Electrodiagnosis

Electrodiagnosis is a field which makes use of Electrophysiology in the study of human neurophysiology with the aid of electricity. Neurodiagnostics(NDS), electromyography(EMG) and evoked potentials(EPs) are some of the fundamental principles that are used in electrodiagnosis.

Electrodiagnostic testing is a critical tool in evaluating peripheral nerve or muscle injury, muscle diseases, or the localization of the problem prior to developing a treatment strategy. While electrodiagnostic tests are functional, they fundamentally differ from structures like the MRI that provides an image of the body’s anatomy. For instance, a patient may experience severe pain at the back while the MRI scan may be normal; on the other hand, individuals may have disk protrusions but have no complaints. Thus, electrodiagnostic studies can be helpful in cases where other diagnostic modalities seem insufficient. There are physiatrists with specialization and training in physical medicine and rehabilitation, neurologists, anesthesiologists among others who are qualified to perform electrodiagnostic tests.

Electromyography

The first electrodiagnostic test is Electromyography (EMG) where the needle is inserted to record the muscle activity at rest, with mild contraction, and contraction with maximum force. Usually, muscles do not have electrical activity at rest, however, myopathic fibers may exhibit spontaneous contraction during examination.

Damage to the nerve leading to neurotmetic or axonotmetic lesions causes Wallerian degeneration and produces spontaneous fibrillations and positive sharp wave activity in the period of rest. EMG can also establish primary muscle disorders.

Contractile relations in muscle fibres are determined during voluntary movement. Normal recruitment starts at 15-20 Hz as individual muscle fibers become recruited one after the other. Although identifying these patterns may sometimes be difficult and requires the use of advanced computerized equipment, they are critical during the assessment of the severity of the injuries and the prognosis since the strength of the signals does not depend on the cooperation of the patient.

In a study by Impastato et al., it was reported that voluntary motor unit recruitment at 1-9 months after trauma may be a predictor of unfavourable outcome for patients with traumatic brachial plexus injury. Overall, by 1.4 years post-injury, only 25% of muscles with severely reduced recruitment had a strength greater than 3/5.

While taking EMG can be somewhat painful due to the use of needles, there is enhanced technology in the market that involve smaller recording needles. The electromyographers should be up to date and have the right accreditation to avoid discomfort to patients. One emerging concern that has been evidenced is the expansion of EMG performance by nonphysician personnel, since the procedure involves highly technical skills and disease-specific knowledge to produce a reliable interpretation.

Nerve conduction studies

Nerve conduction studies (NCS) are mandatory for electrodiagnostic examinations which deliver electrical stimuli through peripheral nerves and evaluate muscle responses. Electrodiagnostic tests including latency, distance and nerve conduction velocity (NCV) provided information on the nerve and myelination. NCS can determine injury location, for example in carpal tunnel syndrome and can also determine other various nerve injuries and entrapments.

Studies prove that NCS outcomes may differ in diabetic peripheral neuropathy; major challenges in assessing clinical phenotypes exist. Conduction velocity correlates with nerve diameter, which suggests that only myelinated fibre’s diameter increases and reduces the capacity to measure small fibres neuropathy. Moreover, NCS can give furthermore false-positive results than ultrasonography in diagnosis of the asymptomatic carpal tunnel syndrome. However, in acute injuries, NCS continues to be useful since it can detect changes in motor unit recruitment proximal to the nerve stump in complete nerve transection.

Evoked Potentials

EPs refers to the electrical responses of the nervous system to sensory stimulation, more specifically diagnosing the CNS through electrodiagnostic approaches.

Types of EPs include:

• Somatosensory EPs (SSEPs)
• Visual EPs (VEPs)
• Brainstem auditory EPs (BSAEPs)
• Dermatomal EPs
• Myotomal EPs

SSEPs, the most common, entail activating an extremity and acquiring a response from the scalp that helps in determining the site and extent of nerve root or CNS damage. They are most useful for cases such as multiple sclerosis and chronic inflammatory demyelinating polyneuropathy (CIDP). SSEPs are also useful in the evaluation of coma and brain death and general anesthesia guidelines recommend using total intravenous rather than gas anaesthesia during the procedure. VEPs elicit activity of the optic nerve and traces the responses in the visual cortex to identify damages along the optic tract.

BSAEPs work with auditory clicks to evaluate the cochlear nerve and identify the position of auditory pathway damage. In surgical scenarios, EPs are used to evaluate the condition of the spinal cord, in which intraoperative SSEPs reduce the likelihood of a permanent injury by about 50% since they offer updates to the surgeons.

Pacemakers or Implantable Cardioverter Defibrillators: During electrodiagnostic testing including nerve conduction studies, electrical stimulation could affect the proper working of these devices. Measures should be applied, or the test may not be conducted where it is necessary.

Severe bleeding disorders: Having hemophilia or taking anticoagulants exposes one to developing excess bleeding or hematoma when performing needle EMG. In such circumstances, diversification of methods needed for diagnosis could be required.

Active infections at the test site: Needle EMG may be contraindicated if there is a localized infection or an open wound in the area that the test is to be conducted to prevent spread of infection.

Uncooperative or noncompliant patients: This is because some of the patients may develop discomfort or may not be willing to undergo the tests and thus give inconclusive results. This can be even true in some events with use of children below certain ages or patient with certain mental diseases.

Allergies to materials used in the procedure: An important thing to note is that in case where a patient develops an allergic reaction to electrodes, gels employed in the tests, though this is hardly frequent, the patient will require to change the type of electrode to be used, or the manner of test administration will have to be altered.