Kernicterus (Neonatal Jaundice)

What is Kernicterus (Neonatal Jaundice)?

Kernicterus is a rare but serious form of brain damage that can occur in newborns with severe, untreated hyperbilirubinemia (high levels of bilirubin in the blood). Bilirubin is a yellow pigment produced when red blood cells break down. In most babies, the liver matures quickly enough to convert bilirubin into a form that can be eliminated in stool and urine. When this process is overwhelmed, bilirubin accumulates, leading to jaundice (skin and eye yellowing). If bilirubin levels continue to rise, the pigment can cross the immature blood‑brain barrier and deposit in the basal ganglia and other brain regions, causing permanent neurological injury—this is kernkernicterus.

While “neonatal jaundice” describes the visible yellow discoloration, kernicterus refers specifically to the neurotoxic effects of extremely high bilirubin. Early recognition and treatment of jaundice are essential to prevent this complication.

Key points:

• Occurs most often within the first week of life.
• Risk is higher in premature infants, those with blood‑type incompatibilities, or certain genetic enzyme deficiencies.
• Prompt phototherapy or exchange transfusion can reverse jaundice and prevent kernicterus.

Common Causes

Several conditions can lead to excessive bilirubin production or reduced clearance, increasing the risk of kernicterus. The most common include:

• Physiologic newborn jaundice: Normal breakdown of fetal hemoglobin; peaks at 3–5 days.
• Breast‑feeding jaundice: Inadequate milk intake → dehydration and reduced bilirubin excretion.
• Breast‑feeding jaundice (late onset): Maternal milk factors that inhibit bilirubin conjugation.
• Hemolytic disease of the newborn (HDN): ABO or Rh incompatibility leading to rapid red‑cell destruction.
• G6PD deficiency: Enzyme defect causing episodic hemolysis, especially after oxidative stress.
• Hereditary spherocytosis or pyruvate kinase deficiency: Chronic hemolysis.
• Crigler‑Najjar syndrome type I: Absence of the enzyme UDP‑glucuronosyltransferase‑1A1 (UGT1A1) → severe unconjugated hyperbilirubinemia.
• Gilbert’s syndrome (rare in newborns): Mild UGT1A1 deficiency that can exacerbate other causes.
• Sepsis or severe infection: Impairs hepatic function and increases hemolysis.
• Birth trauma (e.g., cephalo‑hematoma): Leads to internal bleeding and increased bilirubin load.

Associated Symptoms

Before bilirubin reaches neurotoxic levels, the most noticeable sign is jaundice. As levels climb, other systemic and neurological signs may appear:

• Yellowing of the skin and sclera: Starts on the face and progresses downward.
• Lethargy or poor feeding: Newborn may be unusually sleepy or weak.
• High‑pitched cry: Irritability with a piercing cry.
• Temperature instability: May become hypothermic or have fever.
• Hypotonia (floppy baby): Decreased muscle tone.
• Seizures: May be focal or generalized, indicating central nervous system involvement.
• Abnormal eye movements: Nystagmus or inability to track objects.
• Auditory dysfunction: High‑frequency hearing loss can develop later.
• Movement disorders: Post‑kernicterus, children may develop athetoid cerebral palsy, choreoathetoid movements, or dystonia.

When to See a Doctor

Because kernicterus can develop rapidly, parents and caregivers should seek medical attention promptly if any of the following occur:

• Jaundice that spreads to the abdomen or limbs within the first 24‑48 hours of life.
• Yellowing of the eyes (scleral icterus) at any age.
• Baby is difficult to awaken, unusually sleepy, or not feeding well.
• Persistent high‑pitched cry or irritability that does not improve with feeding.
• Temperature < 36.0 °C (96.8 °F) or > 38.0 °C (100.4 °F) in a newborn with jaundice.
• Any seizure‑like activity (stiffening, rhythmic jerking, staring).
• Parents have a known blood‑type incompatibility (e.g., Rh‑negative mother, Rh‑positive baby).

Diagnosis

Evaluation combines clinical examination with laboratory testing:

1. Physical exam

Clinician assesses the extent of skin and scleral yellowing using the cephalocaudal progression rule and checks for signs of dehydration, lethargy, or neurologic changes.

2. Serum bilirubin measurement

Blood is drawn to measure total serum bilirubin (TSB) and differentiate between:

• Unconjugated (indirect) bilirubin: Most common in newborn hyperbilirubinemia; the primary toxin in kernicterus.
• Conjugated (direct) bilirubin: Suggests liver disease or obstruction; less likely to cause kernicterus.

The result is plotted on an age‑specific bilirubin nomogram (Bhutani chart) to determine risk level.

3. Additional labs (as indicated)

• Complete blood count (CBC) – to detect anemia or hemolysis.
• Blood type and Coombs test – to identify immune hemolysis.
• G6PD assay – especially in populations with higher prevalence.
• Liver function tests – ALT, AST, GGT.
• Blood cultures – if infection is suspected.

4. Neurologic assessment

If bilirubin is > 20 mg/dL (≈ 340 µmol/L) or the infant shows neurologic signs, a bedside auditory brainstem response (ABR)** or **MRI** may be ordered to evaluate for kernicterus.