What is the prognosis of spinal muscular atrophy (SMA)?

Updated: May 29, 2019
  • Author: Jeffrey Rosenfeld, MD, PhD, FAAN; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Answer

See Mortality/Morbidity for more information.

Most patients with SMA type I die before 18 months of age. In contrast, outcomes of juvenile and adult spinal muscular atrophies are difficult to define because the progression of these diseases varies widely.

Survival probabilities for types I and II and probabilities of being ambulatory for type III were derived for 445 patients. These patients were subdivided on the basis of ISMAC criteria (ie, developmental milestones and age of onset). [62]

  • SMA I: Survival probabilities at ages 2, 4, 10, and 20 years were 32%, 18%, 8%, and 0%, respectively.

  • SMA II: Survival probabilities at ages 2, 4, 10, and 20 years were 100%, 100%, 98%, and 77%, respectively.

  • SMA III: Results differed, but life expectancy of patients with SMA type III is close to that of the healthy population. Onset before age 3 years: Probabilities of being ambulatory at ages 2, 4, 10, 20, and 40 years were 98%, 94.5%, 73%, 44%, and 34%, respectively. Onset after age 3 years: Probabilities of being ambulatory at ages 2, 4, 10, 20, and 40 years were 100%, 100%, 97%, 89%, and 67%, respectively.

A recent series of 237 patients showed similar survival probabilities. [63]

Disease onset after age 2-3 months has been correlated to longer survival time in SMA type I. [64, 63] Antibiotic treatment has not prolonged survival in SMA type I. Birnkrant et al examined the role of noninvasive positive-pressure ventilation and gastrostomy in patients with SMA type I. Although these supportive measures can be effective in slowly progressive neuromuscular diseases, they did not alter survival in patients with SMA type I. [59] A later study by Lemoine et al concluded that early noninvasive respiratory intervention prolonged survival time compared with supportive care alone. [65]


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