Eeg Montages

In the recording of the EEG, electrodes are typically placed on the scalp using the 10-20 system (Fig. 5). In this standardized method, contacts are named by their location (frontopolar, frontal, central, parietal, temporal, occipital, and auricular). They are also numbered with odd numbers over the left hemisphere, even numbers over the right, and z referring to the midline. The particular sequence in which the EEG data is displayed is called the montage. Montages may be bipolar or...

Two Other Concepts Relevant To Volume Conduction Theory

All recordings in clinical neurophysiology are differential recordings, in that the electrical activity under one electrode (the active electrode or E1) is compared with that under the other electrode (the reference or inactive electrode, called E2). The final waveform obtained is a combination of what the E1 and the E2 electrodes are sensing in mathematical terms, this would be described as E1 - E2. Hence, whatever E2 is seeing needs to be subtracted from E1. Two terms are used to describe the...

What Is Volume Conduction Why Is It Relevant

Volume conduction is the term used to describe the effects of recording electrical potentials at a distance from their source generator. In other words, the recording electrodes are not in direct contact with the nerve or muscle there is a medium of some sort separating the two. In truth, volume conduction plays a role in almost all clinical neurophysiological recordings, both central and peripheral, because recording electrodes are never placed in direct contact with the nerve cells generating...

James B Caress

Nerve conduction studies and their interpretation are subject to a variety of factors. First, technical factors including submaximal stimulation, environmental electrical noise, inaccurate placement of the recording electrodes, and stimulus artifact can substantially interfere with accurate recording of nerve and muscle responses. Second, physiological factors, such as the effects of body height and age, can cause profound variation in all nerve conduction parameters, and studies require...

Christopher M Sinclair Mason C Gasper and Andrew S Blum

A basic understanding of simple electronics is vital for the student of clinical neurophysiology to better understand how we begin to analyze neurobiological systems. The elements of basic circuits have relevant and tangible application to the way in which we model the behavior of neural systems in the laboratory. This chapter helps to define and assemble these varied circuit elements for the student. This base of understanding is then used to illustrate how simple electronic circuits can...

Introduction

EEG is an important tool in pediatric neurology. EEG abnormalities occur in all categories of neurological disorders. These abnormalities are useful for lateralizing and localizing a neurological process, but are nonspecific and do not make a specific diagnosis. Epileptiform activity, described as an EEG waveform recorded in a proportion of those suffering from an epileptic disorder, may occur in conditions other than epilepsy. Therefore, the presence of overt epileptiform features suggests,...

Bernard S Chang and Frank W Drislane

Despite the advances in neuroimaging technology in recent decades, the EEG is still the cornerstone of diagnostic testing for patients with epilepsy, and it remains the best real-time assessment of cerebral physiological function available. For patients with suspected seizure disorders, the routine EEG is used by clinicians to identify the presence of interictal epileptiform discharges that serve as a marker for epilepsy, and more prolonged ambulatory or inpatient EEG monitoring is used to...

Physiological Considerations

The majority of radiculopathies result from nerve root compression, either from disc her-niation or as a consequence of spondylotic arthropathy inflammatory and immunological lesions are less common. The most commonly involved roots are L5 and S1, and C6 and C7 (see Table 1 for a list of radiculopathies and associated symptoms and signs). These lesions may affect nerve roots by causing axonal degeneration, focal demyelination, or both. The electrophysiological findings in a patient are...

Nerve Conduction Studies

In the evaluation of PNs, routine motor and sensory nerve conduction studies are performed, usually starting with the lower extremities. If asymmetry is suggested by history or examination, the more-affected limb is evaluated first, followed by the contralateral lower extremity. Nerve conduction studies of the upper extremities can provide additional information regarding the pathophysiology of PN (e.g., demyelinating features), especially if the lower extremity motor and sensory responses are...

Electrical Safety

Electrodiagnostic procedures are extremely safe, however, injuries can occur and may include pain, dermal burns, seizure, and ventricular fibrillation. A current of 1 mA at 60 Hz applied to dry skin is the threshold for pain sensation. Lethal current injury causing ventricular fibrillation exceeds 100 to 300 mA. Be aware of low-resistance pathways between external current sources and the heart (e.g., indwelling cardiac catheters), because currents less than 100 mA can cause serious cardiac...

Drug Or Drug Withdrawal

Drugs, or the withdrawal of drugs, can precipitate seizures. Historically, pentylenetetrazol (Metrazol) was introduced to bring on convulsive seizures for electroconvulsive shock therapy in the 1930s and 1940s. It was later abandoned because of many restrictions on its use. Antiepileptic drug withdrawal is often used during inpatient long-term video EEG monitoring for both diagnostic and therapeutic reasons. Contrary to many patients' understanding, however, drug withdrawal is rarely used in...

Cell Membrane Icf And

The cell membrane separates the ICF from the ECF, and helps to maintain critical differences in ionic concentrations between the two fluid spaces. Of the electrically important ion species, sodium concentration is approximately 12 times greater in the ECF than in From The Clinical Neurophysiology Primer Edited by A. S. Blum and S. B. Rutkove Humana Press Inc., Totowa, NJ the ICF, whereas chloride concentration is approx 25 times greater in the ECF than the ICF. Potassium, however, is approx 35...

