Asymmetric Moro's Reflex at birth is indicative of?

HPSSC Staff Nurse - 2021

Pediatric Nursing

Medium

Appeared in: HPSSC Staff Nurse - 2021

Explanation

The Moro reflex is a normal neonatal reflex where the infant startles, extends their arms, and then brings them back to the midline symmetrically.
An 'asymmetric' response means one side of the body does not respond in the same way as the other, pointing to a localized or peripheral problem rather than a central brain issue.
Erb's palsy is an injury to the brachial plexus nerves (C5-C6) that control the arm, typically from a difficult delivery. This nerve damage causes weakness or paralysis in the affected arm, leading to its failure to move during the Moro reflex.
Other causes for an asymmetric reflex can include a fracture of the clavicle or humerus on the affected side, which would also cause the infant to not move the painful limb.

Option A: Hypoxic ischemic encephalopathy (HIE) is a global brain injury. It typically causes bilateral (symmetrical) signs, such as a completely absent, weak, or hyperactive Moro reflex on both sides, not an asymmetric one.
Option B: Like HIE, significant 'brain damage' is a central nervous system issue that usually results in generalized, bilateral reflex changes. An isolated asymmetric finding points away from a diffuse brain injury.
Option D: Kernicterus (bilirubin encephalopathy) presents with generalized symptoms affecting the whole body, such as lethargy, a high-pitched cry, and abnormal muscle tone (opisthotonos). It does not cause an isolated, asymmetric reflex.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of neonatal reflexes, specifically the Moro reflex as background academic context rather than a clinical decision trigger.
A nurse performing a newborn assessment is often the first to identify an asymmetric Moro reflex. Prompt identification and reporting are crucial for early diagnosis and intervention, which can significantly improve long-term function.
When an asymmetric reflex is noted, the nurse should perform a careful examination of the affected limb for other signs of injury, such as decreased movement, abnormal positioning, or crepitus (a crackling feeling) over the clavicle, which might suggest a fracture.
What if? If the infant had an asymmetric Moro reflex but also had palpable crepitus and pain over the collarbone, a fractured clavicle would be the primary suspicion over Erb's palsy, although both can occur together.

How to Approach the Question

First, understand the keyword 'asymmetric'. This means 'uneven' or 'one-sided'. In reflexes, it points to a problem on one side of the body.
Next, differentiate between central and peripheral causes. Central problems (in the brain) usually cause symmetric, bilateral effects. Peripheral problems (in a limb or nerve) cause asymmetric, unilateral effects.
Evaluate the options. 'Hypoxic ischemic encephalopathy', 'Brain damage', and 'Kernicterus' are all central problems affecting the brain. They would likely cause bilateral changes.
'Erb's palsy' is a peripheral nerve injury affecting only one arm. This perfectly matches the 'asymmetric' finding.
Conclude that the localized, peripheral nature of Erb's palsy makes it the most logical cause for a one-sided reflex abnormality.

Concept Tested & Keywords

Concept Tested: Interpretation of neonatal reflexes, specifically the Moro reflex.
Stem keywords: Asymmetric Moro's Reflex, at birth, indicative of
Lead-in keywords: indicative of
Negative lead-in flag: false

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E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 1061-1063