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Electrodiagnosis

Original Editor - Innocent Abugu

Top Contributors - Innocent Abugu, Angeliki Chorti, Jasrah Javed, Lucinda hampton and Tolulope Adeniji  

Introduction

Definition

Electrodiagnosis is an umbrella term for a range of techniques which use electrical means to understand bioelectric signals that emanate from nerves and muscles of our body. It is an integral part of diagnosis, differentiation and rehabilitation in neuromuscular disorders. [1] [2] Clinicians use electrodiagnosis when confirming a diagnosis, or establishing prognosis, severity and progression for a particular disorder. [3] [4] [5]

Historical perspective

Electricity for nerve and muscle electrophysiologic studies was applied for the first time in the 19th Century when Erb described the galvanic-faradic test. Lord Adrian then demonstrated the clinical application of strength-duration curves, and they became widely used in the assessment of peripheral nerve injuries during the 1939-45 War. [6]

Main Indications

Electrodiagnostic studies are considered an extension of clinical examination [7] and are most useful (but not exhaustive) in the workup of conditions such as: [8]

Personnel

In some countries e.g. USA, electrodiagnosis is performed by certified specialists, usually physicians (neurologists or physiatrists) specialised in the diagnosis and treatment of neuromuscular diseases and application of relevant neurophysiologic procedures. [13]

Types of Electrodiagnostic Testing

There are various electrodiagnostic testing techniques. When testing a patient, electrodiagnostic protocols are employed and these are usually a combination of the following-mentioned tests. It is imperative to perform these studies as per the protocols and guidelines that are being published from time to time. Electromyography (EMG) and Nerve Conduction Studies are the most commonly used, but there are other procedures that also fall into this category. [8] Below you can find all relevant information.

Motor Unit and Motor Unit Action Potential

A motor unit comprises of a motor neuron, its axon and all the muscle fibres innervated by that axon (Burke and Edgerton, 1975). [14] A motor unit is an anatomical and functional unit of the neuromuscular system. Electrical activity generated within a motor unit during a muscle contraction can be recorded and analysed using surface or needle electrodes. This type of electrical activity generated within a muscle and recorded by electrodes is called Motor Unit Action Potential. [15] These motor units are then analysed for shape, duration, amplitude and frequency.

Electromyography

Surface Electromyography by Paulstewart77 CC BY-SA 4.0

Electromyography (EMG) involves the evaluation and recording of muscle activity. [16] The electrical activity is recorded and converted in visual or auditory information through electromyograph. The electromyograph detects electrical potential generated by a muscle and produces a record of the muscle activity called electromyogram.

EMG is used for identifying neuromuscular diseases and disorders of motor control. EMG is usually performed with nerve conduction study. The electrical activity of a muscle can be measured using a surface electrode (surface EMG), for a large region of muscle, and a needle EMG for a smaller muscle.

Muscles are usually tested at rest and minimal muscle contraction.[8] Testing may involve various types of electrodes depending upon the protocol to be employed for that particular condition. It is imperative that the patient is told what to expect before performing the test. The test should be discontinued if the patient becomes uncomfortable or requests that it should be stopped.

The surface EMG (sEMG) is the most common, however, while it gives a good indication of which muscle groups are active, for example tremor or dystonia, it gives little information as to the fine structure of those muscles.[17] It entails placing noninvasive electrodes on the skin overlying a muscle to determine the electrical activity of that particular muscle. Surface measurements of muscle activity are generally reserved for research purposes or biofeedback. Using an adhesive electrode on the skin over the targeted area enables an easier test. However, a singular superficial electrode measurement picks up signals from multiple muscle fibres and all the tissue in between, compromising signal integrity thus making it non-viable for diagnostic uses. [18]

Needle (intramuscular) EMG entails inserting a needle electrode into a muscle, recording and amplifying the electrical signals generated from resting or contracting muscle fibers, and interpreting the signals to determine the function of the muscle fibers and motor units.[19] The needle can be relocated to a different site in the same muscle or a different muscle as needed. Due to the proximity of the needle to the muscle surface, this is a more accurate and reliable method used for clinical diagnostic purposes. This needs rigorous training and certification before one can start performing this technique. Needle EMG is the preferred method for diagnostic purposes due to being more targeted and reliable than a surface electrode. Although the process is considered safe, the potential risks of pain, bleeding, infection, and pneumothorax remain as a result of the needle being used. [20]

Single fiber electromyography (SFEMG) is a highly selective diagnostic test that involves assessment of individual muscle fiber action potentials (MFAPs). Single fiber electromyography (SFEMG) is the most sensitive electrophysiological test for myasthenia gravis and other neuromuscular junction pathology. It is also useful in the assessment of motor unit morphology in some neuromuscular diseases. [21] 

For more detailed information, you can visit Electromyogram.