Recording Principals

EEG recording electrodes are glued onto the scalp in an orderly fashion according to an agreed on measured placement, referred to as either the International 10-20 or 10-10 system (1). The electrodes are plugged into a head-box, which allows the technician to record in either a bipolar or a referential fashion. The former is a system in which adjacent electrodes are connected to a differential amplifier. The latter is a system in which each electrode is connected to a differential amplifier and...

Devanand Jillapalli and Jeremy M Shefner

The neuron is uniquely suited for the transmission of electrical impulses. The neuronal membrane itself allows for charge separation depending on the permeability of the membrane to a given type of ion, that ion will distribute across the membrane, producing a resting membrane potential, described by the Nernst equation. However, via the sodium-potassium (Na-K) pump, an active electrochemical gradient is maintained across the cell membrane, the magnitude of which can be calculated by knowing...

Skin Preparation

Good skin preparation is vital to performing NCS. The skin acts as a barrier to the measurement of electrical signals of interest and the effect of this barrier can be minimized by application of conductive gel that provides a low-resistance pathway to the electrode. Thick or edematous skin adds additional distance between the recording electrodes and the signal generator (i.e., the nerve or muscle), resulting in lower amplitudes. When the skin is callused, there may be different amounts of...

The Awake And Resting State

After the electrodes are attached, the montage selected and the machine calibrated, the technician is ready to record. Recordings are done for between 20 min (minimum) and several hours in selected circumstances. The patient is recorded initially in the awake resting state, with eyes open, and recorded again with eyes closed. Unless there is a specific reason to the contrary, part of the recording session should be performed with the patient hyperventilating and receiving intermittent photic...

Amplifiers

Amplifiers are electronic devices that serve to multiply an input signal by a constant. This amplification factor is called gain and is related to the ratio, Vou Vin. It is common to express gain in decibels as 20 x log10(Vou Vin). The dynamic range of an amplifier refers to the voltage range over which the amplifier behaves linearly. The sensitivity control on an EEG machine helps to modify the dynamic range of the amplifier. Sensitivity is expressed as microvolts per millimeter and refers to...

Celltocell Communication

Through either neurotransmitter release at chemical synapses or current flow through gap junctions, ligand-gated or voltage-gated channels open and elicit postsynaptic potentials. Postsynaptic potentials alter the probability that an action potential will be produced in the postsynaptic cell. If there is depolarization of the membrane, the potential is termed an excitatory postsynaptic potentials (EPSP), whereas, if there is hyperpolarization, the potential is called an inhibitory postsynaptic...

Power

Energy is simply charge moving across some potential energy gradient (E QV). Power is the rate of transfer of this energy, or mathematically A useful permutation of power for use in electrical circuits is as follows where I is the current and V is the voltage. The SI unit of power is the watt (W), which is equivalent to 1 J s (energy per time). Recall the previous transformer discussion. As the voltage climbs, the current drops proportionally, and the product of these (the power) will remain...

Time Constants

With this understanding of basic circuit elements, we can now examine how simple circuits behave and permit basic electronic filtering of waveform data. An RC circuit is shown in Fig. 3A. When voltage is applied to the circuit, current flows across the resistor and begins to accumulate on the capacitor. As the capacitor becomes fully charged, it accrues a voltage that opposes further flow of current through the circuit. If the power source is turned off, the capacitor discharges in the opposite...

Suggested Reading

Albers JW, Donofrio PD, McGonagle TK. Sequential electrodiagnostic abnormalities in acute inflammatory demyelinating polyradiculoneuropathy. Muscle Nerve 1985 8 528-539. Dumitru D. Physiologic basis of potentials recorded in electromyography. Muscle Nerve 2000 23 1667-1685. Fraser JL, Olney RK. The relative diagnostic sensitivity of different F-wave parameters in various polyneuropathies. Muscle Nerve 1992 15 912-918. Kincaid JC, Brasher A, Markand ON. The influence of the reference electrode...

Generalized Ictal Patterns

The Evolving Discharge of a GTC Seizure The onset of a GTC seizure on EEG is typically characterized by the rapid (> 10 per second) repetition of generalized spikes and polyspikes. These spikes usually increase in amplitude and decrease in frequency during the first 10 to 20 s of a GTC seizure, corresponding to the tonic phase observed clinically. As the clonic phase ensues, bursts of generalized high-amplitude spike-and-slow wave or polyspike discharges may be observed coinciding...

Median Neuropathy

The median nerve can be compressed at various levels the most common site being at the wrist. This neuropathy is the most common entrapment neuropathy affecting the upper extremity. The median nerve arises from the medial and lateral cords of the brachial plexus. The lateral cord is made up of C6-C7 fibers, and supplies median sensory fibers to the thenar eminence, thumb, index, and middle fingers, as well as, the majority of motor fibers to the proximal median-innervated forearm muscles. The...

Response To Hyperventilation

Hyperventilation is a method of activating the EEG. It may bring out focal or generalized slowing in cases of structural disease or of more diffuse encephalopathy disorders. It also can bring out interictal epileptic discharges or trigger more overt symptomatic seizures. It should not be performed in the very elderly patient or in someone suspected of having any intracranial mass lesions or a recent transient ischemic event stroke. In the adult population, it is normal to hyperventilate the...

