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EMG Testing

EMG Testing. Edison H.Wong, M.D., M.S. Center for Pain & Medical Rehab, P.C. Ramsey Rehab Lecture Series September 29, 2009. EMG testing. What is it? Who does it? Why is it needed? What does it measure? What are results like? What is actually done? How can testing be done more easily?.

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EMG Testing

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  1. EMG Testing Edison H.Wong, M.D., M.S. Center for Pain & Medical Rehab, P.C. Ramsey Rehab Lecture Series September 29, 2009

  2. EMG testing • What is it? • Who does it? • Why is it needed? • What does it measure? • What are results like? • What is actually done? • How can testing be done more easily?

  3. What is it? • EMG is a type of Electrodiagnostic testing • Use of electrical testing to diagnose disorders of muscles and nerves • EMG stands for • Electromyelogram = graph of electrical activity in muscles • Electromyography = study of… • Electromyograph = instrument used in…

  4. Let’s be more specific • Nerves – peripheral nervous system • Sensory nerves – light touch, proprioception • Motor nerves – nerves control skeletal muscles • Muscles – skeletal muscles

  5. Who does it? • Electromyopraphers or specialists in electrodiagnostic medicine • Physiatrists or specialists in physical medicine and rehabilitation • Neurologists • May or may not be board certified: 2 boards • Technicians/Physical Therapists may perform limited portions • No Chiropractors, other practitioners

  6. Why is it needed? • Medical gold standard test for nerve function (physiological) • Better assessment of nerve damage than current imaging measures • Does not replace imaging studies (anatomical) • One of many diagnostic tools used for neuromusuclar disorders

  7. Why is testing needed? • Symptoms of nerve damage • Numbness and tingling • Funny sensations • Weakness, fatigue, clumsiness • Pain • Signs of nerve damage • Loss of or change in reflexes • Falls, gait difficulty

  8. What does it measure? • Nerve function is not a simple measure • Two parts of test • NCS/NCVS – nerve conduction study • Needle EMG • NCS uses external electricity to measure the body’s electrical pathways • Amplitudes • Conduction velocities • Sensory and motor nerves

  9. Importance of NCS • Nerves are comprised of axons and myelin sheaths • Conduction velocity affected by myelin sheath; slowing = damage • Amplitudes matter also • NCS tells only part of the story

  10. Needle EMG • Measures body’s intrinsic electrical activity generated by muscles • Spontaneous activity • Voluntary activity • Amplitudes • Frequencies • Patterns of electrical activity • Audio and visual information

  11. What are results like? • Dependent on the question asked by ordering physician • Dependent on skill of examiner • Specific diagnoses: i.e., Carpal Tunnel entrapment of Median Nerve • Non-specific diagnoses: peripheral polyneuropathy

  12. Nerve Damage • Amount of damage - relative • Mild, moderate, severe • Temporary (myelin) or permanent (axon) • Location of damage • Chronicity • Acute or ongoing • Chronic/long term

  13. Can results vary? • By skill of examiner • Limitations of testing imposed by • Patient – voluntary or involuntary • Conditions – room, equipment, etc. • Do not depend on patient symptoms! • Lack of signal does not always mean abnormality • Interpretation matters • diagnoses don’t read; “greedy” patients

  14. What is actually done? • NCS • Superficial electrodes • Stimulus probe – “zapper” • Electrical stimuli applied by individual shocks • Electricity doesn’t care where it goes • Level of stimuli safe, regulated by machine • Other limbs may be done for comparison

  15. What is actually done? • Needle EMG – Monopolar vs. Concentric • Individual muscles studied • Sampling: different nerves, proximal vs distal • Technique matters for discomfort • Relaxation matters • Paraspinal needle study important

  16. How can things be done more easily? • Expectations given to patient – like they do for MRIs • Preparation: none! • Don’t starve • Don’t be a martyr • Avoid lotions/creams – skin moisturizers! • Anxiety – premedicate • Pain – premedicate or bring with you • Temperature – cold makes a difference

  17. How can things be done more easily? • Relax – radio or listening device • Special considerations: • Lymphedema • Anticoagulation • AV fistulas • Implanted devices: AICD/pacers, stimulators • Don’t be afraid to ask questions • Get the test done but do it right!

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