**3. EMG study**

## **3.1. Muscle voluntary contraction recording**

In depolarization, the summation of action potentials of the MUs (MUAPs) can be assessed by analysis of their parameters (fig. 1).

Overview of the Application of EMG Recording in the Diagnosis and Approach of Neurological Disorders http://dx.doi.org/10.5772/56030 3

**2. EMG recording techniques**

2 Electrodiagnosis in New Frontiers of Clinical Research

**2.1. Needle EMG (nEMG)**

**2.2. Surface EMG (sEMG)**

**3. EMG study**

**3.1. Muscle voluntary contraction recording**

analysis of their parameters (fig. 1).

EMG devices record the electrophysiological activity of MUs. EMG recordings can be per‐

nEMG permits local recording from deep muscles by means of insertion of a needle electrode into the muscle tissue. The needle insertion point is located by identifying anatomic landmarks which may be confirmed through the proper contraction of the selected muscle. nEMG can be used to assess individual MUs and has greater sensitivity and accuracy in the recording of

However, nEMG has several limitations. First, it reflects the activity of only a small number of active MUs whose fibers are close to the position of the detection site (not representative of all the fibers in the MU, due to its small detection volume). An adequate sample is needed to ensure adequate power (sensitivity and specificity) of the analysis of MUAPs. Moreover, standard sample size is difficult in exploring small muscles [5]. Second, nEMG is painful especially during muscle activation, and prolonged nEMG recording is not possible. In rare cases, local trauma (e.g., pneumothorax) could occur during the examination of some delicate regions [6]. Furthermore, nEMG is time and temperature sensitive. In this regard, the detected signal in nEMG may vary as a function elapsed time from the onset of the nerve injury [7]. Since the temperature exerts a profound influence on neuromuscular transmission and propagation of the action potential along the muscle fibers, a low temperature at the exami‐

nation area modifies the parameters and characteristics of the recorded signals [8].

resistance subsequently disturb the sEMG signal (e.g. obesity and edema).

sEMG is a technique to measure muscle activity noninvasively using surface electrodes placed on the skin overlying the muscle, and has several advantages. First, sEMG recording is pain‐ less, especially when used in the absence of peripheral nerve stimulation. Furthermore, sEMG electrodes record from a wide area of muscle territory providing a more global view of MUs. Finally, it allows prolonged simultaneous recordings of muscle activity from multiple sites. However, sEMG has a relatively low-signal resolution, is highly susceptible to movement artifacts [9] and body temperature. In addition, sEMG signals are dominated by the contribu‐ tions of superficial MUs, while deeper MUs are not assessed; conditions that increase skin

In depolarization, the summation of action potentials of the MUs (MUAPs) can be assessed by

formed by means of intramuscular (needle) or non-invasive (surface) electrodes.

high-frequency signals such as different types of spontaneous activity [4].

**Figure 1.** Morphology and parameters of a motor unit action potential (MUAP) measured during nEMG recording. A. A normal MUAP with three phases. B. A polyphasic, high amplitude and enlarged MUAP recorded in chronic neuropa‐ thy with reinnervation. C. In some myopathic and neuromuscular junctions (NMJ) disorders, the resulted MUAPs are of short duration, small amplitude and also polyphasic.

*Duration* is measured from the initial deflection from baseline to the terminal deflection back to baseline; it reflexes the synchrony and also the muscle fiber density in an MU. The average duration of MUAPs increases from infancy to adult (related to the increased width of the endplate zone), and even more during old age; the percentage depends on the specific muscle [2,10]. Abnormalities of MUAP duration can be shown in pathological conditions:


*Morphology* (number of phases) is defined as the number of baseline crossings of an MUAP and reflects the firing synchrony of the muscle fibers within an MU. Normally, an MUAP has two to four phases. A MUAP of more than four phases is named polyphasic potential. MUAPs with abnormal morphology can be recorded in neuromuscular disorders:


*Stability* of the firing of all muscle fibers of the MU reflects the effective transmission across the neuromuscular junctions (NMJs) corresponding to each generated action potential. Abnormalities on MUAP stability indicate increased variability of an MUAP, either in its amplitude, morphology or both; this finding can be shown in primary disorders of the NMJ (e.g., myasthenia gravis, Lambert-Eaton syndrome); as well as often being observed as secondary phenomena in neuropathic (e.g., early reinnervation) or myopathic disorders.

