What is spinal muscle atrophy (SMA)?

Updated: May 04, 2020
  • Author: Ashish S Ranade, MBBS, MS, MRCS; Chief Editor: Jeffrey A Goldstein, MD  more...
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Spinal muscle atrophy (SMA; also known as spinal muscular atrophy) is a rare debilitating autosomal recessive hereditary disease characterized by progressive hypotonia and muscular weakness. The characteristic muscle weakness occurs because of a progressive degeneration of the alpha motor neuron from anterior horn cells in the spinal cord. The weakness is more severe in the proximal musculature than in the distal segments.

In certain patients, the motor neurons of cranial nerves (especially cranial nerves V-XII) can also be involved. Sensation, which originates from the posterior horn cells of the spinal cord, is spared, as is intelligence. Several muscles are spared, including the diaphragm, the involuntary muscles of the gastrointestinal system, the heart, and the sphincters. [1, 2, 3, 4]

In 1890, Werdnig described for the first time the classic infantile form of SMA. [5]  Many years later, in 1956, Kugelberg and Welander described the less severe form of SMA. [6]  Werdnig, in 1890, [5]  and Hoffman, in 1891, [7]  reported cases of muscular dystrophy occurring in infants that were otherwise similar to cases of muscular dystrophy found in older children and adults (eg, Duchenne muscular dystrophy).

SMA is the most common diagnosis in girls with progressive weakness. It is one of the most common genetic causes of death in children.

No two children with SMA will be exactly the same. Accordingly, treatment and care plans for each family should be tailored to meet specific individual needs. Ideally, a team-based comprehensive supportive approach to care optimizes outcomes in these children. The team should consist of a neurologist, a pulmonologist/intensivist, an orthopedic surgeon, a nutritionist, genetic counselors, social workers, an orthoptist, and occupational and physical therapists.

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