Review Questions

What is responsible for voltage potentials across neuronal membranes 2. What forces govern ionic flow through neuronal channels 3. Which ion is most important for determining the resting membrane potential Why 4. What are the two main mechanisms that permit gating of channel opening 5. What is the main channel that, in a feed-forward fashion, leads to the rapid depolarization intrinsic to the action potential Which ion facilitates repolarization 6. As neuronal size increases, does...

Sciatic Neuropathy

The sciatic nerve derives its supply from the L4-S2 nerve roots. The nerve arises from the lumbosacral plexus, and exits the pelvis through the greater sciatic foramen before traveling under the piriformis muscle. The nerve itself consists of two distinct trunks, the lateral trunk (peroneal) and medial trunk (tibial). Branches originating in the proximal thigh arise predominantly from the tibial division. The tibial division supplies the hamstring muscles, with the exception of the short head...

Neurophysiology Of Neuromuscular Transmission 11 Anatomy of the Terminal End Plate Region

The physiology of the neuromuscular junction (NMJ) derives from the anatomy of the terminal axon and motor end plate, also referred to as the presynaptic and postsynaptic regions (Fig. 1). Motor nerve fibers end in an arborization of fine intramuscular twigs ending at the terminal bouton. The motor twigs are myelinated until the very terminus, with a Schwann cell covering all but the synaptic interface. The terminal axon is separated from the motor end-plate region of the muscle fiber by an...

Femoral Neuropathy 61 Anatomy

The femoral nerve is derived from the lumbar plexus, originating from the posterior divisions of the L2, L3, and L4 nerve roots. The nerve provides motor branches to the psoas and iliacus muscles before traveling underneath the inguinal ligament. Subsequently, the nerve divides into motor and sensory branches. Motor branches supply the sartorius, pectineus, and the four heads of the quadriceps muscles. Sensory branches supply sensation to the medial thigh (medial cutaneous nerve of the thigh),...

Recording Electrodes

Recording electrodes used in routine NCS include disc electrodes, ring electrodes, and bar electrodes that connect two discs at a fixed distance. Disc electrodes are commonly used to record motor potentials and nondigital sensory potentials. The discs are connected to separate wires that allow the distance between the active and reference electrode to be altered. Standard interelectrode distance is 3 to 4 cm, but there are occasions when adjustments must be made because of anatomic or...

Action Potential

For a neuron to transmit information, it must generate an electrical current, termed an action potential. Development of the action potential requires an electrical or chemical stimulus, which alters ion flow into the cell. The electrical current that flows into and out of the cell is carried by ions, both positively charged (cations) and negatively charged (anions). The direction of current flow is conventionally defined as the direction of net movement of positive charge. Cations move in the...

Patient Health Information Of Nerve Conduction Studies And Eletromyography

Electrophysiological testing serves a critical role in the evaluation of polyneuropathies (PNs). In conjunction with the information obtained from the neurological history and examination, electrophysiology can be used to assist in isolating a specific diagnosis. Testing can (1) help identify whether the PN involves sensory or motor fibers (2) determine whether the underlying pathophysiology is predominantly demyelinating, axonal, or mixed (demyelinat-ing and axonal) (3) establish duration and...

Virtual Cathode

A tenet of NCS is that depolarization occurs directly under the cathode of the stimulator but, with overzealous attempts to maximize the amplitude of potentials, excess current traveling in the overlying superficial tissues may result in depolarization distal to the cathode. When this occurs, the cathode is virtually in a different place than its actual anatomic location. This can be readily observed by keeping the stimulator in place and increasing the intensity beyond maximal values (see Fig....

Nithi S Anand and David Chad

The myopathic disorders represent a heterogeneous group of diseases with a variety of causes. Although electrodiagnostic testing rarely allows an entirely specific diagnosis to be made, such testing can be extremely helpful in first confirming the presence of myopathy and therefore helping to appropriately categorize it. Standard motor nerve conduction studies generally do not demonstrate substantial abnormalities, except occasional reductions in compound motor potential amplitude in severe...

Sleep Deprivation

Background and Clinical Significance The association of epileptic seizures and sleep has been recognized since at least the 19th century. Gowers, as cited by Chokroverty, found that 21 of patients had seizures exclusively during the night, especially during transitions into and out of sleep, as well as 1 to 2 h after Fig. 3. Photoconvulsive response in an 11-yr-old girl with spells of unresponsiveness, aggravated by bright lights. Fig. 3. Photoconvulsive response in an 11-yr-old girl with...

Review Questions Choose The Best Answer From The Alternatives

During depolarization of the cell membrane, the movement of sodium ions from the ECF into the ICF uses which of the following physiological mechanisms B. Active transport through voltage-gated sodium channel. D. Passive transport through voltage-gated sodium channel. 2. The potential difference across the cell membrane on the inside of the cell is A. Positive at the peak of sodium influx during an action potential. B. Negative at the peak of sodium influx during an action potential. C. Positive...

Response To Intermittent Photic Stimulation

Photomyogenic Response

Similar to hyperventilation, intermittent photic stimulation is performed to activate the EEG. Photic stimulation is performed by using a commercial stroboscopic stimulator placed approx 1 m from the patient's eyes. They are asked to keep their eyes closed and look straight ahead while the ambient room lighting is turned down. The test is performed by alternating flashes varying from 1 to 35 Hz and lasting for 10 s and interrupted by 10 to 30 s with no stimulation. The variables that need to be...

