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Kernicterus is a preventable neurological syndrome caused by deposition of unconjugated bilirubin in the basal ganglia, brainstem nuclei, and cerebellum of neonates, leading to permanent brain damage.

It is the severe manifestation of untreated neonatal hyperbilirubinemia.

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Pathophysiology

Unconjugated bilirubin is lipid-soluble, normally bound to albumin in plasma.
In neonates:
- Albumin binding capacity is low.
- Blood–brain barrier (BBB) is immature → bilirubin crosses more easily.
Precipitating factors:
- Very high serum bilirubin (>20–25 mg/dL in term infants, lower in preterm/ill neonates).
- Hypoxia, sepsis, acidosis, hypoglycemia, hypoalbuminemia, drugs (sulfonamides, ceftriaxone) that displace bilirubin.
Bilirubin deposits in basal ganglia (globus pallidus, subthalamic nuclei), hippocampus, thalamus, cerebellum, cranial nerve nuclei.

Clinical features

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It manifests with lethargy, high-pitched cry, hypotonia → hypertonia, seizures, and leads to long-term motor, auditory, and ocular deficits.

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Clinical stages:

Phase	Feature
Early / Acute Phase
(1st week)	Lethargy, poor feeding, hypotonia, high-pitched cry.
Intermediate Phase	Hypertonia, opisthotonus, retrocollis, fever, irritability.
Late Phase	Seizures, coma, death if untreated.
Chronic Kernicterus
(sequelae)	• Choreoathetoid cerebral palsy.
• Sensorineural hearing loss.
• Gaze abnormalities (especially upward gaze palsy).
• Dental enamel dysplasia.
• Cognitive function may be preserved despite severe motor handicap.

Diagnosis

Primarily clinical with history of severe neonatal jaundice.
Serum bilirubin levels: Risk increases >20–25 mg/dL, but kernicterus may occur at lower levels in preterm infants.

Radiology

MRI brain (in chronic stage):

Bilateral symmetric T2 hyperintensity in globus pallidus and subthalamic nuclei.