Electrophysiological techniques for clinical diagnosis

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Electrophysiological techniques for clinical diagnosis
PurposeAscertain electrical signals from the human body for diagnosis

Clinical Electrophysiological Testing is based on techniques derived from electrophysiology used for the clinical diagnosis of patients. There are many processes that occur in the body which produce electrical signals that can be detected. Depending on the location and the source of these signals, distinct methods and techniques have been developed to properly target them.

Contents

Role of electrophysiology in clinical medicine

Electrophysiology has a very important role in ensuring accurate clinical diagnoses. The brain, the heart and skeletal muscles are prime sources of electric and magnetic fields that can be recorded and the resulting patterns can give insight on what ailments the subject may have.

While electrophysiological tests generally passively collect electrical data, it is sometimes necessary to apply an external stimulus to the desired target in order to produce transient evoked potentials that can provide further insight not obtained from solely passive recording methods.

Electroencephalography (EEG)

Electroencephalography is the measurement of brain activity through the surface of the scalp. [1] Electroencephalography data can be viewed as a qualitative wave form, or it can be further processed through analytical procedures to produce quantitative electroencephalography (qEEG). [2] If qEEG data is mapped from multiple parts of the brain then it is a topographic qEEG (also known as brain electrical activity mapping or BEAM).

If EEGs are recorded after intentionally stimulating the brain, then the resulting data is called a event related potential. The firing of neurons throughout the brain has been known to have localized relationships to certain functions, processes and reactions to stimuli. With proper equipment it is possible to locate where in the brain neurons have been activated and measure their event related potentials. Event-related potentials can be classified as either: sensory, motor or cognitive. [3]

EEGs can be used to diagnose and monitor brain diseases such as:

Brainstem lesions in traumatic brain injury

In the event of a traumatic brain injury the presence of a brainstem lesion has a significant impact in the prognosis of the patient. Although the development of MRI has allowed for very effective detection of brainstem lesions, evoked potentials measurements are also an electrophysiological technique that has been used for over 30 years in this context. [4]

Dementia

Dementia is a progressive, degenerative brain disease that impairs cognitive functions. [5] Alzheimer's disease and other types of dementia diagnosis is being improved through the use of electroencephalogram (EEG) and event-related potentials(ERP).

Epilepsy

Abnormally excessive or synchronous neuronal activity in the brain can cause seizures. These symptoms are characteristic of the neurological disorder known as epilepsy. Epilepsy is typically diagnosed with an EEG test. [6] However, the effectiveness of MEG in the diagnosis of neocortical epilepsy has also been established. [7]

Parkinson's disease

Parkinson's disease is a degenerative ailment that affects the central nervous system and is typically identified initially by its motor related symptoms. Accurate differentiation of PD from any other neurological disorder and the identification of the disease course is important in establishing an appropriate antiparkinsonian therapy. In the diagnostic role, surface EMG is a very informative method used to obtain relevant quantitative characteristics.[ citation needed ]

Magnetoencephalography (MEG)

The measurement of the naturally occurring magnetic fields produced by the brain's electrical activity is called magnetoencephalography. This method differs from magnetic resonance imaging in that it passively measures the magnetic fields without altering the body's magnetization. However, data from MEG and MRI can be combined to create images that approximately map the estimated location of the natural magnetic fields. This composite imaging process is called magnetic source imaging (MSI).

Electrocardiography (EKG)

The heart is the muscle that pumps oxygenated blood to the whole body. In order for the heart to contract in a regular, organized manner, specific electrical signals are sent to the myocardium from the pacemaker cells. These cardiac, electrical signals produce a peculiar pattern that can be measured and analyzed. Electrocardiography is the measurement of these signals. EKGs are cheap, non-invasive and provide immediate results which has allowed for their proliferation of use in medicine. EKGs can be ordered as a one-time test, or can be continuously monitored in the case of patients wearing a holter monitor and/or admitted to a telemetry unit. EKGs provide information about heart rate, heart rhythms and provide some data on underlying myocardium, valves and coronary vessels. EKGs can be used to aid in the diagnosis of myocardial infarction, arrhythmia, left ventricular hyptertrophy, valvulopathies, and coronary artery disease.