Conclusion

We reviewed the most common entrapment neuropathies that practicing neurologists are likely to see in clinical practice. A good history, physical examination, and neurological examination are essential to guiding one's diagnostic evaluation, and ultimately, in assessing each patient's prognosis and treatment options. Electrodiagnostic Protocol to Evaluate for Tarsal Tunnel Syndrome A. Peroneal motor study stimulating at the ankle, below recording from the extensor digitorum brevis muscle A....

Measurement Of Motor Potentials In

The active electrode is placed over the motor point of the muscle, where the majority of the motor axons synapse with the end plates of the muscle fibers. Rather than measuring a compound nerve action potential, the summation of the muscle fiber action potentials is measured. This is called the compound motor action potential (CMAP) (Fig. 2). In this case, there is no leading edge of a dipole to cause an initial downward deflection, because the depolarization initiates directly beneath the...

Emg

Lamert Eaton Inkrement

The first described clinical neurophysiological abnormality in MG was by Harvey and Masland in 1941, when they reported variability in motor unit potential (MUP) amplitudes. The defect in MG is widespread but not universal individual motor end plates are affected to varying degrees, even within the same motor unit. Some NMJs may be nonfunctional, some may have marginal safety factors, and others may be healthy. Because of this variable involvement, during muscle contraction, NMT may fail at a...

Lambda And Lambdoids 31 Lambda

Lambda waves are sharp monophasic or biphasic waveforms that resemble the Greek letter lambda. They have a duration of 160 to 250 ms, an amplitude of 20 to 50 V, and usually appear over bi-occipital leads, although occasionally may be unilateral (Fig. 7). Lambda waves depend on rapid saccadic eye movements with eyes open. This variant pattern is usually generated when the patient scans a complex patterned design in a well-illuminated room, for instance, dotted ceiling tiles in the laboratory....

Electrodiagnosis

Sensory Nerve Conduction Studies Sensory nerve conduction study (SNCS) results are nearly always normal in radiculopathy as well as MND. The sensory nerve action potential (SNAP) amplitude is normal even when patients have clinical sensory loss because the lesion occurs proximal to the DRG (i.e., is preganglionic) and the peripheral sensory axons are intact. This is the most useful piece of information for differentiating radiculopathies from lesions involving the plexus or individual...

Putting It All Together

Myopathic Units Emg

Now that we have an understanding of the muscle physiology in myopathy and its electrical correlates, it is time to make the final diagnosis. Again, as we mentioned in Section 1., EMG is Electrodiagnostic Clues to the Diagnosis of Specific Myopathies Myopathies that may present with normal EMG Metabolic myopathies Endocrine myopathies Hypokalemic periodic paralysis (in between attacks) Myopathy with fiber type disproportion Myopathies that may present with fibrillation potentials only...

And Nanon E Winslow

Various procedures are commonly used in the recording of the EEG in an effort to increase the diagnostic yield of the test. Common methods, such as hyperventilation (HV), photic stimulation, and sleep deprivation, referred to collectively as activation techniques, are traditionally used toward this end. Less common techniques, such as withdrawal of antiepileptic medications, use of specific triggers reported by the patient, and other idiosyncratic methods can be tried as well. This chapter will...

Limitations And Finer Aspects Of Needle

Needle EMG, although providing valuable insights into a patient's peripheral pathology, has a number of limitations that are important to identify. Similarly, these limitations go hand-in-hand with several often misunderstood aspects of the procedure. 9.1. Needle Placement and MUP Morphology Whereas we would like to think of an individual MUP as the electrical signal of a single motor unit, in fact, a single MUP is actually the electrical signature of a single motor unit as recorded by a needle...

Common Referrals To The Pediatric Emg Laboratory

Deciding whether to request or perform an EMG in a particular case is sometimes difficult, because the number of available diagnostic modalities has increased dramatically in recent years. Genetic testing is available for many neuropathies and muscular dystrophies, and may make EMG unnecessary in certain patients. However, there are many children with acquired conditions and unusual presentations of inherited disorders in whom EMG is an essential test, and the volume of EMG referrals, in our...

Anatomy Histology

Motor Unit Action Potential Muap

Muscle fibers in adults are approx 50 m in size. They are polygonal in shape and are bundled into fascicles (Fig. 1). Each fascicle contains approx 20 to 60 muscle fibers, and each Fig. 1. Schematic diagram of the connective tissue sheaths of muscle. Muscle fibers are bundled into fascicles bordered by perimysial connective tissue. From DeGirolami and Smith, 1982 with permission. Fig. 1. Schematic diagram of the connective tissue sheaths of muscle. Muscle fibers are bundled into fascicles...

Working Model Of Volume Conduction

There are two basic models that have been used to explain the observed phenomena of volume conduction. The first involves the use of a waveform moving down a nerve sitting in a medium. The second relies upon the concepts of what is called solid-angle geometry. Although both models are relatively straightforward, because our goal here is merely to provide a basic understanding of volume conduction, we will omit the discussion on the solidangle geometry model, which can be obtained in the...

Reflex

H stands for Hoffman, after the investigator who first recorded the late response in 1918. The H-reflex is often said to be the NCS parallel of the clinical ankle tendon reflex, but the two tests are probably not evaluating the exact same group of nerve fibers. The tibial nerve is stimulated in the popliteal fossa, with the cathode proximal to the anode, and the response is recorded with the active electrode overlying the belly of the soleus muscle and the reference electrode placed at the...

