Spinal Muscular Atrophy



- Discussion:
    - disease of infancy and childhood, however, severity of disease is variable in its severity and progression;
    - transmitted as an autosomal recessive trait;
    - there is degeneration of the anterior horn cells of spinal cord w/ associated muscle weakness and atrophy;
    - its most severe form, Werdnig-Hoffman disease, may be noted at birth or in early infancy and usually leads to death within months;

- Clinical Findings:
    - condition presents with hypotonia, areflexia, and motor dysfunction;
    - sensation remains intact;
    - although these patients may sit, severe muscle weakness causes to joint contractures, bony abnormalities, and scoliosis;
    - most striking finding is muscle weakness;
    - patients will have minimal leg leg movement;
    - weakness progresses to upper limbs and finally to muscles of respiration;
    - death is due to respiratory compromise;
    - Kugelberg-Welander disease;
          - some children have less severe clinical picture;
          - this disorder usually manifests itself late in first decade of life;
          - it is clinically similar to muscular dystrophy, w/ slowly progressive weakness andwasting of the proximal limb muscles;
          - ability to walk is lost either late in the first decade of life or in teenage years, or pt is able to walk w/ limited ability but is never able to 
                run effectively;
          - this form may be associated with a slight rise in the level of serum "muscle" enzymes;

- EMG:
    - nerve-conduction velocities are normal in patients who have spinal muscular atrophy;
    - findings on electromyography and muscle biopsy are characteristic of neuropathic disorder, showing muscle denervation;
    - nerve-conduction velocities are normal;

- Labs:
    - in spinal muscular atrophy, creatine phosphokinase and aldolase muscle enzymes in the blood are either at normal levels or are slightly 
          elevated;

- Classification:
     - there are three forms of SMA;
     - Type I: (Werdnig Hoffmann)
            - appears between birth and 6 months of age;
            - prognosis for survival is guarded;
     - Type II:
            - appears between 6 months and 5 years;
     - Type III:
            - appears between 2 and 17 years;

- Treatment:
    - many w/ this disorder will survive well into adulthood;
    - however, other pts manifest w/ severe hypotonic & have considerable problems with eating and breathing;
           - here, treatment is limited to daily ROM exercises for joints;
           - deterioration leads to death, and orthopaedic intervention is not warranted;
           - marked hypotonia can be associated with fractures at birth;

- Deformity of the Hip:
    - valgus deformity of the proximal part of the femur, which tends to lead to subluxation of the hip;
          - unilateral dislocations are assoc w/ pelvic obliquity;
    - treatment consists of passive stretching exercises and soft-tissue releases of contracted hip muscles;
    - varus osteotomy may occassionally be needed;

- Scoliosis:
    - scoliosis is common, esp in pts who cannot walk;
    - scoliosis almost always begins in the first decade of life as a result of severe truncal weakness;
    - progression of scoliosis correlates w/ severity of the muscle weakness;
    - Bracing:
         - bracing is poorly tolerated & curves tend to progress over time;
         - for pts who do not walk, a soft anterior-opening orthosis, a wheelchair contoured back and a seating cushion, thigh & chest seat belts, 
                & head rest, are helpful;

- Operative Correction of Scioliosis:
    - surgery may prevent progression of curve & may improve sitting comfort;
    - indications:
          - patients who are > ten years old;
          - flexible curve of > 40 degrees;
          - forced vital capacity of > 40 per cent;
    - patients w/ SMA may use diaphragm and anterior abdominal muscles for respiration and hence,  anterior approaches are contraindicated;
    - posterior arthrodesis: options:
           - two Luque rods
           - Harrington distraction rod on concave side & Luque rod on convex sides;
           - arthrodesis to the sacrum;
           - bone may be too weak for sublaminar wires



Spinal deformities in patients with spinal muscle atrophy: a review of 36 patients.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, May 24, 2012 3:45 pm