*Activation* is a measurement of the ability to increase firing rate. It depends on the effort exerted by the patient and the examined muscle (e.g. gastrocnemius muscle has some difficulty in its activation). This is a central process [21]. Poor activation may be seen in diseases of the central nervoussystem(CNS)orasamanifestationofprovokedpain(poorcollaborationduringnEMG).

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At resting state, muscle activity can be recorded using either intramuscular (needle) or noninvasive (surface) detection systems. The difference between these two detection modalities is based on the volume conductor that separates the muscle fibers from the recording electrodes.

In a healthy muscle at rest, spontaneous physiological activity can be recorded by means of

**•** End-plate potentials: result from the synchronization of miniature end-plate potentials, and

**•** Insertional activity: induced by mechanical depolarization of muscle fiber due to needle

Abnormal spontaneous activity provides information about the topography, diagnosis, time course (spontaneous activity is detected in acute and sub-acute stages of the nerve lesion) and also about the severity in neurogenic, myopathic and NMJ disorders [14,23,24] (fig. 3).

**•** Fibrillation potentials, positive sharp waves, complex repetitive and myotonic discharges resulting from single denervated muscle fibers with an unstable membrane potential that

**•** Fasciculation, neuromyotonic and myokymic discharges generating from disturbance of a

**3.2. Resting state recording**

electrode insertion (fig 3).

group of muscle fibers.

can be recorded near the end-plate zone.

The most described abnormal spontaneous activities include:

fire individually without axonal stimulation.

**Figure 3.** Some examples of spontaneous activity (nEMG recording).

nEMG:

A special technique called "single fiber EMG (SFEMG)" allows assessment of the abnormalities in the physiological variation of transmission time in the motor end-plate, and in the propa‐ gation velocity along the muscle and nerve fibers. This method is based on obtaining a single muscle fiber action potential by means of a special electrode with a small recording area. SFEMG is the most sensitive test to demonstrate an impaired neuromuscular transmission in myasthenia gravis. However, this technique is not specific in differentiating between myopa‐ thies and neuropathies, or between pre- and postsynaptic NMJ disorders [16-18].

*Amplitude* is commonly measured from peak to peak. It is proportional to the distance from the recording electrode to the muscle fiber, reflecting only those few depolarized fibers nearest to the recording electrode [19]. The progressive loss of MUs, unless in some muscle groups as of the seventh decade of life, results in MUAPs of smaller amplitude [20].This phenomenon is especially noticeable in extensor digitorum brevis muscle. An MUAP can show abnormal amplitude in the following conditions:


*Recruitment* refers to the increase of the firing rate from incorporation of additional MUs [21,22]. MUAP recruitment is reduced primarily in neuropathic diseases and rarely in severe end-stage myopathies [12] (fig 2).

**Figure 2.** EMG signals recorded from maximum muscle contraction.

*Activation* is a measurement of the ability to increase firing rate. It depends on the effort exerted by the patient and the examined muscle (e.g. gastrocnemius muscle has some difficulty in its activation). This is a central process [21]. Poor activation may be seen in diseases of the central nervoussystem(CNS)orasamanifestationofprovokedpain(poorcollaborationduringnEMG).

#### **3.2. Resting state recording**

*Stability* of the firing of all muscle fibers of the MU reflects the effective transmission across the neuromuscular junctions (NMJs) corresponding to each generated action potential. Abnormalities on MUAP stability indicate increased variability of an MUAP, either in its amplitude, morphology or both; this finding can be shown in primary disorders of the NMJ (e.g., myasthenia gravis, Lambert-Eaton syndrome); as well as often being observed as secondary phenomena in neuropathic (e.g., early reinnervation) or myopathic disorders.