Nerve Conduction Studies

Nerve conduction study also known as nerve conduction velocity test is used to measure the speed of the electrical activity of a nerve. Nerve conduction studies can test sensory or motor nerve fibers and can determine both the speed of conduction as well as the amplitude of the electrical signal evoked following stimulation of a nerve.[22] For more information about NCSs, check the Nerve Conduction Study page.

[23]

Evoked Potentials (EPs)

Evoked potentials measure electrical activity in the brain as a response to sensory stimuli.

Visual Evoked Potentials (VEPs)

Visual Evoked Potentials (VEPs) use visual stimuli (e.g. flashing patterns) to stimulate the brain, helping ophthalmologists and vision researchers assess the human visual system with methods which are otherwise unavailable. [24] Clinical applications involve visual acuity in non-verbal infants and adults with low intellectual abilities, diseases of the optic nerve, color blindness, amblyopia and field defects, surgical intra-operative monitoring. [24] [25]

Brainstem Auditory Evoked Potentials (BEAP)

Brainstem Auditory Evoked Potentials (BEAP) measure the brain's response to auditory stimulation (e.g. clicking sounds), helping with hearing assessments and identification of potential issues in the auditory nerve and brainstem pathways. [26]

Somatosensory Evoked Potentials (SEP)

Somatosensory evoked potentials (SEPs) assess the function of somatosensory pathways by stimulation of sensory nerves. SEPs may be recorded by stimulation of mixed or pure sensory nerves in the upper and lower extremities, in dermatomal areas of the skin, and from some cranial nerves with sensory function. [27]

Repetitive Nerve Stimulation (RNS)

Repetitive nerve stimulation (RNS) uses repeated transcutaneous electrical stimulation of all the motor fibers within a peripheral nerve to generate successive impulses. [28] Repetitive nerve stimulation examines the integrity of disorders of the neuromuscular junction (NMJ), such as myasthenia gravis, Lambert-Eaton syndrome, and botulism. [28]

Electrodiagnosis in Older Adults

Ageing is characterised by physiological function declines and it may be accompanied by changes such as decline in activities of daily living, impaired muscle function including postural control and muscle activation etc. These changes may impact on older adult functional ability and independent living. [29]

Electromyography(EMG) is one of the electrodiagnostic tools that can provide information about age related changes in neuromuscular adjustments and help to identify factors that may contribute to risk of falls in older adults.[30]

