# Electromyography | Symptoms, Causes, Tests and Treatment | OSANG > Electromyography (EMG), which is performed together with nerve conduction study (NCS), is a key diagnostic tool to differentiate lesions of peripheral nerves, nerve root… - Official page: https://osns.co.kr/en/encyclopedia/electromyography - Organization: OSANG Neurosurgery ## Page content Diagnostic Tools ## Electromyography Electromyography Electromyography (EMG) is an electrophysiological test that evaluates the type, location, and severity of neuromuscular disease by inserting a needle electrode into the muscle and recording and analyzing electrical activity at rest and during contraction. ## At a glance Electromyography (EMG), which is performed together with nerve conduction study (NCS), is a key diagnostic tool to differentiate lesions of peripheral nerves, nerve roots, neuromuscular junction, and muscles themselves. Abnormal spontaneous potentials (fibrillation potentials, positive sharp waves) at rest indicate denervation, and analysis of motor unit potential (MUP) during contraction distinguishes between neurogenic and muscular lesions. In diagnosing radiculopathy, it has a sensitivity of about 50-70% and a specificity of about 85-90%. - 01Definition and Overview - 02inspection process - 03Interpretation of results - 04clinical application - 05Limitations of the test - 06Precautions before inspection ## Definition and Overview Electromyography (EMG) is a test that records and analyzes muscle electrical activity at rest and at various contraction strengths by inserting a disposable concentric needle electrode into the muscle. It is performed together with nerve conduction testing (NCS) and constitutes an 'electrodiagnostic study', and plays a key role in the differential diagnosis of peripheral nervous system and muscle diseases. ## inspection process ### Insertional and spontaneous activity Electrical activity is observed during needle insertion and when the muscle is fully relaxed. - insertional activity: Electrical activity that occurs when a needle is inserted or moved. Increase or decrease has pathological significance. - Normal: no electrical activity at rest (electrical silence) - Abnormal spontaneous potentials: a finding indicative of denervation The types of abnormal spontaneous potentials are as follows. - Fibrillation potential: Voluntary contraction of individual denervated muscle fibers. Regular and biphasic waveforms - Positive sharp wave: Same meaning as fibrillation potential. Characteristic initial positive deflection - myotonic discharge: “diving bomb” sound. Characteristic in muscular rigidity - Fasciculation potential: Voluntary contraction of an entire motor unit. Significance in motor neuron disease ### Voluntary motor unit analysis The motor unit potential (MUP) is analyzed as the patient gradually contracts the muscles. The measurement indicators are as follows. - MUP amplitude: reflects the number of muscle fibers within the motor unit - MUP duration: reflects the area of the motor unit - MUP polyphasic rate: increases during reinnervation or myopathy. - Recruitment pattern: number of motor units activated and firing frequency ## Interpretation of results ### Neurogenic pattern When motor nerves are damaged, spontaneous potentials appear in denervated muscle fibers, and surviving motor nerves expand motor units through reinnervation. - At rest: Fibrillation potential, positive sharp wave (+) - MUP changes: increased amplitude, increased duration, increased polyphasic (giant MUP) - Recruitment pattern: reduced recruitment — fewer motor units are activated, and the firing frequency of individual motor units increases. - Representative diseases: radiculopathy, peripheral nerve damage, motor neuron disease (ALS) ### Myopathic pattern When the muscle fiber itself is damaged, the size of the motor unit is reduced. - At rest: Normal in most cases (spontaneous displacement possible in some inflammatory myopathies) - MUP changes: decreased amplitude, decreased duration, increased polyphasic (small polyphasic MUP) - Recruitment pattern: early recruitment—large numbers of small motor units are recruited during weak contractions - Representative diseases: polymyositis, dermatomyositis, muscular dystrophy, metabolic myopathy ### Neuromuscular junction lesions It is evaluated using repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG). In myasthenia gravis, a decrease in CMAP amplitude is characteristic during low-frequency (2-3 Hz) repetitive stimulation. ## clinical application ### Radiculopathy Electromyography plays a complementary role to imaging (MRI) in diagnosing radiculopathy. - Denervation is confirmed in the distribution of muscles controlled by the corresponding nerve root. - The finding of denervation of the paraspinal muscles suggests that the lesion is proximal to the intervertebral foramen (nerve root level). - It is useful in distinguishing clinically significant nerve root compression from anatomical abnormalities seen on MRI. - The timing of the test is important because denervation is fully evident 3 to 4 weeks after symptom onset. ### Motor neuron disease (ALS) Extensive denervation and reinnervation are found in various parts of the body (brainstem, cervical spine, thoracic spine, and lumbosacral spine), and sensory nerve conduction tests are normal. Fasciculation is commonly observed. In the Awaji diagnostic criteria, EMG findings are recognized as objective evidence of clinical involvement. ### myopathy In inflammatory myopathies such as polymyositis and dermatomyositis, spontaneous potentials and myopathy patterns are observed during the active phase, and EMG is also used to select muscle biopsy sites. ### traumatic nerve injury Tracking the extent of denervation and progress of reinnervation after nerve injury helps determine the timing of surgical intervention. ## Limitations of the test - Invasive testing (needle insertion) causes discomfort to the patient. - The experience and skill of the examiner (neurologist) affects the interpretation of the results. - In the acute phase (within 1 to 2 weeks after symptom onset), denervation may not yet appear. - Examination may be limited for deep muscles or muscles that are difficult to access. - Because the patient's cooperation (voluntary muscle contraction) is required, it is limited in patients with impaired consciousness or severe pain. ## Precautions before inspection - No special fasting needed - Can be performed in most cases even while taking anticoagulants (caution when testing deep muscle) - Do not apply moisturizer or lotion to the test area. - People with pacemakers must be notified before testing. ## Frequently asked questions ### Q01Does electromyography hurt a lot? There is some discomfort because a thin needle is inserted into the muscle, but this is a level that most patients can tolerate. Electrodes that are much thinner than injection needles (approximately 0.3 to 0.5 mm in diameter) are used, and the risk of bleeding or infection after the test is very low. The test time is approximately 30 to 60 minutes. ### Q02Are electromyography and nerve conduction testing the same? Although they are different tests, they are mostly performed together. Nerve conduction studies (NCS) evaluate the electrical conduction of the nerves themselves, and electromyography (EMG) evaluates the electrical activity of muscles. The combination of the two tests is called an ‘electrodiagnostic study’ and accurately determines the location and type of the lesion. ### Q03What is denervation in electromyography? Denervation is a condition in which the nerve supply to the muscle is cut off due to damage to the motor nerve that controls the muscle. It is identified as an abnormal spontaneous potential (fibrillation potential, positive sharp wave) at rest, and appears in radiculopathy, peripheral nerve damage, and motor neuron disease. ### Q04Can the test be done if I am taking blood thinners (anticoagulants)? Most tests are possible. It can be performed even while taking aspirin or clopidogrel. There is a slightly higher risk of minor bleeding at the needle insertion site during use of warfarin or NOACs, but most muscles can be tested safely. Caution is required when examining deep muscles. ### Q05How long does it take for test results to come back? Because electromyography results are read in real time, you can receive an explanation of the results immediately after the test or within the same day. The neurologist performing the test directly inserts the needle, analyzes the waveform, and interprets it in conjunction with the clinical findings. ## Related articles - Amyloid PET - Cognitive function test - pupillometry test - Valsalva test This article provides general medical information and does not replace an individual diagnosis or treatment plan. Please seek a medical assessment if symptoms persist. ## Important notice This Markdown alternative helps search and AI tools understand the public page accurately. It provides general health information and does not replace an individual diagnosis or treatment.