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What is an Electromyography test?

Electromyography (EMG) is a diagnostic procedure for assessing the function of muscles and nerves that control body movements (motor neurons). EMG helps in detecting muscle dysfunction, nerve dysfunction or nerve-to-muscle transmission issues, when symptoms of numbness, tingling or unexplained weakness in hands or legs are experienced.

Motor neurons transmit signals to muscles to initiate muscle contraction. During EMG, tiny electrodes are used to translate these electrical signals into graphs, sounds or numerical values. A specialist interprets the results for diagnosing nerve disorders, muscle disorders or neuromuscular junction (NMJ) disorders.

  1. Why is Electromyography performed?
  2. How do you prepare for an Electromyography test?
  3. How is Electromyography performed?
  4. What do Electromyography test results indicate?

Electromyography is done to check for issues with motor neurons, muscles or nerve-muscle connections. A doctor will as for this test  if the following symptoms are present:

  • Tingling or numbness
  • Weakness of muscles
  • Frequent muscles pain and cramps
  • Specific limb pain
  • Paralysis or paresis
  • Tics or involuntary muscle twitching
  • Movement issues
  • Loss of muscle mass

EMG helps in diagnosing various disease conditions, including:

This test is occasionally performed to assess the treatment response and to periodically adjust the treatment plans for various conditions.

It is crucial to inform your doctor about routine medications you are on, as well as, any over-the-counter medicines before going for an electromyography test. He/ she should also know about:

  • Your medical history, especially if you suffer from any bleeding or clotting disorder, such as haemophilia.
  • Any blood-thinning medications that you may be taking
  • Inserted medical devices, like a pacemaker, if you have any

Also, wash your skin thoroughly before the procedure (bathing) to remove excess oils. Avoid applying lotions and creams before the test.

Electromyography involves the following steps:

  • You will be asked to lie down on an examination table or sit on a reclining chair
  • Tiny electrodes will be placed at various locations on your skin depending on the area where symptoms are experienced (in some cases needle electrodes are used)
  • During the evaluation, surface electrodes transmit tiny electrical impulses (which may produce a spasm or twinge)
  • Needle electrodes may provide spontaneous electrical impulses to the muscle at res
  • In some cases, different positions are used for evaluating the affected muscles
  • Needle electrodes may produce some pain, which usually settles upon removal of electrodes
  • The procedure takes about 45 to 60 minutes

EMG usually does not carry any risk or procedure complications. However, in certain cases, needle electrodes may produce bleeding, nerve injury or infection at the site of insertion.

In case of chest muscle or intercostals muscle examination, needle electrodes may cause air leakage into the chest wall and lungs resulting in lung collapse (pneumothorax). So, it is important to talk to your doctor if you have any queries regarding the procedure.

EMG results are available immediately after the procedure is over; results appear as graphs, charts and numerical values, which are interpreted by a neurologist.

Normal investigation findings mean no muscular activity in resting muscles, which indicate healthy motor neurons and muscles.

An abnormal result of EMG indicates the presence of electrical activity in resting muscles, which may be due to:

  • Muscle disorders: Polymyositis or muscular dystrophies
  • NMJ diseases: Myasthenia gravis
  • Motor neuron diseases: Poliomyelitis or ALS

If EMG shows abnormal electrical activity to impulses during muscular contraction, it indicates

  • Nerve root compression or herniation of the disc
  • ALS (or Lou Gehrig’s Disease)
  • Carpel tunnel syndrome

Depending upon the findings of EMG, further investigations may be recommended or treatments will be provided. EMG is also used for evaluating the response to treatment; thus, periodic check using EMG is performed to adjust or alter the treatment plan (in accordance with the test outcomes) for neuromuscular conditions.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor.

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References

  1. Daroff RB, et al. Clinical electromyography. In: Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, Pa.: Saunders Elsevier; 2016
  2. KR Mills. The basics of electromyography. J Neurol Neurosurg Psychiatry 2005;76(Suppl II):ii32–ii35.
  3. Michael Rubin. Overview of Neuromuscular Junction Disorders. MSDmannual consumer version [internet]. Merck Sharp & Dohme Corp. Merck & Co., Inc., Kenilworth, NJ, USA
  4. American association of neuromuscular & electrodiagnostic medicine [internet]; FAQs-before-EDX-Testing
  5. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; Electromyography (EMG)