Clinical Features of Kernicterus
Kernicterus presents as a chronic neurological syndrome characterized by athetoid cerebral palsy, auditory dysfunction (including auditory neuropathy/dys-synchrony), dental-enamel dysplasia, and paralysis of upward gaze, typically developing in infants who survived acute bilirubin encephalopathy. 1
Acute Phase: Bilirubin Encephalopathy
Before chronic kernicterus develops, infants progress through acute bilirubin encephalopathy with three distinct phases 1:
Early Phase
- Lethargy
- Hypotonia (decreased muscle tone)
- Poor sucking/feeding
Intermediate Phase
- Moderate stupor
- Irritability
- Hypertonia (increased muscle tone)
- Fever
- High-pitched cry alternating with drowsiness
- Retrocollis (backward arching of neck)
- Opisthotonos (backward arching of trunk)
Clinical Pearl: Emergency exchange transfusion at this stage may still reverse CNS changes in some cases 1
Advanced Phase (Irreversible CNS Damage)
- Pronounced retrocollis-opisthotonos
- Shrill cry
- Complete feeding refusal
- Apnea
- Fever
- Deep stupor progressing to coma
- Seizures (sometimes)
- Death (possible)
Chronic Kernicterus: The Classic Tetrad
Surviving infants develop the following permanent features 1:
1. Motor Dysfunction
- Severe athetoid cerebral palsy (most prominent feature)
- Dystonic posturing (recognized within 6 months corrected age) 2
2. Auditory Dysfunction
- Hearing loss
- Auditory neuropathy/auditory dys-synchrony (AN/AD) 3
- Abnormal brainstem auditory evoked potentials in 7 of 10 patients 4
3. Oculomotor Abnormalities
- Paralysis of upward gaze (pathognomonic finding)
4. Dental Abnormalities
- Dental-enamel dysplasia
5. Less Common Features
- Intellectual disability (less frequent than motor/auditory findings)
- Other neurological handicaps 1
Diagnostic Imaging Findings
MRI shows characteristic bilateral hyperintensity in the globus pallidus, though the pattern evolves with age 5, 4:
- Neonatal period (2 weeks): T1-weighted hyperintensity in globus pallidus
- Infancy (9-26 months): Diffuse T2-weighted hyperintensity throughout entire globus pallidus
- After 2 years: T2-weighted hyperintensity limited to the borders of globus pallidus
- May also involve posteromedial globus pallidus and subthalamic nucleus 4
Critical Caveat: A "blind window" exists during early infancy (around 2 months) where MRI may appear normal despite kernicterus 5, 2. MRI abnormalities in infancy (performed in 7 preterm infants) showed bilateral globi pallidi lesions, but neonatal or post-1-year MRI showed no abnormalities 2.
Important Clinical Considerations
Silent Presentation Warning
Occasionally, infants develop very high bilirubin levels and subsequent kernicterus without exhibiting antecedent clinical signs of acute bilirubin encephalopathy 1. This makes universal systematic screening essential rather than relying on clinical observation alone.
Preterm Infant Presentation
In preterm infants (≤34 weeks), kernicterus features are similar but with notable differences 2:
- No classical acute encephalopathy symptoms during neonatal period
- Dystonic posture first recognized within 6 months corrected age
- Peak bilirubin levels may be lower (only 3 of 8 had >15 mg/dL)
- Gestational age ≤26 weeks in 6 of 8 cases
Spectrum of Severity
Modern understanding recognizes kernicterus exists on a spectrum (Kernicterus Spectrum Disorder) 6:
- Motor-predominant kernicterus (classic presentation)
- Auditory neural sensory dysfunction (isolated hearing loss)
- Subtle kernicterus (mild neurological dysfunction)
- Kernicterus plus (additional complications)
The clinical expression varies with location, severity, and timing of bilirubin exposure, influenced by amount, duration, and developmental age at exposure 3.