Last updated: November 8, 2014
Synonyms: EMG, electrodiagnostic studies
CPT- Code: Needle electromyography 1 extremity 95860; 2 extremities 95861; 3 extremities 95863; 4 extremities 95864
Description: EMG is a diagnostic test used to evaluate patients with suspected muscle disease. EMG is often performed in conjunction with nerve conduction testing.
Method: This test assesses the electrical activity and physiologic function of muscle by placing needle electrodes into selected muscle groups. EMG is usually obtained in conjunction with nerve conduction tests to assess the neural component to the patients complaint. The procedure does not use external electrical stimulation. Muscle action potentials are produced as waveforms (recorded on an oscilloscope), with specific patterns corresponding to various types of pathologic processes in muscle tissues. EMG is generally performed by specially trained individuals (i.e., neurologist or physiatrist). Because the test is relatively nonspecific, it is important that the clinician provide as much clinical information as possible along with the EMG request to aid in interpretation of the findings.
Normal in: EMG is not useful or diagnostic in fibromyalgia, polymyalgia rheumatica, restless legs, and muscle cramps.
Abnormal in: For patients with inflammatory muscle disorders such as polymyositis or dermatomyositis, characteristic EMG findings include (a) generally increased insertional activity and spontaneous discharges (indicating muscle irritability); (b) decreased amplitude and duration of motor unit action potentials; and (c) an increased number of polyphasic potentials. Although none of these findings is necessarily specific for a given myopathic diagnosis, other potential causes of muscle weakness, such as neuropathies, can often be excluded from further consideration.
Indications: EMG is primarily used to distinguish between weakness caused by disorders of muscle (e.g., muscular dystrophy, inflammatory myositis), peripheral motor neuron (e.g., peripheral neuropathy, radiculopathy), or neuromuscular junction (e.g., myasthenia gravis, Eaton-Lambert syndrome).
Contraindications: EMG is contraindicated with thrombocytopenia, severe coagulopathy, and anticoagulant use.
Confounding Factors: If a muscle biopsy is contemplated, the EMG needles should be placed on the side opposite the biopsy site because low-grade inflammatory infiltrates may result from needle insertion. EMG itself may also result in minor elevations of the CPK.
Relative Cost: EMG with nerve conduction testing is $200–800 per limb.
Comments: Although EMG testing is generally considered noninvasive, patients should be told that mild to moderate discomfort may be noted. If possible, aspirin/NSAIDs should be stopped (five half-lives) before the procedure.