The differential diagnosis for adult-onset SMA includes amyotrophic lateral sclerosis and Kennedy disease, and other disorders of the peripheral nervous system including myopathy (dystrophinopathies, limb girdle muscular dystrophy, metabolic myopathies, or inflammatory myopathies), neuropathy (inflammatory neuropathies), neuromuscular junction disorders (myasthenia gravis or congenital myasthenic syndromes), and other motor neuron disorders (non-5q form of SMA or late-onset hexosaminidase A deficiency).
Before molecular testing became available, diagnostic studies to demonstrate the presence of denervation, such as electrodiagnostic studies and muscle biopsy, were important tools for evaluating suspected SMA. Typically, electrodiagnosis is now reserved only for evaluation of atypical patients or patients who are negative for both SMN1 deletion and SMN1 mutation testing. Muscle biopsy is no longer indicated because electrodiagnosis can more easily demonstrate features of denervation.
Learn more about the workup for SMA.
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Cite this: Stephen L. Nelson. Fast Five Quiz: Spinal Muscular Atrophy in Adults - Medscape - Feb 01, 2021.