Acute bilirubin encephalopathy (ABE) is a neurological condition in newborns with severe jaundice. It occurs when bilirubin, a substance from the natural breakdown of red blood cells, reaches dangerously high levels, a state known as hyperbilirubinemia. While most newborn jaundice is harmless, ABE is the acute phase of brain damage from bilirubin toxicity. If not treated urgently, it can lead to permanent brain injury.
The Link Between Jaundice and Brain Injury
Normally, the liver processes bilirubin, making it water-soluble for excretion. In newborns, the liver is still maturing and may not handle this process efficiently, leading to a temporary bilirubin buildup. This causes the common yellowing of the skin and eyes known as jaundice, which is typically mild and resolves on its own.
Hyperbilirubinemia can happen for reasons that accelerate red blood cell breakdown or impair the liver. A significant risk factor is blood type incompatibility between the mother and infant, such as Rh or ABO incompatibility. In these cases, the mother’s antibodies attack the baby’s red blood cells, causing rapid breakdown and releasing large amounts of bilirubin.
Other risk factors include inherited conditions like G6PD deficiency, which makes red blood cells fragile, and prematurity, as the liver is less developed. Significant bruising from a difficult birth can also release excess bilirubin as the pooled blood breaks down.
When the concentration of fat-soluble bilirubin overwhelms a protein called albumin in the blood, it can cross the newborn’s developing blood-brain barrier. This barrier is more permeable in infants. Once in the brain, bilirubin is toxic to nerve cells, depositing in areas like the basal ganglia and brainstem and causing the neurological damage of ABE.
Recognizing the Warning Signs
The symptoms of ABE progress through phases if bilirubin levels are not reduced, reflecting increasing toxicity in the brain. Recognizing these signs early is necessary to prevent permanent injury, as the condition can worsen over days or even hours.
The initial phase is subtle and can be mistaken for other newborn issues. An infant may become very sleepy, lethargic, and difficult to wake for feedings. They often exhibit low muscle tone (hypotonia), feeling “floppy” when held, and may have a poor or weak suck.
In the intermediate phase, symptoms become more alarming. The infant may be irritable with a high-pitched cry and alternate between lethargy and rigidity (hypertonia). A characteristic sign is the arching of the back and neck, a posture known as opisthotonos.
The advanced phase is a medical emergency representing severe brain involvement. The infant may stop feeding, develop a fever, and fall into a stupor or coma. The muscle arching can become more pronounced, and pauses in breathing (apnea) or seizures may occur. Without immediate treatment, the damage can become irreversible.
Urgent Medical Treatment
The primary goal of treating ABE is to rapidly lower the bilirubin level in the infant’s blood. The main interventions are intensive phototherapy and exchange transfusion, with the choice depending on the severity and the infant’s condition.
Intensive phototherapy is often the first line of treatment. This process involves placing the naked infant under special blue-green lights. The light penetrates the skin and converts the toxic bilirubin into a water-soluble form that can be excreted in urine and stool without being processed by the liver. To maximize effectiveness, as much of the infant’s skin as possible is exposed to the light.
If phototherapy is not effective enough, or if the infant shows signs of neurological damage, an exchange transfusion may be necessary. This procedure involves slowly removing small amounts of the infant’s blood and replacing it with donor blood. This directly removes both bilirubin and any maternal antibodies causing red blood cell destruction, rapidly lowering bilirubin levels.
Potential Long-Term Effects
When ABE is not treated in time and causes permanent brain damage, the resulting chronic condition is known as kernicterus. This term describes the permanent neurological syndrome caused by bilirubin toxicity. The effects of kernicterus become apparent as the child grows and develops.
The classic signs of kernicterus form a distinct set of permanent neurological impairments. These include:
- A form of cerebral palsy (athetoid or dyskinetic) characterized by slow, involuntary movements and sustained muscle contractions.
- Hearing problems, ranging from mild loss to complete deafness, due to auditory nerve damage.
- Difficulties with eye movements, particularly an inability to gaze upwards.
- Dental enamel dysplasia, where the enamel of baby teeth is discolored or poorly formed.