Which physical findings are characteristic of type II 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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Patients with type II SMA have head control and can sit independently, though about 25% may lose this ability in their mid-teenage years. They have bulbar weakness resulting in difficulty with coughing, swallowing and clearing tracheal secretions. They have weak intercostal muscles, diaphragmatic breathing, and fine tremors with extended fingers or with attempted hand grips. Muscular weakness is greater in the lower extremities than in the upper extremities. Patients develop lower-extremity contractures, and about 50% lose the ability to walk by age 12 years.

Patellar reflex is absent in type II SMA. The young may demonstrate bicipital and triceps tendon reflexes. Tongue fasciculations are present, as are upper-extremity tremors. Scoliosis is universal, and most patients develop hip dislocation, either unilateral or bilateral, when younger than 10 years.

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