Kernicterus

Kernicterus is damage to the brain centers of infants caused by increased levels of unconjugated bilirubin. This may be due to several underlying pathologic processes. Newborn babies are often polycythemic. When they break down the erythrocytes, one of the byproducts is bilirubin, which circulates in the blood and causes jaundice. Alternatively, Rh incompatibility between mother and fetus may cause hemolysis of fetal red blood cells, thereby releasing unconjugated bilirubin into the fetal blood. Since the fetal blood brain barrier is not fully formed, some of this released bilirubin enters the brain and interferes with normal neuronal development. Kernicterus may also be found in infants as a symptom of Crigler-Najjar syndrome type I, a hereditary hyperbilirubinemia resulting in a decreased ability to excrete bilirubin that is fatal within 18 months of life. Other inherited genetic disorders that can contribute to the development of hyperbilirubinemia are Gilbert's syndrome and G6PD deficiency, especially if they are present concurrently.

In adults and older children, jaundice is harmless in and of itself. However, the tissues protecting the brain (the blood-brain barrier) are immature in newborns. Bilirubin penetrates the brain and is deposited in cell bodies (gray matter), especially the basal ganglia, causing irreversible damage. Depending on the level of exposure, the effects range from clinically unnoticeable to severe brain damage and even death.

Some medications, such as the antibiotic co-trimoxazole (a combination of trimethoprim/sulfamethoxazole) may induce this disorder in the baby, either when taken by the mother or given directly to the baby, due to displacement of bilirubin from binding sites on serum albumin. The bilirubin is then free to pass into the Central Nervous System, because the baby's blood-brain barrier is not fully developed.

The only effective way at preventing kernicterus is to lower the serum bilirubin levels either by phototherapy or exchange transfusion.

Symptoms of kernicterus in infants include abnormalities of tone, including hypertonia or hypotonia, lethargy, a distinct, high-pitched cry, and arching of the back (retrocollis or opisthotonus). In children and adults, mild kernicterus manifests through movement and language processing disorders. Furthermore, it mimics autism-spectrum disorders and is often misdiagnosed as such.

The word originates from the German kern, nucleus, kernel, and the Greek ikterus, jaundice.