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Key Features

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  • Classic maneuvers to evaluate a floppy infant include checking vertical suspension, horizontal suspension, and traction response

  • Correct interpretation of neurologic findings in a hypotonic infant depends on a thorough knowledge of normal childhood development

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Clinical Findings

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  • In vertical suspension, the hypotonic infant will slip through the examiner's hands when held under the armpits

  • Horizontal suspension (ie, supporting the infant with a hand under the chest)

    • Normally results in the infant's holding its head slightly up (45 degrees or less), the back straight or nearly so, the arms flexed at the elbows and slightly abducted, and the knees partly flexed

    • The "floppy" infant droops over the hand like an inverted U

  • Traction response

    • Normal newborn attempts to keep the head in the same plane as the body when pulled up from supine to sitting by the hands

    • Marked head lag is characteristic of the floppy infant

  • Hyperextensibility of the joints is not a dependable criterion

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Diagnosis

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  • A general rule for laboratory testing is to localize the etiology of the hypotonia

  • If a lower motor neuron etiology is suspected, appropriate first tier testing may include

    • Serum creatine kinase

    • Electromyogram/nerve conduction studies

    • Muscle biopsy

  • Many neuromuscular disorders may be diagnosed by clinical findings alone, as is often the case with spinal muscular atrophy and congenital myotonic dystrophy, and in those cases, genetic testing is warranted

  • If the hypotonic is accompanied by language or cognitive delay, a CNS or genetic disorder is most likely, and MRI of the brain may be the most useful diagnostic test

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Treatment

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  • Supportive

  • Physical and occupational therapy can facilitate some progress

  • Accompanying seizures and other systemic manifestations should be controlled to optimize development

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