Ordinarily, substances toxic to the brain cells are kept safely bottled up in the bloodstream by the "blood-brain barrier," which relates to the fact that the lining cells of the blood vessels of the brain are very selective about what substances they allow to pass from the bloodstream into the brain tissue. Certain toxic substances, and even many drugs, are thus excluded from the brain tissue.

Very high levels of "unconjugated" (unprocessed) bilirubin (the waste product of hemoglobin breakdown from old red blood cells) can harm the infant brain. This waste product selectively stains and damages the part of the brain known as the basal ganglia. These areas control the fluidity of muscle movement. Kernicterus is the technical name for the specific form of brain damage due to excessive levels of bilirubin in the bloodstream.

Because of this dreadful possibility, jaundice in babies is monitored closely. There is no absolute level of jaundice that is guaranteed to be dangerous, but intervention (either phototherapy or exchange transfusion) is usually done at about a level of "20" (the units are milligrams of bilirubin per 100 cc of blood, or mg/dl).

Because the damage inflicted by excessive bilirubin concentrations is directed chiefly against the basal ganglia and other areas of the brain (hippocampus, geniculate bodies, various brainstem nuclei, and the cerebellum) with their crucial role in controlling motor movement - kernicterus was once the leading cause of athetoid (writhing) cerebral palsy. Because of the largely effective control of newborn jaundice, athetosis is now a relatively rare form of cerebral palsy. The syndrome in term infants is marked by refusal to feed, a high-pitched cry, stiffness, and arching of the back. Survivors usually suffer not only athetoid cerebral palsy, but high-frequency hearing loss, paralysis of upward gaze, and dental enamel malformations.

Kernicterus still occurs very rarely, mainly in very tiny, very sick prematures or in term babies with jaundice aggravated by illness, nursing failure and dehydration, parental ignorance or poor medical followup. Prevention is a medical issue and involves

  • sensitivity of doctors and nurses to jaundice appearing in the newborn nursery
  • education of parents about jaundice
  • most importantly, the provision of good followup care and readily available counsel for parents
  • readily available access to medical followup examination of newborns just home from the hospital

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