Which physical findings are characteristic of spinal muscular atrophy (SMA) type I - acute infantile or Werdnig-Hoffman disease?

Updated: May 29, 2019
  • Author: Jeffrey Rosenfeld, MD, PhD, FAAN; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Diffuse muscle weakness and hypotonia can be demonstrated with a variety of bedside maneuvers, including the traction response, vertical suspension, and horizontal suspension tests.

In general, infants with SMA type I cannot hold their heads up when pulled to the sitting position, and they will slip through the examiner's hands when held vertically. They lay limp in the physician's hand when held under the abdomen and facing down.

Weakness is greater in proximal than distal muscles and may mimic muscle disease (myopathy).

Findings on sensory examination are normal. Deep tendon reflexes are absent, as are long-tract signs and sphincteral abnormalities.

Arthrogryposis, or deformities of the limbs and joints at birth, can be observed and results from in utero hypotonia. Skeletal deformities (scoliosis) may be present.

In the infant or newborn, fasciculations are often restricted to the tongue, but tongue fasciculations can be difficult to distinguish from normal random movements unless atrophy is also present.

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