The toxic effects of bilirubin on the brain are called bilirubin encephalopathy. The various symptoms of bilirubin encephalopathy are a direct consequence of the damage done to particular neural tissues in the developing brain by bilirubin crossing the blood-brain barrier. Bilirubin toxicity is expressed mostly in the deeper areas of the brain, especially the basal ganglia, hippocampus and the cerebellum, as well as the brainstem. The lesions caused by bilirubin have the effect of causing various disorders of movement and hearing.
Laboratory experiments suggest that developing nerve cells are most susceptible to bilirubin poisoning. Thus, the exact state of development when hyperbilirubinemia occurs influences the kind and severity of the effects on the infant affected. In addition, the levels of bilirubin, especially unbound bilirubin, that are reached and for how long will determine the severity of symptoms, both acute and chronic.
The effects seen while the infant is exposed to high levels of bilirubin are termed acute bilirubin encephalopathy (ABE), while the long term effects that persist after the hyperbilirubinemia has resolved, either naturally or as a result of treatment, are called chronic bilirubin encephalopathy (CBE). The latter is also sometimes simply called kernicterus. Bilirubin-Induced Neurological Dysfunction (BIND) is used to describe long lasting abnormalities that are less obviously debilitating than classic kernicterus or CBE.
Acute Bilirubin Encephalopathy (ABE)
ABE develops progressively in response to the entry of bilirubin into brain tissues. The symptoms at first can be subtle and are not always recognized immediately. The medical literature identifies three phases of ABE, usually termed initial, intermediate and advance.
The initial phase is characterized by the infant not feeding well, being lethargic with a decreased muscle tone (mild hypotonia) and a high pitched cry.
If the hyperbilirubinemia persists, the intermediate phase of ABE shows continued lethargy alternating with irritability and an increase or decrease of muscle tones at different times. Usually there is some arching of the back — the beginnings of retrocollis and/or opisthotonos and the infant has a shrill or high pitched cry and is difficult to console.
The advanced phase is characterized by an intensification of the retrocollis and opisthotonus, producing arching, and inconsolable crying with a shrill cry. If the bilirubin levels are not reduced, the symptoms may progress to seizures or coma and eventually death.
Chronic Bilirubin Encephalopathy (CBE) known as Kernicterus
If bilirubin levels are not reduced in time to prevent neurotoxicity, chronic irreversible encephalopathy is a likely outcome (commonly called kernicterus). The long term effects encompass a range of neuromotor disorders that are referred to as “extrapyramidal” abnormalities because of the particular nerve tracts in the brain that are affected by bilirubin. These disorders can be severe enough to include a form of cerebral palsy and a paralysis of upward gaze. Disturbances of hearing is very characteristic of bilirubin toxicity and may be one of the most sensitive indicators of it, assessed by a technique called auditory brainstem-evoked response (ABR). The disturbance may take the form of difficulties in locating sounds or understanding speech, but may also include actual hearing loss. Dental enamel dysplasia of the deciduous (baby) teeth is also common.
The issue of intellectual handicaps is a difficult one. The literature contains claims that cognitive deficits are a symptom of CBE, but there are other claims that this is solely due to the difficulty of assessing intellectual capacity in children who suffer severe hearing impairment and have difficulties in controlling muscle movements (dystonia).
Bilirubin-Induced Neurological Dysfunction (BIND)
BIND refers to the more subtle signs of bilirubin induced brain injury that are beginning to be recognized. They include learning disabilities that may be caused by disturbances of auditory and speech processing, as well as visual-motor difficulties leading to problems with coordination, balance and muscle tone.
The symptoms of Bilirubin Encephalopathy
Athetosis is a symptom characterized by slow, involuntary, convoluted, writhing movements of the fingers, hands, toes, and feet and in some cases, arms, legs, neck and tongue.
Dystonia is a neurological movement disorder in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures.
Hypertonia is a condition in which there is too much muscle tone so that arms or legs, for example, are stiff and difficult to move
Hypotonia is a medical term used to describe decreased muscle tone
Opisthotonos is caused by spasm of muscles along the spinal column. It can cause infants to “rear backwards” and stiffen out as the mother or nurse attempts to hold or feed them.
Retrocollis is a form of spasmodic torticollis which is in turn a form of focal dystonia, a disorder that is described by sustained muscle contractions causing repetitive and twisting movements, and abnormal postures in a single body region. In Retrocollis there is extension of the neck and the head tilts back.