Spinal muscular atrophy

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  • Degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem

Type 1

  • Autosomal Recessive
  • Also known as infantile spinal muscular atrophy or Werdnig-Hoffmann disease
  • The most common and severe type of SMA

Clinical Features

Type 1

  • Severe symmetric flaccid paralysis: unable to sit unsupported
  • Upper cranial nerves spared: alert expression and normal eye movements
  • Weakness of the bulbar muscles: weak cry, poor suck and swallow reflexes, pooling of secretions, aspiration, and fasciculations of the tongue
  • Respiratory failure: intercostal muscles typically more affected than the diaphragm, resulting in paradoxical breathing (inspiratory efforts cause the rib cage to move inward and the abdomen to move outward) and the development of a characteristic bell-shaped chest deformity

Type 2,3,4

  • SMA 2 (intermediate form) and SMA 3 (mild form; Kugelberg-Welander disease) have a later onset and a less severe course. SMA 2 presents between 3 and 15 months of age, whereas SMA 3, the least severe, typically presents with signs of weakness at or after one year of age and progresses to a chronic course. Adult onset of SMA (type 4) usually presents in the second or third decade of life and is otherwise similar to SMA type 3.

Differential Diagnosis

Hypotonic neonate

  • Arthrogryposis multiplex congenita
  • X-linked infantile spinal muscular atrophy
  • Spinal muscular atrophy with respiratory distress type 1
  • Congenital myasthenic syndromes
  • Congenital myopathies
  • Hypoxic-ischemic myelopathy
  • Lysosomal acid maltase deficiency
  • Prader-Willi syndrome
  • Traumatic myelopathy
  • Zellweger syndrome



Type 1

  • Supportive and directed at providing nutrition and respiratory assistance as needed, and treating or preventing complications of weakness. Physical therapy may be helpful. Spinal bracing can be used to delay the development of progressive scoliosis that is caused by muscle weakness, but may reduce expiratory tidal volume, and thus it should be used cautiously.
  • Chest physiotherapy with postural drainage, and manual cough assistance and/or use of a mechanical insufflation/exsufflation device.


See Also

External Links