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Pediatrics – Hypotonic Infant: By Wendy Stewart M.D.

Pediatrics – Hypotonic Infant: By Wendy Stewart M.D.

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Pediatrics – Hypotonic Infant
Whiteboard Animation Transcript
with Wendy Stewart, MD, PhD

In infants, hypotonia is seen in both upper and lower motor neuron lesions. A neurologic history and examination will allow you to localize the level of the problem.


A history of birth depression, seizures, or encephalopathy all indicate a central cause.

Breech presentation may result in transection of the cord. This type of history, together with global developmental delay or early handedness, all point to an upper motor neuron cause for the hypotonia.

Weakness with normal cognition indicates a problem in the peripheral nervous system.

Look for associated problems, such as multiorgan involvement, feeding, or breathing issues that may point to a particular nervous system level and diagnosis.

A family history of similar difficulties may provide a clue to diagnosis.


On examination, the presence of dysmorphic features may identify a specific syndrome.

Fisting beyond the first few months of life is abnormal and associated with central causes of hypotonia.

In vertical suspension, scissoring indicates abnormal motor signals to the legs.

A sensory level with bladder sphincter abnormalities points to spinal cord involvement.

Depressed or absent tendon reflexes are indicative of a peripheral cause due to disruption of the monosynaptic reflex arc.

Fasciculations are spontaneous muscle contractions and are best seen in the tongue. They indicate a problem with the motor unit.

A lack of movement when trying to elicit primitive reflexes indicates weakness involving the peripheral nervous system.


In summary, hypotonia in an infant can arise from lesions anywhere along the neuroaxis. Make sure you look for all the clues to localise where the lesion is.

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