Neonatal kernicterus is a severe, preventable form of brain damage that can occur in newborns. It arises from dangerously high levels of bilirubin, a yellow pigment, accumulating in the baby’s bloodstream and subsequently affecting the brain.
Understanding Jaundice and Bilirubin
Bilirubin is a yellowish pigment produced when red blood cells break down, a natural process in the body. In adults, the liver processes bilirubin, converting it into a water-soluble form that can be excreted in bile and stool. Newborns, however, have an immature liver that is less efficient at processing bilirubin, and they also have a higher rate of red blood cell breakdown, leading to increased bilirubin production. This combination often results in a buildup of bilirubin in their blood.
The accumulation of bilirubin causes neonatal jaundice, characterized by a yellowing of the baby’s skin and the whites of their eyes. Most newborns experience physiological jaundice, a common and usually harmless condition that typically appears on the second or third day of life and resolves within two weeks. Pathological jaundice, in contrast, is more concerning as it can indicate an underlying disorder or dangerously high bilirubin levels requiring medical attention. Risk factors for severe jaundice include:
- Prematurity (babies born before 38 weeks of gestation).
- Significant bruising during birth.
- Blood group incompatibilities, such as Rh hemolytic disease.
- Certain genetic conditions, including Gilbert syndrome or G6PD deficiency.
The Brain Damage Caused by Kernicterus
When unconjugated bilirubin, the form not yet processed by the liver, reaches excessively high levels in the bloodstream, it can cross the blood-brain barrier. This barrier normally protects the brain from harmful substances, but it is less developed in newborns, making them more vulnerable. Once in the brain tissue, bilirubin primarily deposits in specific areas, most notably the basal ganglia, which are responsible for motor control. Other affected regions can include the hippocampus, thalamus, and cranial nerve nuclei.
The deposition of bilirubin in these brain regions leads to neurotoxicity, causing irreversible damage to brain cells. This cellular damage disrupts normal brain function, resulting in the characteristic neurological impairments associated with kernicterus. The extent of damage is influenced by bilirubin concentration, duration of exposure, and individual susceptibility factors like prematurity, acidosis, or infection. This severe brain injury is also referred to as bilirubin encephalopathy.
Recognizing Kernicterus: Signs and Long-Term Effects
Early recognition of kernicterus signs is important, as timely intervention can prevent severe, permanent damage. Initial symptoms, often appearing within the first few days, include extreme lethargy, poor feeding, and a high-pitched cry. The baby may also exhibit low muscle tone and a diminished or absent startle reflex. These early signs can be subtle and sometimes mistaken for general newborn behaviors, but their persistence warrants immediate medical evaluation.
As kernicterus progresses, symptoms become more severe. Middle-stage signs can include irritability, increased muscle tone leading to arching of the back and neck (opisthotonus), and continued poor feeding. In the late stages, infants may experience seizures, muscle rigidity, stupor, or even coma. Abnormal eye movements, such as an inability to gaze upwards or side-to-side, may also become apparent.
If untreated or if significant brain damage occurs, kernicterus can lead to severe and lasting neurological impairments. Long-term effects include:
- Various forms of cerebral palsy, particularly athetoid cerebral palsy, which involves involuntary, uncontrolled movements.
- Hearing loss, ranging from mild to profound, and auditory neuropathy (problems processing sounds).
- Intellectual disabilities.
- Developmental delays.
- Problems with speech.
- Dental enamel dysplasia, affecting tooth development.
Preventing and Treating Kernicterus
Preventing kernicterus begins with careful monitoring and timely intervention for jaundice in newborns. Universal screening for jaundice is a standard practice before hospital discharge, typically involving a visual inspection and/or measurement of bilirubin levels using a transcutaneous bilirubinometer (TcB) or a total serum bilirubin (TSB) blood test. These measurements help identify infants at risk of developing severe hyperbilirubinemia, especially those discharged early. Follow-up appointments are usually scheduled within two days of discharge for babies sent home before 72 hours of age.
The primary treatment for high bilirubin levels is phototherapy, which involves exposing the newborn’s skin to a special blue-green light. This light penetrates the skin and converts unconjugated bilirubin molecules into water-soluble isomers, such as Z-lumirubin, that can be more easily excreted by the liver and kidneys through urine and stool. Phototherapy is a safe and effective method for reducing bilirubin levels and typically reduces the need for more invasive treatments. Babies undergoing phototherapy are usually unclothed, save for a diaper, and wear eye covers to protect their eyes from the light.
For very severe cases of hyperbilirubinemia, especially when phototherapy is insufficient or signs of acute bilirubin encephalopathy are present, an exchange transfusion may be necessary. This procedure involves slowly removing small aliquots of the baby’s bilirubin-rich blood and simultaneously replacing them with an equal amount of compatible donor blood. This process effectively removes excess bilirubin, antibodies, and abnormal red blood cells from the infant’s circulation. Exchange transfusions are typically performed over two to three hours, often through umbilical catheters. Timely medical intervention with phototherapy or exchange transfusion is important to prevent the irreversible brain damage associated with kernicterus.