SMA is diagnosed primarily through a blood test, which looks for the presence or absence of the SMN1 gene, in conjunction with a suggestive history and physical examination.
SMA is often diagnosed on a clinical basis by how the child appears physically. The diagnosis may be suspected when children are noted to be weak or to have a delay in their developmental milestones, such as holding their head up, rolling over, sitting independently, standing, or walking later than would be expected. After a thorough medical history is reviewed and a physical exam is performed, a primary care provider may order genetic testing through a blood sample, or a child may be referred to a neurologist who will also perform an examination and then order genetic testing (again through a blood sample) to confirm the diagnosis. Occasionally, an electromyography (EMG) or a muscle biopsy may be performed, or a creatine kinase (CK) level ordered. If it’s necessary, EMG is a test that measures the electrical activity of muscle. Sometimes this test is performed to help distinguish SMA from other disorders of nerve or muscle that may look similar to SMA. Small recording electrodes (needles) are inserted into the individual’s muscles, usually the arms and thighs, while an electrical pattern is observed and recorded. A muscle biopsy is a procedure in which a small sample of muscle is obtained in an operating room for further examination in a laboratory, again to help distinguish SMA from other muscle diseases. Results from an EMG or a muscle biopsy may be useful in instances when the diagnosis of SMA remains uncertain. A CK level is measured through a blood sample and an elevated level indicates muscle disease. While this is not usually found in SMA, it may be helpful to distinguish SMA from other forms of muscle disease.
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