Which clinical history findings are characteristic of spinal muscular atrophy (SMA) type II - chronic infantile form?

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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This is the most common form of spinal muscular atrophy, and some experts believe that SMA type II may overlap types I and III.

Most children present between the ages of 6 and 18 months.

The most common manifestation that parents and physicians note is developmental motor delay. Infants with SMA type II often have difficulties with sitting independently or failure to stand by 1 year of age.

An unusual feature of the disease is a postural tremor affecting the fingers. This is thought to be related to fasciculations in the skeletal muscles.

Pseudohypertrophy of the gastrocnemius muscle, musculoskeletal deformities, and respiratory failure can occur.

The lifespan of patients with SMA type II varies from 2 years to the third decade of life. Respiratory infections account for most deaths.

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