Electromyography (EMG)

Electromyography is the measurement and analysis of the electrical activity in skeletal muscles. This technique is useful for diagnosing the health of the muscle tissue and the nerves that control them. [8] EMG measures action potentials, called Motor Unit Action Potentials (MUAPs), created during muscle contraction. A few common uses are determining whether a muscle is active or inactive during movement (onset of activity), assessing the velocity of nerve conduction, and the amount of force generated during movement. EMGs are the basis for nerve conduction studies which measure the electrical conduction velocity and other characteristics of nerves in the body. EMGs can be used to diagnose and monitor neurological diseases such as:

Carpal tunnel syndrome (CTS)

The compression of the median nerve within the carpal canal of the wrist and the progression of symptoms resulting from this entrapment is known as carpal tunnel syndrome (CTS). Nerve conduction studies have been used as a control electrophysiological method in the development of better CTS diagnostic techniques. [9]

Essential tremor

It is hard to diagnose essential tremor and differentiate it from other types of tremor. [10] The burst discharge patterns of EMG signals is compared to the frequency and amplitude of videotaped tremors to evaluate and diagnose essential tremor.

Spasticity

Spasticity is a velocity dependent resistance to stretch. [11] The most commonly affected muscles are those that oppose gravity, the elbow and wrist flexors, knee extensors and ankle plantarflexors. [12] Spasticity is a side effect of multiple central nervous system disorders including Cerebral Palsy, Stroke, Multiple Sclerosis and spinal cord injuries and results in limited joint range of motion of the affected limb. [13] Electromyography (EMG) has been proposed by multiple researchers as an alternative measurement technique to quantify spasticity. The use of EMG offers a quantitative value of severity as opposed to relying on subjective scoring protocols. [14] [15]

Multiple sclerosis

The demyelination and scarring of axons in the neurons of the nervous system can affect their conduction properties and seriously harm the normal communication of the brain with the rest of the body. Multiple sclerosis (MS) is a disease that causes this deterioration of the myelin sheath. There isn't a unique test to diagnose MS and several studies must be combined to determine the presence of this disease. However, visual evoked potentials do play a role in the whole diagnostic process. [16]

Related Research Articles

In neuroscience, an F wave is one of several motor responses which may follow the direct motor response (M) evoked by electrical stimulation of peripheral motor or mixed nerves. F-waves are the second of two late voltage changes observed after stimulation is applied to the skin surface above the distal region of a nerve, in addition to the H-reflex which is a muscle reaction in response to electrical stimulation of innervating sensory fibers. Traversal of F-waves along the entire length of peripheral nerves between the spinal cord and muscle, allows for assessment of motor nerve conduction between distal stimulation sites in the arm and leg, and related motoneurons (MN's) in the cervical and lumbosacral cord. F-waves are able to assess both afferent and efferent loops of the alpha motor neuron in its entirety. As such, various properties of F-wave motor nerve conduction are analyzed in nerve conduction studies (NCS), and often used to assess polyneuropathies, resulting from states of neuronal demyelination and loss of peripheral axonal integrity.

<span class="mw-page-title-main">Lambert–Eaton myasthenic syndrome</span> Medical condition

Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness of the limbs.

Neuromyotonia (NMT) is a form of peripheral nerve hyperexcitability that causes spontaneous muscular activity resulting from repetitive motor unit action potentials of peripheral origin. NMT along with Morvan's syndrome are the most severe types in the Peripheral Nerve Hyperexciteability spectrum. Example of two more common and less severe syndromes in the spectrum are Cramp Fasciculation Syndrome and Benign Fasciculation Syndrome. NMT can have both hereditary and acquired forms. The prevalence of NMT is unknown.

