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Electrodiagnostic testing is an essential component in evaluating patients with suspected myopathy. There are different types of myopathies, including hereditary and acquired forms, and many specialists have involvement in the care of patients with muscle disorders, including neurologists, physiatrists, rheumatologists, pulmonologists, cardiologists, orthopedic surgeons, and others. This activity outlines the pathophysiological basis for electrodiagnostic testing in muscle disorders, explains the clinical significance of the test, and highlights the importance of the team approach in evaluating patients with myopathies. Objectives: Identify am the pathophysiological basis for electrodiagnostic testing in muscle disorders. Assess the typical electrodiagnostic findings in myopathies. Evaluate patterns and topographical distribution of abnormal electrodiagnostic signs in different types of myopathies. Collaborate with the interprofessional team to employ electrodiagnostic testing to diagnose myopathy patients. Access free multiple choice questions on this topic.

Electrodiagnostic testing is the core diagnostic modality for patients with a suspected myopathy; it comprises nerve conduction studies (NCS) and electromyography (EMG). Despite recent advances in molecular genetics and significant improvement in imaging quality, it is still a pertinent part of the diagnostic process in most patients. Electrodiagnostic studies are considered an extension of the physical examination and are most useful in the workup of a patient with a suspected myopathy.[1] NCS usually precedes needle EMG and provides valuable information about the function of sensory and motor nerve fibers. NCS is normal in most patients with muscle disorders and assists in excluding disease mimickers. In some cases, specialized tests, such as repetitive nerve stimulation, can be employed to evaluate neuromuscular junction disorders as another cause of pure motor weakness. The performance of EMG for myopathy evaluation involves placing a needle-recording electrode inside the muscle and analyzing electrical potentials at rest and with muscle activation. The selection of muscles for electrodiagnostic examination depends on the clinical scenario and technical limitations. Testing clinically weak muscles increases the yield of the test. Most myopathies affect proximal muscles; therefore, limb-girdle and paraspinal muscles are usually tested. In certain myopathies, distal muscles are preferentially involved (myofibrillar myopathies, distal muscular dystrophies). In such cases, this can lead not only to abnormal EMG but also to abnormal motor nerve conductions due to muscle atrophy.[2] Electrodiagnostic studies not only allow confirmation of myopathy diagnosis and assist in identifying etiology but can also be used to select a suitable site for muscle biopsy or to direct further genetic testing.[3][4]

Electrodiagnostic studies are safe and generally well tolerated by patients. Iatrogenic side effects are very rare. Transdermal electrical stimulation produces a theoretical risk for electrical complications in nerve conduction studies. Needle EMG carries the potential complications of any needle insertion, including infection, hemorrhage, tissue injury, and pneumothorax. Electrical complications. The electrical current that stimulates the nerve may pose a risk for some patients. Modern equipment has built-in electrical insulation to prevent potential electric injury during an electrodiagnostic study. Maintaining equipment regularly and using ground electrodes and grounded outlets is essential. Nerve conduction studies are safe in patients with peripheral and central intravenous lines, modern implantable pacemakers, and defibrillators with bipolar leads.[12] Studies performed in the ICU settings require more caution, as the presence of external wires and other electrical equipment makes patients sensitive to microcurrents. Electrodiagnostic studies should be avoided in patients with external temporary pacemakers. Pneumothorax. The most dangerous iatrogenic complication of needle EMG is pneumothorax. Even though this complication is rare, examining particular muscles - serratus anterior, diaphragm, thoracic, lower cervical paraspinal muscles, rhomboid, and suprascapular muscles - carries increased risk. The best strategy is to avoid sampling these muscles on routine studies.[13] In situations when testing of high-risk muscles is necessary, ultrasound guidance of needle placement can be used.[12] Hemorrhage. Bleeding complications during needle EMG are extremely rare.[8][14][15] Studies of muscles using magnetic resonance imaging and ultrasound after needle EMG showed that the risk of clinically symptomatic hematoma is very low, even in patients on anticoagulation or antiplatelet therapy.[14][15][14] It is recommended that anticoagulation and antiplatelet medications should not be held before needle EMG.[12] Special strategies to reduce the risk of hemorrhage include using the smallest gauge needle, limiting the number of needle passes, avoiding deep muscles that cannot be externally compressed, and not testing muscles located near large vessels.[5]

Hemorrhage. Bleeding complications during needle EMG are extremely rare.[8][14][15] Studies of muscles using magnetic resonance imaging and ultrasound after needle EMG showed that the risk of clinically symptomatic hematoma is very low, even in patients on anticoagulation or antiplatelet therapy.[14][15][14] It is recommended that anticoagulation and antiplatelet medications should not be held before needle EMG.[12] Special strategies to reduce the risk of hemorrhage include using the smallest gauge needle, limiting the number of needle passes, avoiding deep muscles that cannot be externally compressed, and not testing muscles located near large vessels.[5] Infections. Since the use of disposable needles, this potential complication has not been reported. Clean technique and reasonable caution are recommended for the procedure.  Infected areas of the skin should be avoided.[16]

Electrodiagnostic testing is a valuable technique for evaluating a suspected myopathy patient. The standard test usually includes nerve conduction studies and needle EMG examination. The care of patients with disorders of muscle often involves different specialties, including neurologists, rheumatologists, orthopedic surgeons, primary care providers, physical and occupational therapists, speech pathologists, cardiologists, and others. The traditional approach to diagnosis has evolved in the era of molecular genetics and neuroimaging breakthroughs. It requires a tailored approach to each patient where an electrodiagnostic study is required. Enhancing knowledge about electrodiagnostic studies and their role in diagnosing neuromuscular disorders among different healthcare providers improves the appropriateness of referrals and yield of the tests.[26] Proper patient selection and appropriate techniques can guide further diagnostic investigations, including genetic testing, muscle biopsy, and treatment strategies. Overall, electrodiagnostic testing is safe and well-tolerated by most patients. However, sometimes, it can cause sufficient patient discomfort, leading to aborted studies or inconclusive results. It has been shown that a lack of information or incorrect information about the test is associated with higher anticipated pain and test failure in some patients.[12][26][12] Studies also showed that needle EMG is less painful than expected, and patients who underwent electrodiagnostic studies are willing to repeat the test if necessary.[12][27] Anticoagulation is only a relative contraindication for needle EMG, usually requiring careful planning and approach, but studies have shown the procedure to be safe. Improving communications and expanding knowledge of the electrodiagnostic evaluation's principles, indications, and limitations, as well as its role in the patient workup and further management, help make timely clinical decisions and improve treatment outcomes.