The Resting Membrane Potential

We have seen in the preceding paragraphs that the net diffusion of ions occurs down the concentration and electrical gradients. If a membrane were completely and equally permeable to all particles, diffusion would be allowed to proceed unchecked, and the various concentration differences across the cell membrane would eventually become equalized. However, in biological systems, both active transport and selective membrane permeability prevent such equalization. The resting membrane potential...

Important Findings In The Pediatric Emg Laboratory

Because of the development of the polio vaccine, SMA has become the dominant anterior horn cell disease affecting children in developed countries. The onset of the most common variant, type I (Werdnig-Hoffman disease), is typically in the first 6 mo of life. The infants present with hypotonia, weakness, and delayed motor milestones. Mothers may report decreased fetal movements. Examination is notable for areflexia or hyporeflexia, hypotonia, weakness, and preserved extraocular movements. Tongue...

Periodic Epileptiform Discharges 41 Introduction

Sharp Waves Eeg

Periodic discharges, as their name implies, are those that recur at regular intervals. In general, the term is used to refer to discharges that appear on the order of every second to every Fig. 13. Rhythmic theta. This tracing is from a 54-yr-old woman with refractory right temporal lobe epilepsy. This depicts an evolving electrographic seizure involving rhythmic and sharply contoured theta activity over right temporal channels, acquired during a complex partial seizure recorded during...

Other Methods

Additional idiosyncratic activation methods may be justified in patients with reflex epilepsy associated with specific stimuli or activities, such as reading or listening to specific music. Patients with psychogenic nonepileptic seizures may perceive similar relationships, and appropriate methods may also induce these spells and establish the correct diagnosis. The importance of making a definitive diagnosis of epilepsy cannot be overstated. Although extended recording on either an ambulatory...

James B Caress Gregory J Esper and Seward B Rutkove

The methodology for performing standard nerve conduction studies has been established by identifying the most helpful and consistent physiological data obtainable while being constrained by a variety of technical and practical limitations. Nerve stimulation occurs underneath the negatively charged anode of the applied stimulator and simultaneous hyperpolarization of the nerve occurs beneath the positively charged cathode. Referential or bipolar recording techniques are used for all types of...

Stage Ii

Sleep Record Form

This stage's onset is identified by the appearance of spindles. They are frontal-centrally predominant waves that occur as a cluster lasting for one to several seconds in duration. The spindle frequency is between 11 and 15 Hz and, in healthy adults, they are bilateral and synchronous in their appearance, with an amplitude up to 30 V. Spindles may appear by themselves or following a vertex wave. In that latter situation, the wave is called a K complex (Fig. 5). Vertex waves are increasingly...

Beta Activity

Beta activity (> 13 Hz) is defined by three relatively distinct frequency bands 18 to 25 Hz activity, which is the most frequently encountered 14 to 17 Hz activity, which is less common and the still rarer, greater than 25 Hz activity. The first two frequencies are seen commonly over the frontal regions and become more prominent as the subject gets drowsy. These two beta rhythms are usually of low voltage (< 25 V). It can be markedly increased by the use of some drugs, most notably the...

Generalized Slowing

Discharge With Phase Reversal Eeg

In discussing generalized slowing of the EEG, several qualifiers must be mentioned. Is the slowing intermittent or continuous Is it rhythmic-monomorphic or arrhythmic-polymorphic In what context does it occur For example, a buildup of generalized slowing during hyperventilation is a normal finding in children, adolescents, and young adults. Finally, some special examples will be considered. Intermittent rhythmic delta activity (IRDA) tends to be monomorphic and is a commonly observed EEG...

Jean K Matheson Randip Singh and Andreja Packard

The classification of sleep disorders is based both on clinical and neurophysiological criteria and is undergoing constant refinement. Sleep disorders can be caused by either a primary disorder of a mechanism controlling sleep or inadequate function of an end organ, such as the upper airways and lungs. Understanding the physiology and pattern of normal sleep is an important foundation for interpreting the clinical symptoms, signs, and neurophysiological abnormalities observed in patients with...

Volume Conduction And Its Role In Specific Tests

Sensory Nerve Conduction Studies Let us begin our discussion by looking at a standard antidromic median sensory study recording from digit 3, a form of bipolar study, in that both E1 and E2 are in proximity to the potential generators (the digital nerves of the middle finger). Figure 3A shows the standard recorded response. Note that there is an initial negativity and a final positivity. In Fig. 3B, the reference electrode is moved to digit 5, essentially changing the biopolar arrangement...

Summary Of Edx Findings In

Nerve Conduction Studies SNCSs normal. MNCS reduced CMAP amplitudes may be observed in muscles experiencing severe axonal loss. In less-involved muscles, CMAP amplitudes may be normal. Ongoing denervation and chronic reinnervation are present in varying degrees in different areas, reflecting abnormalities in multiple nerve and root distributions. The presence of fasciculation potentials should be sought although they are characteristic of the disorder, fasciculation potentials may be...

Physiological Basis Of The

Polarity Eeg

The EEG represents a set of field potentials recorded by multiple electrodes on the surface of the scalp. The electrical activity of the EEG is an attenuated measure of the extracellular current flow from the summated activity of many neurons. The surface EEG predominately reflects the activity of cortical neurons close to the EEG electrodes. Deeper structures, such as the hippocampus, thalamus, or brainstem, do not contribute directly to the surface EEG. However, transmission of electrical...