<span class="mw-page-title-main">Neurology</span> Medical specialty dealing with disorders of the nervous system

Neurology is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the spinal cord and the peripheral nerves. Neurological practice relies heavily on the field of neuroscience, the scientific study of the nervous system.

Clinical neurophysiology is a medical specialty that studies the central and peripheral nervous systems through the recording of bioelectrical activity, whether spontaneous or stimulated. It encompasses both research regarding the pathophysiology along with clinical methods used to diagnose diseases involving both central and peripheral nervous systems. Examinations in the clinical neurophysiology field are not limited to tests conducted in a laboratory. It is thought of as an extension of a neurologic consultation. Tests that are conducted are concerned with measuring the electrical functions of the brain, spinal cord, and nerves in the limbs and muscles. It can give the precise definition of site, the type and degree of the lesion, along with revealing the abnormalities that are in question. Due to these abilities, clinical neurophysiology is used to mainly help diagnose diseases rather than treat them.

An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light flash or a pure tone. Different types of potentials result from stimuli of different modalities and types. Evoked potential is distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiologic recording method. Such potentials are useful for electrodiagnosis and monitoring that include detections of disease and drug-related sensory dysfunction and intraoperative monitoring of sensory pathway integrity.

<span class="mw-page-title-main">Demyelinating disease</span> Any neurological disease in which the myelin sheath of neurons is damaged

A demyelinating disease refers to any disease affecting the nervous system where the myelin sheath surrounding neurons is damaged. This damage disrupts the transmission of signals through the affected nerves, resulting in a decrease in their conduction ability. Consequently, this reduction in conduction can lead to deficiencies in sensation, movement, cognition, or other functions depending on the nerves affected.

<span class="mw-page-title-main">Electromyography</span> Electrodiagnostic medicine technique

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyograph detects the electric potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect abnormalities, activation level, or recruitment order, or to analyze the biomechanics of human or animal movement. Needle EMG is an electrodiagnostic medicine technique commonly used by neurologists. Surface EMG is a non-medical procedure used to assess muscle activation by several professionals, including physiotherapists, kinesiologists and biomedical engineers. In computer science, EMG is also used as middleware in gesture recognition towards allowing the input of physical action to a computer as a form of human-computer interaction.

<span class="mw-page-title-main">Nerve conduction study</span> Diagnostic test for nerve function

A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical specialists such as clinical neurophysiologists, physical therapists, chiropractors, physiatrists, and neurologists who subspecialize in electrodiagnostic medicine. In the United States, neurologists and physiatrists receive training in electrodiagnostic medicine as part of residency training and in some cases acquire additional expertise during a fellowship in clinical neurophysiology, electrodiagnostic medicine, or neuromuscular medicine. Outside the US, clinical neurophysiologists learn needle EMG and NCS testing.

Intraoperative neurophysiological monitoring (IONM) or intraoperative neuromonitoring is the use of electrophysiological methods such as electroencephalography (EEG), electromyography (EMG), and evoked potentials to monitor the functional integrity of certain neural structures during surgery. The purpose of IONM is to reduce the risk to the patient of iatrogenic damage to the nervous system, and/or to provide functional guidance to the surgeon and anesthesiologist.

Monoplegia is paralysis of a single limb, usually an arm. Common symptoms associated with monoplegic patients are weakness, numbness, and pain in the affected limb. Monoplegia is a type of paralysis that falls under hemiplegia. While hemiplegia is paralysis of half of the body, monoplegia is localized to a single limb or to a specific region of the body. Monoplegia of the upper limb is sometimes referred to as brachial monoplegia, and that of the lower limb is called crural monoplegia. Monoplegia in the lower extremities is not as common of an occurrence as in the upper extremities. Monoparesis is a similar, but less severe, condition because one limb is very weak, not paralyzed. For more information, see paresis.

EEG-fMRI is a multimodal neuroimaging technique whereby EEG and fMRI data are recorded synchronously for the study of electrical brain activity in correlation with haemodynamic changes in brain during the electrical activity, be it normal function or associated with disorders.

