Alternate Names: Werdnig-Hoffmann disease

Causes and Risks:

Spinal muscular atrophy is the second leading cause of neuromuscular disease. (Duchenne muscular dystrophy is number one.) Spinal muscular atrophy is inherited as an autosomal recessive trait and has an incidence of approximately 4 per 100,000 people.

In its most severe form (SMA I), infants are born floppy with weak, thin muscles, and feeding and breathing problems. Their lifespan seldom exceeds more than 2 to 3 years. Infants with SMA type II have less severe symptoms during early infancy, but they become progressively weaker with time. Survival time with type II is longer. SMA type III is the mildest form of the disease and symptoms may not appear until the second year of life. Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness is progressive and will eventually become profound, but children may survive into early adulthood.

Rarely, SMA may present in adulthood and is usually a milder form of the disease. It may be inherited in an autosomal dominant or autosomal recessive manner.

Prevention: Genetic counseling is recommended for prospective parents with a family history of spinal muscular atrophy.

Symptoms:

• Family history of spinal muscular atrophy
• Floppy infant
• Very weak infant
• Little spontaneous movement (infant)
• Lack of head control (infant)
• Feeding difficulty (infant)
• Breathing difficulty (infant)
• Progressive weakness (older infant to toddler)
• Nasal speech (child)
• Worsening posture (child)
• Frequent increasingly severe respiratory infections

Signs and Tests:

• A family history of neuromuscular disease
• Absent deep tendon reflexes
• Flaccid muscles
• Muscle fasciculation
• Fasciculation of tongue muscle
• Elevated CPK levels

• Muscle biopsy
• Electromyography

Treatment: There is no treatment for the progressive weakness caused by the disease. Supportive care is important. Attention must be paid to the respiratory system as affected people have difficulty clearing secretions and respiratory complications are common. Physiotherapy is important to prevent contractures and scoliosis. Bracing may be necessary.

Prognosis: The most severe form of spinal muscular atrophy is fatal early on. The less severe form is compatible with a longer lifespan. However, progressive weakness and debility are present in all forms.

Complications:

• Contractures
• Scoliosis
• Respiratory infections
• Aspiration

Call your health care provider if your child appears weak, has difficulty feeding, or develops any other of the symptoms of spinal muscular atrophy. Breathing difficulty can rapidly become an emergency condition.