Along with electromyography and nerve conduction velocities (NCV) test, a muscle or nerve biopsy can be used to diagnose spinal muscular atrophy if molecular genetic testing of SMN1 does not identify mutations.
During a diagnostic muscle biopsy surgical procedure, an incision approximately 3 inches long is made and a small section of muscle from the upper thigh is removed. The biopsy is used to check if the muscles are degenerating or have characteristics unique to SMA, such as group atrophy of type 1 and type 2 muscle fibers instead of the normal checkerboard pattern seen in healthy muscles.
SMA type 1 muscle biopsies usually reveal a characteristic pattern of perinatal denervation (loss of nerve supply), which is unlike that of mature muscle. Groups of giant muscular fibers are mixed with fascicles (bundles) of severely atrophic fibers. SMA types 2 and 3 muscle biopsies have a pattern more similar to an adult muscle that has undergone many cycles of denervation and reinnervation (restoration of nerve supply).
Muscle Biopsies: What To Expect?
The patient can undergo the procedure as an outpatient because it typically does not involve general anesthetic.
A local anesthetic is used to numb the area where the biopsy is performed. After the procedure, the incision is cared for and dressed. Some local pain and discomfort can be felt on the skin and muscle involved in the biopsy, but physicians can help relieve the pain by prescribing medication to be taken as directed.
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