Physical Medicine and Rehabilitation Clinics of North America
Diagnosis and Clinical Management of Spinal Muscular Atrophy
Section snippets
Classification, patterns of severity, and survival
SMA is generally divided into clinical subtypes using age of onset, achieved developmental milestones, ability to achieve independent sitting, standing, walking, and survival as classification criteria. The International Consortium on SMA attempted to standardize the classification of SMA to provide a rational basis for linkage studies and therapeutic trials (Table 1) [9], [10]. SMA type I (SMA I) (Werdnig-Hoffmann, severe form) was defined by the consortium as follows: onset from birth to 6
Genetics of autosomal recessive, predominantly proximal spinal muscular atrophy
The carrier frequency for SMA in the general population is estimated at about 1 in 40 to 50 individuals [19]. Autosomal recessive inheritance has long been documented in proximal SMA with childhood onset. In 1990, all three forms of SMA were mapped to chromosomal region 5q13, indicating that allelic variants of the same disease locus account for the clinical heterogeneity [20], [21]. During the past 2 decades, tremendous advances have been made in our understanding of the genetic basis for SMA
Spinal muscular atrophy I
In many instances, mothers of SMA I cases report experiencing reduced fetal movements. Most cases present within the first 2 months. Weak suck, dysphagia, labored breathing during feeding, aspiration of food or secretions, and a weak cry are also frequently noted. Examination shows generalized hypotonia and symmetric weakness involving the lower extremities earlier and to a greater extent than the upper extremities. Proximal muscles are weaker than distal muscles. In the supine position, the
Serum laboratory studies
Creatine kinase levels have been found to be normal to elevated two to four times in SMA I and II [35]. SMA III patients can also have normal to slightly elevated creatine kinase values [37]. A serum creatine kinase level greater than 10 times the upper limit of normal is generally an exclusionary criterion for SMA [10] and workup for other disorders such as inflammatory or dystrophic myopathies should be pursued. Functional status and disease progression did not correlate with creatine kinase
Diagnostic evaluations
If the diagnosis of SMA is strongly suspected, a SMN gene deletion test can be done to confirm the diagnosis. At this time, a genetic test for SMA is commercially available. The test is based on the homozygous absence of SMN1 exon 7, with or without a concomitant exon 8 deletion. The sensitivity and specificity of the gene deletion test are excellent and approach 95% and 100%, respectively. The test results are usually available in several weeks. The copy number of the SMN2 gene is also
Functional status evaluation in spinal muscular atrophy
Functional status evaluation, including gross motor milestone acquisition, independence in mobility, hand function, activities of daily living, and timed motor performance, have all been shown to be correlated with strength in SMA II and SMA III [14], [53], [54]. Patients have been documented to lose motor function over time without loss in absolute muscle strength [14], [115]. Especially in severely weak patients who have SMA, traditional strength measurements are not as useful or clinically
Psychosocial evaluation
Normal intellectual function has been documented among SMA patients [17], [121]. In regards to comorbid behavioral problems, a recent study found that 12.5% of SMA patients fulfilled the criteria for a Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) diagnosis, with separation anxiety disorder being the most common diagnosis [122]. The investigators concluded that children and adolescents who have SMA are characterized by a low psychiatric comorbidity and are not
Summary
Although many advances have been made regarding our understanding of SMA, unfortunately, no cure is yet available. However, neuromuscular medicine specialists have an important role in the care of patients who have SMA to maximize their functional capacities, prolong or maintain independent locomotion, prevent physical deformity and medical complications, and improve the quality of life. Many complex medical issues are associated with SMA that can be managed effectively by medical providers.
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2010, Sleep Medicine ClinicsCitation Excerpt :All patients achieve independent walking ability. Swallowing dysfunction, cough, and nocturnal hypoventilation are less common.79 For SMA patients, NPPV can be provided as routine therapy or as a palliative tool.
This work was supported by Grant H133B03111805 from the National Institute of Disability and Rehabilitation Research (NIDRR).