Photic Stimulation

Photic stimulation is performed in most EEG laboratories for nearly all patients referred for routine EEG. The earliest roots of this activation procedure may be traced back at least to ancient Greece, where descriptions of the potter's wheel to screen people who might have seizures were documented. Bright lights were noted to cause epileptic seizures at the turn of the 20th century. Intermittent photic stimulation IPS with a constant light source was used by 1934, and activation of epileptic...

Anodal Block

When depolarization under the cathode occurs, there is also hyperpolarization of the nerve beneath the anode. The hyperpolarization is without significance in NCS unless the cathode and anode are inadvertently reversed. When this happens, depolarization occurs 2 to 3 cm proximal to the point that has been marked for depolarization, resulting in apparent prolonged Fig. 1. Virtual cathode. From top to bottom, the first waveform shows a slightly submaximal motor response. The second stimulus...

Brachial Plexopathy

Brachial Plexus Neuropathy

The brachial plexus is formed from the ventral roots of C5 through T1 Fig. 1 . It has three trunks upper, middle, and lower , three cords medial, lateral, and posterior , and a number of From The Clinical Neuropysiology Primer Edited by A. S. Blum and S. B. Rutkove Humana Press Inc., Totowa, NJ Fig. 1. Anatomy of the brachial plexus, showing the eventual destinations of all root components. Ext, external extn, extension. Fig. 1. Anatomy of the brachial plexus, showing the eventual destinations...

Clinical Assessment Of Sleep Disorders

A sleep disorder generally occurs for one of two reasons. It may represent a primary disorder of a mechanism controlling sleep or failure of a specific end organ, such as the upper airways and lungs. As in all of clinical medicine, testing must be ordered and interpreted within the context of the patient's clinical presentation, with a clear understanding of the questions to be answered and the inherent limitations of the study proposed. Most patients present with complaints of excessive...

Emg In Selected Myopathies

Before concluding, we highlight a few important features and EMG caveats of some important groups of muscle diseases. Inflammatory myopathies are important because some are eminently treatable. EMG plays a critical role not only in their diagnosis but also for monitoring the activity of the disease and its response to treatment. Although IBM is not responsive to immunosuppressive therapies, unlike polymyositis and dermatomyositis, it is considered here because it may simulate motor neuron...

Membrane Action Potentials

Hodgkin Huxley Channel

Nerve and muscle action potentials occur as a result of sudden changes in permeability of specific ion channels, in response to local perturbations in the voltage of membrane potential. The channels involved are known to be voltage dependent that is, permeability changes are dependent on changes in membrane potentials. Although voltage-dependent ion channels depend on changes in membrane potential to initiate permeability changes, once those changes occur, they revert back to baseline...

Waves

Nerve Conduction Study Tibial Nerve

The F stands for foot, because these responses were first recorded from intrinsic foot muscles. On stimulation of a single motor axon, the wave of depolarization will travel distally to be recorded as part of the CMAP, or M-wave, but also will travel proximally to its anterior horn cell AHC . Retrograde depolarization of AHCs will result in regeneration of an action potential at the axon hillock in a small subset of neurons 5-10 , which then travels back down the motor axon to the innervated...

Epileptiform Variant Patterns

Epileptiform Discharge

There are 4 major types of epileptiform variant patterns 1. 14- and 6-Hz positive bursts. 2. Small sharp spikes benign epileptiform transients of sleep BETS . 3. 6-Hz spike and wave phantom spike and wave . 2.1. Fourteen- and 6-Hz Positive Bursts Previously called 14- and 6-Hz positive spikes or ctenoids, these variants occur as bursts of rhythmic arched waves, similar to sleep spindles, with a smooth negative component and a spike-like positive component Fig. 4 . As the name implies, these...

Brain Death

Alpha Coma Eeg

Brain death is a clinical diagnosis made when there is no evidence of brainstem function on successive neurological exams. Protocols for declaring brain death vary among institutions and according to the age of the patient. The EEG is one of several tests that can help confirm the diagnosis. Complete absence of brain-derived rhythms, ECI Fig. 8 , can help confirm the clinical diagnosis of brain death. Electrocardiogram and respirator derived artifacts are often all that Fig. 6. Burst...

Peroneal Neuropathy

Peroneal neuropathy is the most common focal neuropathy affecting the lower extremity. It is a common cause of foot drop, and, most often, is compressed at the level of the fibular head. The peroneal nerve fibers are derived from the L4-S1 nerve roots. These fibers travel through the lumbosacral plexus, and continue on through the sciatic nerve. Within the sciatic nerve, fibers of the common peroneal nerve run separately from tibial nerve fibers. The common peroneal nerve first gives off the...

Interictal Epileptiform Abnormalities 21 Spikes and Sharp Waves

Centrotemporal Spikes

Spikes and sharp waves are sharply contoured waveforms that are distinct from the EEG background and usually have a negative polarity Fig. 1 . They can be of any voltage and can occur either singly or in repetitive runs with varying frequencies. They can be focal or generalized in distribution. Spikes, by definition, have a duration shorter than 70 ms, whereas sharp waves have a duration between 70 ms and 200 ms. These discharges classically have an asymmetric appearance, with the initial...

