Fast Five Quiz: Can You Diagnose the Different Types of Spinal Muscular Atrophy?

Stephen L. Nelson, Jr, MD, PhD

Disclosures

December 06, 2018

Genetic testing is the most efficient and reliable method to test for SMA. Homozygous SMN1 gene deletion is 100% specific and 95% sensitive for SMA.

For patients in whom SMA is still suspected despite the absence of homozygous deletion of SMN1, further sequencing of any present SMN1 copies is recommended. If genetic testing proves unrewarding, further laboratory evaluation is required.

Prenatal ultrasound for SMA does not usually reveal significant abnormalities. Chorionic villi sampling and amniocentesis are relatively accurate in detecting SMA; however, clinicians should be wary of diagnosis through these methods alone when any atypical features are present. Because CSF analyses are normal in patients with SMA, it is not an appropriate diagnostic test for the SMA. Radiography can be valuable if genetic testing is unrewarding, but findings may be nonspecific to SMA.

Differential diagnoses to consider include:

  • Congenital muscular dystrophy

  • Congenital myopathies

  • Primary lateral sclerosis

  • Amyotrophic lateral sclerosis

  • Disorders of carbohydrate metabolism

  • Myasthenia gravis

For more on diagnostic testing for SMA, read here.

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