Primitive Reflexes

Overview

• Reflexes normally present in infants.
• Disappear progressively as child develops.
• Mediated by brainstem and spinal cord.
• Suppression occurs via maturation of higher cortical centers.
• Appearance and disappearance follow specific developmental timelines.
• Essential component of neonatal and infant neurological examination.
• Provide crucial information regarding central nervous system (CNS) integrity.
• Absence, asymmetry, or persistence beyond expected age signifies CNS dysfunction.

Prerequisites for Testing

• Infant must be alert (State 3-5: eyes open, responsive).
• Infant must not be irritable.
• Minimum 2 hours post-feeding.
• Head positioned in midline during assessment to prevent tone alteration.

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Chronology of Primitive Reflexes

Reflex	Onset (Gestational Age)	Fully Developed	Duration/Disappearance (Postnatal)
Palmar Grasp	28 weeks	32 weeks	2–3 months (up to 6 months)
Rooting	32 weeks	36 weeks	3–4 months
Moro	28–32 weeks	37 weeks	5–6 months
Tonic Neck (ATNR)	35 weeks	1 month	5–6 months
Parachute	7–8 months	10–11 months	Remains throughout life

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Specific Reflexes: Elicitation and Interpretation

1. Moro Reflex

• Elicitation Method 1: Support infant in semierect position. Allow head to fall backward onto examiner’s hand.
• Elicitation Method 2: Support head in midline with one hand, back with the other. Raise infant to 45°. Let head fall through 10°. Repeat three times.
• Normal Response:
  • Phase 1 (Abduction and Extension): The infant abruptly abducts and extends the arms, spreading them outward. The hands open, and the fingers flare, typically with the thumb and index finger forming a distinct “C” shape.
  • Phase 2 (Adduction and Flexion): The infant then brings the arms back toward the midline in a smooth, clasping, or embracing motion, often flexing the arms over the chest.
• Clinical Nuances:
  • Absent in term newborn: Ominous sign. Suggests significant diffuse CNS dysfunction.
  • Asymmetric response: Indicates local pathology. Fractured clavicle, brachial plexus injury, or hemiparesis.
  • Abnormal Moro: Constitutes a neonatal neurological alarm sign.

2. Palmar Grasp and Traction Response

• Elicitation: Place index finger into infant’s open palm. Gently press palmar surface. Avoid touching dorsal surface.
• Normal Response: Forced grasp of examiner’s finger.
• Traction Component: By 37 weeks gestation, grasp is strong enough to lift infant from bed with gentle traction.
• Clinical Nuances:
  • Tests distal power.
  • Asymmetry suggests unilateral weakness or lower motor neuron lesion.
  • Persistence beyond 6 months indicates spasticity or upper motor neuron (UMN) lesion.

3. Asymmetric Tonic Neck Reflex (ATNR)

• Elicitation: Infant in supine position. Manually rotate infant’s head to one side.
• Normal Response: “Fencing posture”. Extension of arm and leg on the side to which face is rotated. Flexion of contralateral arm and leg.
• Clinical Nuances:
  • Visible movement may be absent; change in muscle tone is sufficient.
  • Obligatory ATNR: Infant becomes stuck in fencing posture. Always abnormal. Implies severe CNS disorder.
  • Persistent ATNR beyond 6 months strongly suggests Cerebral Palsy.

4. Rooting and Sucking Reflexes

• Elicitation (Rooting): Touch corner of lips or cheek.
• Normal Response (Rooting): Infant moves lips to suck or root in direction of stimulus.
• Elicitation (Sucking): Place clean little finger into mouth with pulp facing upwards. Touch center of lips.
• Normal Response (Sucking): Note frequency, strength, and stripping action during finger removal.
• Clinical Nuances:
  • Absent oral reflexes constitute a neonatal neurological alarm sign.
  • Essential for feeding evaluation. Poor suck indicates bulbar dysfunction or encephalopathy.

5. Parachute Reflex

• Elicitation: Hold infant’s trunk securely. Suddenly lower infant face down as if falling.
• Normal Response: Arms spontaneously extend to break the fall.
• Clinical Nuances:
  • Postural/protective reflex, not strictly a primitive disappearing reflex.
  • Prerequisite to independent walking.
  • Absence beyond 10-12 months indicates abnormal developmental reflexes and motor delay.

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Clinical Significance and Pathology

Indicators of CNS Depression

• Hypoxic-Ischemic Encephalopathy (HIE): Primitive reflexes are depressed or absent. Moderate HIE: Poor suck. Severe HIE: Unable to suck.
• General CNS Insult: Apathy, floppiness, and absent Moro/suck reflexes are critical alarm signs of early brain damage.

Indicators of Cerebral Palsy (CP)

• Persistence: Persistence of primitive reflexes (e.g., ATNR, Moro, Rooting) beyond typical disappearance age is a hallmark clinical feature of CP.
• Delayed Postural Reflexes: Absence of parachute and Landau reflexes further supports CP diagnosis.
• Prognostic Value: Persistent primitive reflexes beyond 2 years of age predict a poor neuromotor outcome and non-ambulatory status in CP.

Differential Diagnosis via Reflexes

Clinical Finding	Probable Pathology
Obligatory ATNR	Severe bilateral cortical injury / Spastic CP.
Asymmetric Moro	Peripheral nerve injury (Erb’s palsy), clavicular fracture, or structural hemiparesis.
Absent Palmar Grasp	Lower motor neuron lesion, severe hypotonia, or profound encephalopathy.
Absent Parachute	Global motor delay, severe hypotonia, evolving CP.
Persistent Rooting (>6 mo)	Diffuse cortical injury, severe intellectual disability.