neurologic disorders
Spinal Muscular Atrophies (SMAs)
Diagnosis of SMAs
Electrodiagnostic testing Genetic testing A diagnosis of spinal muscular atrophy should be suspected in patients with unexplained muscle wasting and flaccid weakness, particularly in infants and children. Electromyography (EMG) and nerve conduction studies should be done; muscles innervated by cranial nerves should be included. Conduction is normal, but affected muscles, which are often clinically unaffected, are denervated. Definitive diagnosis is by genetic testing, which detects the causative mutation in about 95% of patients. Muscle biopsy is done occasionally to exclude treatable causes and to determine whether the cause is fatal. Serum enzymes (eg, creatine kinase, aldolase) may be slightly increased. Amniocentesis, done if family history is positive, is often diagnostic. 