Focal Slowing

Polymorphic Delta Eeg Pattern

Focal slowing in the EEG suggests an underlying abnormality but is of nonspecific etiology. It may reflect structural i.e., tumor or infarct or functional i.e., postictal or migraine abnormalities. There exist two spectra of severity, one pertaining to frequency, with slower rhythms representing more severe lesions, and one pertaining to persistence, with continuous slowing a more significant abnormality than intermittent slowing. An interhemispheric frequency difference of less than 1 Hz is...

Specific Disorders Of The Brachial Plexus

Lumbosacral Plexus Schematic

Brachial plexopathies are most commonly caused by trauma, including closed traction injuries as well as penetrating trauma and dislocation of the humerus. The position of the arm and head is important in determining susceptibility of the brachial plexus structures during a closed injury with the arm down at the side, a force causing excessive shoulder depression will be transmitted to the upper trunk C5-6 roots , whereas with the arm overhead, force applied to the axilla is transmitted to the...

Understanding The Time Course Of Development Of Mup Abnormalities

Myopathic Unit

Let us take a situation in which axonal injury occurs to a nerve such that some, but not all of it, will regrow and eventually reinnervate a muscle it controls. For simplicity, this muscle is normally only innervated by three neurons. Figure 12A shows the initial state with a healthy muscle and nerve, with individual muscle fibers having a checkerboard pattern of innervation from three different motor neurons. Figure 12B shows the injured nerve and the associated denervated muscle shortly after...

Electrodiagnosis Brachial Plexopathies

Motor Nerve Conduction Studies Motor nerve conduction studies MNCS are useful mostly for demonstrating significant axonal loss in motor fibers. However, routine MNCS will be abnormal in plexopathy only if the nerve under study is derived from the involved trunk or cord of the brachial plexus. Thus, routine MNCS of the median and ulnar nerves provide information relevant only to the lower trunk medial cord and C8-T1 nerve roots. Unusual conduction studies may be performed for the evaluation...

Spontaneous Potentials Generated By Motor Neurons 51 Fasciculation Potential

Myokymic Discharges

Fasciculation potentials Fig. 8 result from the spontaneous depolarization of a motor neuron and its associated muscle fibers. The morphology of a fasciculation potential is that of a MUP. Fasciculation potentials are substantially larger than fibrillation potentials, are polyphasic, and fire erratically. Fasciculation potentials will appear only intermittently. In fact, one of the best ways for identifying a fasciculation potential is to simply place the needle into the muscle of interest and...

Summary Of Edx Findings In Radiculopathy

Sensory usually normal even if clinical sensory loss is present, an important differentiating feature from nerve and plexus lesions. Care should be taken to record from clinically relevant sensory nerves and to compare with the contralateral side if appropriate. 2. Motor usually normal even in the presence of weakness. CMAP may be decreased with lesions causing severe axon loss, particularly if multiple, adjacent nerve roots are affected. Overall, needle EMG is the most useful EDX test for...

Normal Variant Patterns

Slow Alpha Variant

Phantom Spike Wave Six Per Second Spike Wave Complex This pattern looks like a miniature version of the typical three per second spike wave of typical absence. The spike component is often unimpressive hence, the phantom spike designation . Although it may be diffuse, at times the distribution of this phenomenon and the state in which it occurs allow discrimination of two forms. It occurs in waking, at relatively higher amplitude and the anterior head regions in male subjects Fig. 28 ,...

Basis Of Brain Electrical Activity 21 Membrane Polarity

Diffusion Electrical Gradient

All neurons and glia have lipid bilayer membranes separating the delicate internal machinery of the cell from the external environment. The neuronal membrane is an excellent insulator and separates different concentration of ions inside the cell from those outside the cell. The activity of ion channels is fundamental to signaling in the nervous system. The movement of ions that carry electrical charge through ion channels results in voltage changes across the membrane. Electrical potentials are...

Median Motor Response

Pictures Nerve Conduction Studies

Needle EMG in the evaluation of PN is helpful for several reasons. First, needle examination of lower extremity muscles can assist in establishing the presence of motor axonal injury by identifying the presence of a gradient of abnormality. In this situation, the distal muscles e.g., extensor hallucis longs are most severely affected, with proximal muscles e.g., tibialis anterior and gastrocnemius showing more minor changes, and muscles that are even more proximal e.g., vastus lateralis...

Specific Epileptic Syndromes

Lennox Gastaut Syndrome Lgs Eeg

In contrast to seizure location and the resultant clinical manifestations, differences exist in the occurrence of epileptic syndromes in adult and pediatric epileptology. Most specific epileptic syndromes begin in childhood and may continue into adulthood. We shall start with the benign epileptic syndromes and then the malignant syndromes. Descriptions of the epileptic syndromes come from the ICES. Additional points within each syndrome are specifically referenced. The following specific...

Martin Gruber Anastomosis

Martin Gruber Anastomosis

Peripheral nerve myelination begins at approximately the 15th week of gestation and continues through 3 to 5 yr of age. Therefore, for children younger than the age of 5 yr, special tables are required to evaluate NCS data. In term infants, the latency and conduction velocity values are approximately half those recorded in adults, and premature infants have even slower conduction velocities at the beginning of the third trimester, velocities are one-third of those measured in term infants. NCS...