A special technique called "single fiber EMG (SFEMG)" allows assessment of the abnormalities in the physiological variation of transmission time in the motor end-plate, and in the propa‐ gation velocity along the muscle and nerve fibers. This method is based on obtaining a single muscle fiber action potential by means of a special electrode with a small recording area. SFEMG is the most sensitive test to demonstrate an impaired neuromuscular transmission in myasthenia gravis. However, this technique is not specific in differentiating between myopa‐

*Amplitude* is commonly measured from peak to peak. It is proportional to the distance from the recording electrode to the muscle fiber, reflecting only those few depolarized fibers nearest to the recording electrode [19]. The progressive loss of MUs, unless in some muscle groups as of the seventh decade of life, results in MUAPs of smaller amplitude [20].This phenomenon is especially noticeable in extensor digitorum brevis muscle. An MUAP can show abnormal

**•** In chronic neuropathies, the MUAP amplitude can be increased due to reinnervation process

*Recruitment* refers to the increase of the firing rate from incorporation of additional MUs [21,22]. MUAP recruitment is reduced primarily in neuropathic diseases and rarely in severe

thies and neuropathies, or between pre- and postsynaptic NMJ disorders [16-18].

**•** Reduced amplitude of MUAP is a usual finding in some myopathies.

amplitude in the following conditions:

4 Electrodiagnosis in New Frontiers of Clinical Research

end-stage myopathies [12] (fig 2).

**Figure 2.** EMG signals recorded from maximum muscle contraction.

[12].

At resting state, muscle activity can be recorded using either intramuscular (needle) or noninvasive (surface) detection systems. The difference between these two detection modalities is based on the volume conductor that separates the muscle fibers from the recording electrodes.

In a healthy muscle at rest, spontaneous physiological activity can be recorded by means of nEMG:


Abnormal spontaneous activity provides information about the topography, diagnosis, time course (spontaneous activity is detected in acute and sub-acute stages of the nerve lesion) and also about the severity in neurogenic, myopathic and NMJ disorders [14,23,24] (fig. 3).

The most described abnormal spontaneous activities include:


**Figure 3.** Some examples of spontaneous activity (nEMG recording).

On the other hand, resting sEMG recording is helpful in differentiating several types of tremors, myoclonus, and dystonia. The mean rectified sEMG signal varies linearly with the force generated at constant length and velocity. This linear relationship is maintained even in pathological conditions. sEMG may be used to classify movement disorders through meas‐ urement of frequency and amplitude of MUAPs. This technique can provide information about MU recruitment and synchronization, and also determine the relationship of the involved muscles, whether antagonists discharge simultaneously or alternately to produce some movement disorders [9,25-27] (fig 4).

the samples ("outliers"). Both methods offer different sensitivities. The combination of outliers

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**•** *Count of "turns"*: consists of the number of turns recorded in one second. It generally reflects the number of active MUAPs, their complexity and frequency of discharge. A "turn" was traditionally defined as any amplitude change signal of 100 *u*V [30]. It is important to take in account that a turn may correspond to a peak within an MUAP, an interaction between

**•** *Mean amplitude between turns (A/T)* and the *number of turns divided by the mean amplitude*

**•** *Upper centil amplitude* defines the upper limit of the peak-to-peak amplitude; the spikes with amplitude that exceeds by 1% are identified. This parameter is normal or decreased in some

**•** *Activity parameter* measures the 'fullness' of the interference pattern, and is the sum of the

**•** *Numberofsmallsegments(NSS)*quantifiesthesmallinflexionsofMUAPs,includingthesmallest segmentbetweensubsequentturns.NSSincreaseswiththenumberofMUAPdischarges,but reaches a constant value at higher MUAP discharge rates. This parameter has been shown as

**•** *Spectral analysis (SA)* traditionally consists of a fast Fourier transformation of the EMG signals; the output displays the range and amplitude of the component frequencies. SA is been used extensively in the study of muscle fatigue. The diagnostic value varies according

**•** *Automatic decomposition electromyography* comprises the extraction of MUAPs from EMG interference pattern employing digital filtering; the decomposition and analysis of validated MUAPs. Measured parameters include duration, amplitude, rise time, area, ratio, area/

**•** *Computer-aided MU nerve estimation:* high density multichannel EMG recording provides the spatio-temporal information for MUAPs. This technique allows the assessment of the

Electroneurography (ENG) assesses the function and integrity of peripheral motor nerve structures by means of sEMG recording after electrical stimulation. ENG contributes to localize, typify (axonal or demyelinating nature), and establish the course and the severity of the lesion, and is temperature sensitive [39]. On the other hand, magnetic stimulation is also

a tool for the electrical stimulation of peripheral nerves and spinal roots [40].

increased in myopathic and normal or decreased in neurpathic conditions [30].

myopathies, whereas it is normal or increased in neuropathies [30,32].

