**2.1. Needle EMG (nEMG)**

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

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].

**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

Overview of the Application of EMG Recording in the Diagnosis and Approach of Neurological Disorders

http://dx.doi.org/10.5772/56030

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*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:

progressing motor neuron disease and chronic myositis [14].

myelinated fibers in early reinnervation stage [15].

with abnormal morphology can be recorded in neuromuscular disorders:

**•** Short-duration MUAPs are often detected in disorders with loss of muscle fibers [11].

**•** Long-duration MUAPs are typically found in chronic neuropathic disorders and polymyo‐

**•** A mixed pattern (coexisting MUAPs of long and short duration) can be observed in rapidly

*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

**•** An abnormally increased polyphasia is a non-specific signal of both myopathic and

**•** Satellite potentials are observed in subacute processes and result from denervated muscle fibers that are reinervated by collateral sprouts from adjacent unmyelinated or thinly

short duration, small amplitude and also polyphasic.

sitis [12,13].

neuropathic disorders [2,12].