Conduction Studies 21 Facial Nerve

Schematic Diagram Trigeminal Nerve

Of all cranial nerves, the facial nerve Fig. 1 is the one most frequently studied in EMG labs. It emerges from the pons, coursing across the cerebello-pontine angle to the internal From The Clinical Neurophysiology Primer Edited by A. S. Blum and S. B. Rutkove Humana Press Inc., Totowa, NJ Fig. 1. Major branches of the facial nerve and muscles that they innervate. Fig. 1. Major branches of the facial nerve and muscles that they innervate. acoustic meatus, where it enters the facial canal in the...

Radial Neuropathy 41 Anatomy

The radial nerve receives fibers from all three trunks of the brachial plexus C5-T1 roots . The posterior divisions of the three trunks unite to form the posterior cord, which gives off the radial nerve. The radial nerve exits the lateral wall of the axilla, and travels distally through the proximal arm, just medial to the humerus. Proximally, three sensory nerves the posterior cutaneous nerve of the arm, the lower lateral cutaneous nerve of the arm, and the posterior cutaneous nerve of the...

Neonatal Period

Encoche Frontales

The patterns observed in the neonatal EEG and the significance attributed to them depends on the conceptional maturity of the infant. Therefore, to evaluate the neonatal EEG, the reader must know the conceptional age of the infant duration in weeks since last menstrual period beginning of pregnancy , in addition to the postnatal age. Patterns observed also depend on the infant's state of arousal, and this should also be noted. The EEG patterns are evaluated in light of these conditions. The...

Hyperventilation 21 Background

Symmetric Photic Driving Response

Activation of seizures by HV was first reported in 1924, even before the discovery of the EEG. This technique became widely used in the diagnosis of absence seizures. HV responses can vary widely depending on age of patient and the amount of individual effort put forth. Common HV From The Clinical Neurophysiology Primer Edited by A. S. Blum and S. B. Rutkove Humana Press Inc., Totowa, NJ Fig. 1. A Start hyperventilation HV in an adult. Continued Fig. 1. A Start hyperventilation HV in an adult....

Myopathic Muscle Histopathology And The Origin Of Abnormal Electrical Activity Detected By

Chronic Muscle Disease

Myopathic states result in a variety of structural alterations in the muscle. Muscle fiber atrophy is typically produced by denervation, although it can be observed in the late stages of severe myopathies Fig. 8 . Muscle fiber hypertrophy Fig. 8 is observed in chronic muscle diseases, notably in the muscular dystrophies and in other longstanding disorders e.g., hypothyroid myopathy . Muscle fiber necrosis results in disruption and fragmentation Fig. 8. Chronic myopathic changes Emery-Dreifuss...

Differential Diagnosis Of Pns

Pure motor PNs are uncommon in fact, many have some sensory component , and can be axonal or demyelinating in nature. One example of an acute axonal motor PN is the axonal form of GBS, or acute motor axonal neuropathy. Lead neuropathy can occur acutely or chronically, and is predominantly motor in nature. Multifocal motor neuropathy with conduction block is a chronic and demyelinating neuropathy that is often associated with high ganglioside GM1 antibody titers, but generally presents as...

Basic Mup Parameters 71 Duration

The duration of the motor unit is perhaps its most important characteristic Fig. 11 . The duration reflects how dispersed the motor unit is in time and space and is the least affected by proximity of the needle electrode to the motor unit being recorded. Generally, short-duration motor units are commonly observed in myopathic conditions, whereas long-duration motor units are observed in neurogenic disorders. In any muscle, motor unit size will vary within a distribution of durations however,...

Rhythmic Variant Patterns

Rhythm Eeg

There are six main types of rhythmic variant EEG patterns 3. Rhythmic temporal theta burst of drowsiness psychomotor variant . 4. Subclinical rhythmic electrographic theta discharges in adults SREDA . 6. Frontal arousal rhythm FAR . This pattern was described first by Goodwin in 1947. There are two types of alpha variants, slow and fast. The slow subharmonic alpha variant appears as an abrupt rhythm usually at half the frequency of the patient's more typical waking background rhythm, and often...

Kevin R Scott and Milind J Kothari

Nerves of both the upper and lower extremities are frequently injured for a variety of reasons. In the arms, median neuropathy at the wrist is by far the most common disorder ulnar neuropathy also occurs with a relatively high frequency. Other mononeuropathies affecting the upper extremities, including anterior and posterior interosseous neuropathies, and musculocutaneous neuropathies, are very infrequent. In the legs, peroneal neuropathy at the fibular neck and lateral femoral cutaneous...

Spontaneous Potentials Generated By Single Muscle Fibers 41 Fibrillation Potentials

Complex Repetitive Discharges

A fibrillation potential represents the electrical activity generated by the depolarization of a single muscle fiber and is depicted in Fig. 3. These potentials are typically triphasic, with an initial small positivity, followed by a large negative spike, and ending with another small positive spike. Generally, these potentials are thought of as being recorded by the needle electrode a short distance from the spontaneously depolarizing muscle fiber. The triphasic morphology of this potential is...

Electrodiagnosis Lumbosacral Plexopathies

Several principles of electrodiagnosis in lumbosacral plexopathy are similar to those described in the evaluation of brachial plexus lesions. The anatomy of the lumbosacral plexus is more straightforward again, considering lumbar and sacral plexus separately is helpful. In general, lesions tend to affect either one but rarely both the lumbar and sacral plexus. In cases of lumbar plexopathy, the patient generally presents with quadriceps weakness and the differential diagnostic considerations...