<span class="mw-page-title-main">Electroencephalography</span> Electrophysiological monitoring method to record electrical activity of the brain

Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex. It is typically non-invasive, with the EEG electrodes placed along the scalp using the International 10–20 system, or variations of it. Electrocorticography, involving surgical placement of electrodes, is sometimes called "intracranial EEG". Clinical interpretation of EEG recordings is most often performed by visual inspection of the tracing or quantitative EEG analysis.

Cramp fasciculation syndrome (CFS) is a rare peripheral nerve hyperexcitability disorder. It is more severe than the related disorder known as benign fasciculation syndrome; it causes fasciculations, cramps, pain, fatigue, and muscle stiffness similar to those seen in neuromyotonia. Patients with CFS, like those with neuromyotonia, may also experience paresthesias. Most cases of cramp fasciculation syndrome are idiopathic.

Electromyoneurography (EMNG) is the combined use of electromyography and electroneurography This technique allows for the measurement of a peripheral nerve's conduction velocity upon stimulation (electroneurography) alongside electrical recording of muscular activity (electromyography). Their combined use proves to be clinically relevant by allowing for both the source and location of a particular neuromuscular disease to be known, and for more accurate diagnoses.

Electrodiagnosis (EDX) is a method of medical diagnosis that obtains information about diseases by passively recording the electrical activity of body parts or by measuring their response to external electrical stimuli. The most widely used methods of recording spontaneous electrical activity are various forms of electrodiagnostic testing (electrography) such as electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). Electrodiagnostic medicine is a medical subspecialty of neurology, clinical neurophysiology, cardiology, and physical medicine and rehabilitation. Electrodiagnostic physicians apply electrophysiologic techniques, including needle electromyography and nerve conduction studies to diagnose, evaluate, and treat people with impairments of the neurologic, neuromuscular, and/or muscular systems. The provision of a quality electrodiagnostic medical evaluation requires extensive scientific knowledge that includes anatomy and physiology of the peripheral nerves and muscles, the physics and biology of the electrical signals generated by muscle and nerve, the instrumentation used to process these signals, and techniques for clinical evaluation of diseases of the peripheral nerves and sensory pathways.

Electrography often refers to electrophotography, that is, Kirlian photography.

<span class="mw-page-title-main">Monomelic amyotrophy</span> Medical condition

Monomelic amyotrophy (MMA) is a rare motor neuron disease first described in 1959 in Japan. Its symptoms usually appear about two years after adolescent growth spurt and is significantly more common in males, with an average age of onset between 15 and 25 years. MMA is reported most frequently in Asia but has a global distribution. It is typically marked by insidious onset of muscle atrophy of an upper limb, which plateaus after two to five years from which it neither improves nor worsens. There is no pain or sensory loss associated with MMA. MMA is not believed to be hereditary.

An electrogram (EGM) is a recording of electrical activity of organs such as the brain and heart, measured by monitoring changes in electric potential.

Bioelectromagnetic medicine deals with the phenomenon of resonance signaling and discusses how specific frequencies modulate cellular function to restore or maintain health. Such electromagnetic (EM) signals are then called "medical information" that is used in health informatics.

