Which clinical history findings are characteristic of spinal muscle atrophy (SMA)?

Updated: May 04, 2020
  • Author: Ashish S Ranade, MBBS, MS, MRCS; Chief Editor: Jeffrey A Goldstein, MD  more...
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Spinal muscle atrophy (SMA; also known as spinal muscular atrophy) is a single-gene disorder with a spectrum of clinical presentation. The clinical presentation includes a wide range of phenotypes that are classified into groups on the basis of age of onset and maximum level of motor function achieved, but hypotonia and/or muscle weakness and atrophy are common signs and symptoms.

With type I SMA, most mothers report abnormal inactivity of the fetus in the latter stages of pregnancy. Babies with type I SMA face many physical challenges, including trouble breathing, coughing and swallowing.Patients with type I SMA are unable to roll over or sit. Progressive clinical deterioration occurs. Death usually occurs from respiratory failure and its complications by age 2 years.

Patients with type II SMA have normal development for the first 4-6 months of life. They are able to sit independently but are never able to walk independently. They require a wheelchair for locomotion. They have a longer life span than patients with type I SMA. Some patients with type II SMA live into the fifth decade of life, with more than 70% still living at 25 years of age.

In patients with type III SMA, the presenting complaint is difficulty climbing stairs or getting up from the floor (due to hip extensor weakness). Individuals affected by SMA type III initially are able to walk independently, but as they grow, their mobility is increasingly limited, and they eventually may need to use a wheelchair. The lifespan is nearly normal. [24]

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