References

  1. ↑ Kiene J, Hiett A. Physiological Principles Underlying Electrodiagnosis and Neurophysiologic Testing. PM&R Knowledge, 2023. Available from: https://now.aapmr.org/physiological-principles-underlying-electrodiagnosis-and-neurophysiologic-testing/ [accessed 16/5/2024]
  2. ↑ Lindstrom H, Ashworth NL. The usefulness of electrodiagnostic studies in the diagnosis and management of neuromuscular disorders. Muscle Nerve. 2018 Aug;58(2):191-6.
  3. ↑ Kothari MJ, Blakeslee MA, Reichwein R, Simmons Z, Logigian EL. Electrodiagnostic studies: are they useful in clinical practice? Arch Phys Med Rehabil. 1998 Dec;79(12):1510-1.
  4. ↑ 4.0 4.1 Bolcato M, Roccaro M, Jacinto JGP, Peli A, Gentile A, Bianchi E. Use of Electrodiagnostics in the Diagnosis and Follow-Up of Brachial Plexus Syndrome in a Calf. Vet Sci. 2022 Mar 15;9(3):136.
  5. ↑ Rubin DI, Lamb CJ. The role of electrodiagnosis in focal neuropathies. Handb Clin Neurol. 2024;201:43-59.
  6. ↑ McLeod JG. Electrodiagnostic techniques. Aust J Physiother. 1968 Mar;14(1):7-10.
  7. ↑ Ginsberg MR, Morren JA, Levin K. Using and interpreting electrodiagnostic tests. Cleve Clin J Med. 2020 Nov 2;87(11):671-682
  8. ↑ 8.0 8.1 8.2 Weiss L, Weiss J, Pobre T. Oxford American Handbook of Physical Medicine & Rehabilitation. Oxford University Press, USA. 2010.
  9. ↑ Marquardt RJ, Levin KH. Electrodiagnostic Assessment of Radiculopathies. Neurol Clin. 2021 Nov;39(4):983-95.
  10. ↑ Yang DC, Lee HJ, Park JW, Nam K, Kim S, Cho KT, Kwon BS. Association Between Latency of Dermatomal Sensory-Evoked Potentials and Quantitative Radiologic Findings of Narrowing in Lumbar Spinal Stenosis. Ann Rehabil Med. 2020 Oct;44(5):353-361.
  11. ↑ Kouyoumdjian JA, Estephan EP. Electrophysiological evaluation of the neuromuscular junction: a brief review. Arq Neuropsiquiatr. 2023 Dec;81(12):1040-52.
  12. ↑ Paganoni S, Amato A. Electrodiagnostic evaluation of myopathies. Available from:https://www.statpearls.com/ArticleLibrary/viewarticle/115846 [accessed 16/5/2024]
  13. ↑ AANEM. Who is qualified to practice electrodiagnostic medicine? Available from: https://www.aanem.org/docs/default-source/documents/aanem/advocacy/who-is-qualified-to-practice-edx-medicine.pdf?sfvrsn=892d519e_2#:~:text=should%20be%20performed%20by%20a,the%20study%20of%20these%20disorders. [accessed 25/6/25]
  14. ↑ Clamann HP. Motor units and their activity during movement. InMotor Coordination 1981 (pp. 69-92). Boston, MA: Springer US.
  15. ↑ Rodríguez-Carreño I, Gila-Useros L, Malanda-Trigueros A. Motor unit action potential duration: measurement and significance. In: Advances in clinical neurophysiology 2012 Oct 17. IntechOpen.
  16. ↑ Raez MB, Hussain MS, Mohd-Yasin F. Techniques of EMG signal analysis: detection, processing, classification and applications. Biol Proced Online. 2006;8:11-35.
  17. ↑ Whittaker RG. The fundamentals of electromyography. Pract neur. 2012 Jun 1;12(3):187-94.
  18. ↑ Felici F, Del Vecchio A. Surface Electromyography: What Limits Its Use in Exercise and Sport Physiology? Front Neurol. 2020 Nov 6;11:578504.
  19. ↑ Rubin DI. Needle electromyography: basic concepts and patterns of abnormalities. Neurol Clin. 2012 May 1;30(2):429-56.
  20. ↑ Rubin DI. Needle electromyography: Basic concepts. Handb Clin Neurol. 2019;160:243-56.
  21. ↑ Lagueny A. Single-fibre electromyography. Rev Med Liege. 2004;59 Suppl 1:141-9. French.
  22. ↑ Reeves A, Swenson R. Disorders of the nervous system. Online: Dartmouth Medical School; 2008.
  23. ↑ Mohammad Sadique. Neurology#2 Nerve Conduction Velocity Studies (NVC). Available from: https://youtu.be/3FW1ZcGMW8I [accessed 25/6/2025]
  24. ↑ 24.0 24.1 Sokol S. Visually evoked potentials: theory, techniques and clinical applications. Surv Ophthalmol. 1976 Jul-Aug;21(1):18-44.
  25. ↑ Baiano C, Zeppieri M. Visual Evoked Potential. [Updated 2023 May 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK582128/
  26. ↑ Singh R, Vates E. Brainstem Auditory Evoked Response Test. [Updated 2023 Nov 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK597358/
  27. ↑ Waldman SD. Pain review. Elsevier Health Sciences; 2009 Feb 23.
  28. ↑ 28.0 28.1 Datta N, Hoke A. Repetitive Nerve Stimulation. [Updated 2023 Jul 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK594249/ [accessed 25/6/2025]
  29. ↑ Janssen TAH, Lowisz CV, Phillips S. From molecular to physical function: The aging trajectory. Curr Res Physiol. 2024 Dec 16;8:100138.
  30. ↑ Cardozo AC, Gonçalves M, Hallal CZ, Marques NR. Age-related neuromuscular adjustments assessed by EMG. Electrodiagnosis in New Frontiers of Clinical Research. Croatia: InTech. 2013 May 22:113-29.
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