References

  1. ↑ L. Jasmin "EEG"
  2. ↑ Duffy, FH; Hughes, JR; Miranda, F; Bernad, P; Cook, P (October 1994). "Status of quantitative EEG (QEEG) in clinical practice, 1994" (PDF). Clinical Electroencephalography. 25 (4): VI–XXII. doi:10.1177/155005949402500403. PMID   7813090. S2CID   29808694. Archived from the original (PDF) on 2015-02-17.
  3. ↑ Bressler, S. L. and Ding, M. 2006. "Event-Related Potentials". Wiley Encyclopedia of Biomedical Engineering.
  4. ↑ Wedekind, Christoph; Hesselmann, Volker; Klug, Norfrid (August 2002). "Comparison of MRI and electrophysiological studies for detecting brainstem lesions in traumatic brain injury". Muscle & Nerve. 26 (2): 270–273. doi:10.1002/mus.10187. PMID   12210392. S2CID   22187426.
  5. ↑ Ifeachor, E. C., et al, "Biopattern Analysis and Subject-Specific Diagnosis and Care of Dementia "., Engineering in Medicine and Biology 27th Annual Conference, September 2005
  6. ↑ A.D.A.M. Medical Encyclopedia., "Epilepsy - PubMed Health". Retrieved 27 July 2012
  7. ↑ H. Stefan, "The Role of MEG in Epilepsy Diagnosis and Treatment", ACNR, Volume 4, No 2, May/June 2004
  8. ↑ Mayo Clinic Staff, "Electromyography (EMG)". Retrieved 27 July 2012
  9. ↑ Yagci, Ilker; Gunduz, Osman Hakan; Sancak, Seda; Agirman, Mehmet; Mesci, Erkan; Akyuz, Gulseren (May 2010). "Comparative electrophysiological techniques in the diagnosis of carpal tunnel syndrome in patients with diabetic polyneuropathy". Diabetes Research and Clinical Practice. 88 (2): 157–163. doi:10.1016/j.diabres.2010.02.011. PMID   20223548.
  10. ↑ Louis, Elan D.; Pullman, Seth L. (July 2001). "Comparison of Clinical vs Electrophysiological Methods of Diagnosing of Essential Tremor" (PDF). Movement Disorders. 16 (4): 668–673. doi:10.1002/mds.1144. PMID   11481690. S2CID   39351295. Archived from the original (PDF) on 2015-10-09. Retrieved 2012-07-28.
  11. ↑ Lance, J.W., The control of muscle tone, reflexes, and movement: Robert Wartenberg Lecture, Neurology, 30 (1980) 1303- 1313.
  12. ↑ Ansari, NN; Naghdi, S; Arab, TK; Jalaie, S (2008). "The interrater and intrarater reliability of the Modified Ashworth Scale in the assessment of muscle spasticity: limb and muscle group effect". NeuroRehabilitation. 23 (3): 231–7. doi:10.3233/NRE-2008-23304. PMID   18560139.
  13. ↑ "Exede Satellite Internet | Exede Internet". Archived from the original on 2012-09-20. Retrieved 2012-11-01.
  14. ↑ Malhotra, S; Cousins, E; Ward, A; Day, C; Jones, P; Roffe, C; Pandyan, A (2008). "An investigation into the agreement between clinical, biomechanical, and neurophysiological measures of spasticity". Clinical Rehabilitation. 22 (12): 1105–1115. doi:10.1177/0269215508095089. PMID   19052249. S2CID   42750524.
  15. ↑ Castilho, J.; Ferreira, L. A. B.; Pereira, W. M.; Neto, H. P.; Morelli, J. G. S.; Brandalize, D.; Kerppers, I. I.; Oliveria, C. S. (July 2012). "Analysis of electromyographic activity in spastic biceps brachii muscle following neural mobilization". Journal of Bodywork and Movement Therapies. 16 (3): 364–368. doi:10.1016/j.jbmt.2011.12.003. PMID   22703748.
  16. ↑ McDonald, W. I.; Compston, A.; Edan, G.; Goodkin, D.; Hartung, H.-P.; Lublin, F. D.; McFarland, H. F.; Paty, D. W.; Polman, C. H.; Reingold, S. C.; Sandberg-Wollheim, M.; Sibley, W.; Thompson, A.; Van Den Noort, S.; Weinshenker, B. Y.; Wolinsky, J. S. (July 2001). "Recommended diagnostic criteria for multiple sclerosis: Guidelines from the international panel on the diagnosis of multiple sclerosis" (PDF). Annals of Neurology. 50 (1): 121–127. CiteSeerX   10.1.1.466.5368 . doi:10.1002/ana.1032. PMID   11456302. S2CID   13870943.
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