Encyclopedia Home / S / Spinal muscular atrophy

Spinal muscular atrophy

  • Alternative Names

    Werdnig-Hoffmann disease


    Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems. With SMA type III, symptoms may not appear until the second year of life.

    Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness gets worse over time and will eventually become severe.

    Symptoms in an infant:

    • Breathing difficulty
    • Feeding difficulty
    • Floppy infant (poor muscle tone)
    • Lack of head control
    • Little spontaneous movement
    • Progressive weakness (older infant to toddler)
    • Very weak infant

    Symptoms in a child:

    • Frequent, increasingly severe respiratory infections
    • Nasal speech
    • Worsening posture

    Signs and tests

    The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:

    • A family history of neuromuscular disease
    • Floppy (flaccid) muscles
    • No deep tendon reflexes
    • Twitches (muscle fasciculation) of tongue muscle


    • CPK levels
    • DNA testing to confirm diagnosis
    • Electromyography
    • MRI of the spine
    • Muscle biopsy