Kernicterus is brain damage caused by severe, untreated jaundice or high blood levels of a substance called bilirubin. The condition is typically associated with severe, untreated cases of jaundice in newborns.
Globally, 60 to 80 percent of newborns experience jaundice. In industrialized countries, only 0.4 to 2.7 of every 100, 000 children develop kernicterus or a condition called acute bilirubin encephalopathy. This is where bilirubin levels are so high they spread to the brain and damage the central nervous system tissues.
Currently, kernicterus refers specifically to severe damage to the nervous system caused by jaundice. However, all types of damage related to severe jaundice are also considered to be forms or stages of kernicterus.
In this article, we examine the symptoms of kernicterus, along with its causes and risk factors. We also take a look at how the condition is diagnosed, and what can be done to treat it.
Kernicterus develops from severe, untreated jaundice.
Common symptoms of jaundice, particularly in infants, include:
- yellow or orange-tinted face, whites of the eyes, and gums
- mild difficulty sleeping or being woken up
- reduced urine production or dark-colored urine
- trouble breast-feeding, suckling a bottle, or eating
- mild fussiness and difficult to soothe
Babies with mild to moderate jaundice often have no symptoms besides the yellow tint to their eyes and skin.
In severe jaundice, the change in color that affects the face, whites of the eyes, and gums in mild jaundice progress to the rest of the body, moving down through the chest, belly, legs, and arms.
Common symptoms of severe jaundice and kernicterus include:
- stiff, limp, or floppy body
- high-pitched, continual crying
- strange or uncoordinated eye movements
- body arching like a bow, with the head, neck, and heels bent backward, and the rest of the body angled forward
- bulging of the soft spot on the top of a baby's head
People should seek immediate medical attention any time they suspect symptoms of severe jaundice or kernicterus.
The body produces bilirubin when old red blood cells are broken down.
Once free in the bloodstream, bilirubin is taken up by the liver, made water-soluble, then excreted into bile salts.
Bilirubin is then broken down by intestinal bacteria. It then either leaves the body in the feces or is transported to the kidneys and removed from the body in urine.
In newborns, the organs may not be developed enough to process bilirubin, especially in the first few hours and days of life. This can result in jaundice.
High blood levels of bilirubin, beyond the newborn stage, are often a sign of disease or damage to the liver, as this organ is primarily responsible for clearing bilirubin from the blood.
Kernicterus occurs when bilirubin levels in the blood become so high that it crosses the blood-brain barrier and damages the brain tissue. The condition is almost always related to severe jaundice.
Common causes of significant jaundice include:
- underdeveloped, diseased, or damaged liver
- destruction of red blood cells, often when the mother's blood type does not match her baby's
- premature birth, typically before 37 weeks of gestation or pregnancy
- increased bilirubin production
- Gilbert's syndrome, a condition that leads to high bilirubin levels
- bile duct obstruction or blockage
Though mild jaundice is very common in newborns, some factors are known to increase the risk of severe jaundice and kernicterus significantly.
Risk factors for kernicterus include:
- mother and child not sharing a blood group
- lack of glucose-6-phosphate dehydrogenase (G6PD), an enzyme that helps red blood cells to work properly
- low birth weight
- premature birth
- dark skin color, as yellowing skin is hard to notice
- feeding trouble or poor appetite
- bruising or bruising conditions
- family history of jaundice
- bruising or injuries from a difficult birth
Though many of these conditions can increase a baby's risk for severe jaundice, prompt treatment of high bilirubin levels can almost always prevent kernicterus.
Does it affect adults and children differently?
Cases of kernicterus involving adults are considered very rare, and only a few have been reported.
Kernicterus is usually considered far more likely to impact infants because their blood-brain barrier is not fully developed.
Infants are also more prone to severe jaundice and kernicterus because their livers are not fully developed and are less capable of removing bilirubin from the blood.
Kernicterus can cause serious, permanent, health complications related to brain damage.
A 2014 study followed 128 individuals treated for severe jaundice at birth for 30 years. The authors found that
Complications associated with kernicterus include:
- hearing loss or difficulty processing sounds
- vision problems
- undeveloped teeth and jaw bones
- movement disorders caused by brain damage
- intellectual and developmental disabilities, including dyslexia
- stained baby teeth
- autistic spectrum disorders
- inattention and hyperexcitability disorders, especially in early childhood
If left untreated, kernicterus can lead to coma and death.
In newborns, a nurse or doctor will often initially test for jaundice by placing a light meter on the baby's forehead. Doing so gives them a transcutaneous bilirubin (TcB) level reading. If the TcB level is high, a blood test will be done.
In infants, doctors usually perform a bilirubin blood test by taking a blood sample from the heel.
This enables the doctor to obtain a reading for the total serum bilirubin (TSB) level.
In most hospitals, it is routine to test a newborn's TcB levels every 8 to 12 hours in the first 48 hours of life, and at least once more at 3 to 5 days old.
Though the standard varies between hospitals and doctors, newborns are diagnosed with jaundice when they have bilirubin blood levels greater than 85 micromoles per liter (μmol/L). This translates to 5 milligrams per deciliter (mg/dl).
Bilirubin blood levels are usually the highest when a baby is between 3 and 5 days old.
If jaundice is diagnosed, additional blood samples may be required every few hours to check the condition's progress and to see how effective treatment is if it is needed.
How aggressively jaundice is treated depends on the baby's age measured in hours, and how high bilirubin levels have risen. Kernicterus is always treated in a hospital immediately.
Most babies with jaundice at levels that warrant treatment, and all babies with kernicterus, are placed in an incubator, under special lights with their eyes covered.
The baby will also require more milk or formula, often with feedings every 2 hours. In some cases, a feeding tube may be placed in the child's throat to allow direct feeding. Hydrating fluids are also commonly given through a vein.
For severe cases of jaundice, and usually all cases of kernicterus, a blood transfusion is immediately done to lower the amount of free bilirubin in the blood.
Once kernicterus has developed, the specific treatment options depend on the symptoms.
Common treatments used for the complications of kernicterus include:
Jaundice is easily treatable when diagnosed and treated early enough, or while still in its mild forms. Once kernicterus has occurred, however, the resulting problems are usually permanent, though some may lessen or go away with therapy, medication, or in adulthood.
People should seek immediate medical attention anytime that the symptoms of jaundice or kernicterus occur. It can take less than 24 hours for serious cases of jaundice to progress to kernicterus.
New technologies are being developed to help make it easier for parents and caregivers to detect jaundice in newborns earlier. These include a mobile phone app called the BiliScan.