Spinal muscular atrophy
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Synopsis

- Type 1 (Werdnig-Hoffman disease) is characterized by symptom onset before 6 months of age. These patients are profoundly hypotonic, have significant respiratory and nutritional difficulties, and never achieve sitting without support. Historically, this type is fatal within 2 years.
- Type 2 is characterized by symptom onset between 6-12 months, weakness, tremors, and respiratory and nutritional problems. These patients are able to achieve sitting but never walk independently.
- Type 3 is the least severe type and is characterized by symptom onset after 1 year of age. Many live into adulthood and achieve walking prior to losing this ability in late childhood or early adulthood. The weakness in type 3 is variable. These patients typically do not have respiratory or nutritional difficulties.
Codes
ICD10CM:G12.9 – Spinal muscular atrophy, unspecified
SNOMEDCT:
5262007 – Spinal muscular atrophy
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Diagnostic Pearls
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Differential Diagnosis & Pitfalls
Differential diagnosis varies by SMA type.Type 1:
- Spinal muscular atrophy with respiratory distress (SMARD1)
- X-linked infantile spinal muscular atrophy
- Congenital myopathy
- Toxic / metabolic etiologies of hypotonia
- Congenital myasthenic syndrome
- Congenital myotonic dystrophy
- Arthrogryposis multiplex congenita
- Prader-Willi syndrome
- Lysosomal storage diseases (eg, Pompe disease)
- Muscular dystrophies
- Non-5q forms of SMA
- Lysosomal storage diseases
- Guillain-Barré syndrome (distinguishable by subacute-acute onset and pattern of presenting weakness)
- Congenital myopathies
- Infantile botulism
- Spinal-dural arteriovenous malformation / fistula
- Poliomyelitis
- Postpolio syndrome
- West Nile virus
- Syringomyelia
- Facioscapulohumeral muscular dystrophy
- Amyotrophic lateral sclerosis
- Kennedy disease (spinobulbar muscular atrophy)
- Chronic inflammatory demyelinating polyneuropathy
- Myasthenia
- Polymyositis
- Multifocal motor neuropathy
- Lead toxicity
- Dapsone toxicity
Best Tests
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Management Pearls
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Therapy
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References
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Last Reviewed:11/01/2018
Last Updated:01/24/2022
Last Updated:01/24/2022