At what age is a positive Babinski sign considered normal in neonates?

Babinski Sign in Neonates: Normal Developmental Finding

The Babinski sign (extensor plantar response) is physiologically normal in neonates and infants, typically present from birth and persisting until approximately 12-24 months of age, after which it becomes pathological and indicates pyramidal tract dysfunction. 1, 2

Normal Developmental Timeline

The extensor plantar response follows a predictable developmental pattern:

• Birth through first year: The Babinski sign is a normal finding in all healthy neonates and young infants, reflecting the immaturity of the corticospinal (pyramidal) tract 1
• Disappearance timeline: The reflex typically disappears between 12-24 months of age as myelination of the pyramidal tract progresses and cortical inhibition develops 1, 2
• After 24 months: Persistence beyond 2 years of age is generally considered abnormal and warrants neurological evaluation 1

Clinical Interpretation in Neonates

When Babinski is Normal (Expected Finding)

• All neonates and infants under 12 months: A positive Babinski sign (dorsiflexion of the great toe with fanning of the other toes) is the expected normal response 1, 2
• Physiological basis: This reflects incomplete myelination of descending motor pathways, not pathology 1

When to Be Concerned

• Asymmetric response: Unilateral absence or marked asymmetry between sides may indicate focal neurological pathology 3
• Persistence beyond 24 months: Continued presence after age 2 years suggests pyramidal tract dysfunction 1
• Associated abnormal findings: When accompanied by other signs of CNS dysfunction (altered mental status, seizures, abnormal tone, absent primitive reflexes) 3

Important Clinical Pitfalls

Do not misinterpret the normal developmental Babinski sign in infants as pathological - this is one of the most common errors in neonatal neurological examination 1, 2. The presence of an extensor plantar response in a neonate or young infant is developmentally appropriate and does not indicate brain injury or pyramidal tract disease.

Context matters critically: In high-risk neonates (premature infants, those requiring intensive care), the Babinski reflex should be interpreted alongside other primitive reflexes and clinical findings rather than in isolation 3. Studies show that high-risk newborns may present with more frequent abnormal or absent primitive reflex responses, and the clinical significance varies by reflex type 3.

Acute CNS injury caveat: The Babinski sign may be temporarily absent immediately following acute spinal cord transection or acute brain lesions due to spinal shock and temporary inexcitability of spinal motoneurons 1. This does not indicate intact pyramidal function.

Assessment Algorithm for Neonates

When evaluating the plantar response in a neonate:

1. Confirm age appropriateness: Under 12 months = extensor response expected and normal 1
2. Check symmetry: Compare both sides - asymmetry is more concerning than bilateral presence 3
3. Assess other primitive reflexes: Evaluate sucking, Moro, and other age-appropriate reflexes together 3
4. Consider clinical context: In high-risk neonates with abnormal brain imaging, altered mental status, or other focal findings, the Babinski sign gains significance when combined with these abnormalities 3
5. Serial examination: Follow longitudinally - failure to disappear by 24 months warrants investigation 1