occurs more frequently in infants from low- and middle-income countries (LMIC). Simple devices to measure bilirubin, and timely treatment are essential to reduce neurotoxicity, and improve outcomes for thousands of neonates around the world.

Management of neonatal hyperbilirubinemia: pediatricians' practices and educational needs

Background

Early detection and treatment of neonatal hyperbilirubinemia is important in the prevention of bilirubin-induced encephalopathy. In this study, we evaluated the New Jersey pediatricians' practices and beliefs regarding the management of neonatal hyperbilirubinemia and their compliance with the recommendations made by the American Academy of Pediatrics (AAP) in 1994.

Methods

A survey questionnaire was mailed to a random sample of 800 pediatricians selected from a list of 1623 New Jersey Fellows of the AAP initially in October 2003 and then in February 2004 for the non-respondents. In addition to the physicians' demographic characteristics, the questionnaire addressed various aspects of neonatal hyperbilirubinemia management including the diagnosis, treatment, and follow up as well as the pediatricians' beliefs regarding the significance of risk factors in the development of severe hyperbilirubinemia.

Results

The adjusted response rate of 49.1% (n = 356) was calculated from the 725 eligible respondents. Overall, the practicing pediatricians reported high utilization (77.9%) of the cephalocaudal progression of jaundice and low utilization (16.1%) of transcutaneous bilirubinometry for the quantification of the severity of jaundice. Most of the respondents (87.4%) identified jaundice as an indicator for serum bilirubin (TSB) testing prior to the neonate's discharge from hospital, whereas post-discharge, only 57.7% felt that a TSB was indicated (P < 0.01). If the neonate's age was under 72 hours, less than one-third of the respondents reported initiation of phototherapy at TSB levels lower than the treatment parameters recommended by the AAP in 1994, whereas if the infant was more than 72 hours old, almost 60% were initiating phototherapy at TSB lower than the 1994 AAP guidelines. Most respondents did not regard neonatal jaundice noted after discharge and gestational ages 37–38 weeks as being significant in the development of severe hyperbilirubinemia. However, the majority did recognize the importance of jaundice presenting within the first 24 hours and Rh/ABO incompatibility.

Conclusion

The pediatricians' practices regarding the low utilization of laboratory diagnosis for the quantification of jaundice after discharge and underestimation of risk factors that contribute to the development of severe hyperbilirubinemia are associated with initiation of phototherapy at lower than AAP recommended treatment parameters and recognition of neonatal hyperbilirubinemia as an important public health concern.

Neurological complications of kernicterus

OBJECTIVE AND BACKGROUND

Prevention of bilirubin encephalopathy relies on the detection of newborns who are at risk of developing serious hyperbilirubinemia. The objective of this study was to reassess the clinical syndrome of kernicterus as neurodiagnostic studies have become more readily available and can be used to evaluate these infants.

METHODS

The study population was neonates born at term or near term admitted to The Hospital for Sick Children in Toronto, Ontario, Canada, between January 1990 and May 2000. During the study period, there were 9776 admissions (average number of admissions per year--888 infants). The inclusion criteria were that patients had total serum bilirubin levels of >400 micromol/L at the time of diagnosis and no evidence of hypoxic ischemic encephalopathy. Records were reviewed to establish neurodevelopment outcomes.

RESULTS

Twelve neonates (nine males) were identified. Bilirubin levels at the time of diagnosis ranged from 405 to 825 micromol/L. Causes of these elevated levels included glucose-6-phosphate dehydrogenase deficiency (seven patients), dehydration (three patients), sepsis (one patient), and was undetermined in one patient. Abnormal visual evoked potentials were found in three of nine patients and abnormal brainstem auditory evoked potentials in seven of ten patients. Abnormal electroencephalograms were documented in five patients studied. Brain magnetic resonance imaging results were abnormal in three of four patients.

CONCLUSIONS

Magnetic resonance imaging typically showed an increased signal in the posteromedial aspect of the globus pallidus and was, therefore, useful in the assessment of the structural changes of chronic bilirubin encephalopathy after kernicterus.