*/A)* are indicators for identifying neuropathies and myopathies, and also

and mean values may be the optimal way to detect abnormalities in a sample [28,29].

The principal measurements during a voluntary contraction include:

superimposed MUAPs, as well as background noise.

*between turns (T2*

establishing severity [30,31].

duration of specific segments [30,32].

to different power frequencies [33,34].

number of functioning MUs [38].

amplitude, number of phases, turns and fire rates [35-37].

**3.4. EMG recording in peripheral nerve stimulation**

**Figure 4.** In resting sEMG recording, an alternative movement at 4-5 Hz over extensor (upper trace) and flexor (lower trace) musculature of the wrist is recorded in a patient with a diagnosis of Parkinson´s disease.

#### **3.3. EMG analysis**

The analysis of MUAPs can be performed on a qualitative or quantitative basis. At least 20 samples from each studied muscle is widely accepted as representative [5].

#### *3.3.1. Qualitative analysis*

Visual recognition only provides limited information, detecting alterations in few components of MUAPs. The effectiveness of this method depends on the experience of the performer, as the accuracy in measurements is limited by the presence of background noise and depends on collaboration from the patients. To perform qualitative MUAP analysis, the number of phases of a single MUAP and recruitment during voluntary activity are visually analyzed from the MUAPs.

#### *3.3.2. Semi-quantitative analysis*

The classical method consists of manual measurement of duration, amplitude, and number of phases of individual MUAPs; and then comparison of these data with a set of normal values for the studied muscle and age group.

#### *3.3.3. Quantitative analysis*

The parametric method establishes a comparison between sample mean values and reference intervals (standard deviation), while the nonparametric method considers both extremes of the samples ("outliers"). Both methods offer different sensitivities. The combination of outliers and mean values may be the optimal way to detect abnormalities in a sample [28,29].

The principal measurements during a voluntary contraction include:

On the other hand, resting sEMG recording is helpful in differentiating several types of tremors, myoclonus, and dystonia. The mean rectified sEMG signal varies linearly with the force generated at constant length and velocity. This linear relationship is maintained even in pathological conditions. sEMG may be used to classify movement disorders through meas‐ urement of frequency and amplitude of MUAPs. This technique can provide information about MU recruitment and synchronization, and also determine the relationship of the involved muscles, whether antagonists discharge simultaneously or alternately to produce some

**Figure 4.** In resting sEMG recording, an alternative movement at 4-5 Hz over extensor (upper trace) and flexor (lower

The analysis of MUAPs can be performed on a qualitative or quantitative basis. At least 20

Visual recognition only provides limited information, detecting alterations in few components of MUAPs. The effectiveness of this method depends on the experience of the performer, as the accuracy in measurements is limited by the presence of background noise and depends on collaboration from the patients. To perform qualitative MUAP analysis, the number of phases of a single MUAP and recruitment during voluntary activity are visually analyzed from the

The classical method consists of manual measurement of duration, amplitude, and number of phases of individual MUAPs; and then comparison of these data with a set of normal values

The parametric method establishes a comparison between sample mean values and reference intervals (standard deviation), while the nonparametric method considers both extremes of

trace) musculature of the wrist is recorded in a patient with a diagnosis of Parkinson´s disease.

samples from each studied muscle is widely accepted as representative [5].

movement disorders [9,25-27] (fig 4).

6 Electrodiagnosis in New Frontiers of Clinical Research

**3.3. EMG analysis**

*3.3.1. Qualitative analysis*

*3.3.2. Semi-quantitative analysis*

*3.3.3. Quantitative analysis*

for the studied muscle and age group.

MUAPs.

