The condition typically affects young children. Presents with progressive proximal predominant muscle wasting and weakness of varying severity. Lower extremities can have greater involvement.
SMA can be classified into four types 3:
- type 1: Werndig-Hoffman disease: most severe and most common form (onset before six months)
- type 2: intermediate (onset between six and 12 months)
- type 3: Kugelberg-Welander disease: juvenile form (onset after 12 months)
- type 4: adult onset
Inherited as an autosomal recessive form which mutations to SMN1 (survival motor neurone 1) gene on chromosome 5 3.
Shows wasting of musculature. Mild types tend to demonstrate fatty infiltration of muscular bundles with increased intramuscular fat planes 1. Intermediate forms may show ragged atrophy of muscles while the severe forms often show gross atrophy.
Treatment and prognosis
Treatment is mainly supportive. Carries a poor prognosis. Overall length of survival depends on type.
- 1. Chan WP, Liu GC. MR imaging of primary skeletal muscle diseases in children. AJR Am J Roentgenol. 2002;179 (4): 989-97. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Murphy WA, Totty WG, Carroll JE. MRI of normal and pathologic skeletal muscle. AJR Am J Roentgenol. 1986;146 (3): 565-74. AJR Am J Roentgenol (abstract) - Pubmed citation