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EMG Testing

EMG Testing

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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!