**4. Conclusion**

cerebral peduncle [82,84]. The goal is an aggressive resection of such lesions to the greatest extent as possible, to improve the patient's survival chance and the postoperative life quality. With this aim, monopolar or bipolar stimulation of cortical and subcortical areas is applied carefully. Visual detection of the elicited movement of the limb contralateral to the operative side is usually employed during the mapping of motor areas. However, it is difficult to detect visually a subtle twitch over an entire contralateral limb at once, specially during awake surgery (because of the specific patient positioning). EMG recording is more sensitive than the visual detection of muscle twitch. EMG signals precede the visually observed motor activity, since the applied stimulation may weakly activate motor pathways enough to elicit EMG responses and yet not recruit a sufficiently large pool of motor neurons to produce visible muscle movement. Moreover, multichannel EMG recording has three important advantages: First, it facilitates the monitoring of the face, upper and lower extremities simultaneously, detecting motor responses that may not be observed during gross inspection (Fig.10). This advantage is particularly important during mapping of subcortical pathways. Second, EMG recording also improves the ability to detect subclinical ictal events (EMG activity elicited by stimulation that persists after the end of the stimulation). In addition, EMG—complementary to electrocorticography— allows the early detection of spreading muscle activation over a limb as a sign of seizure. The immediate removal of stimulation diminishes the likelihood of the progression of a seizure. Third, the sensitivity of EMG recording allows the application of

14 Electrodiagnosis in New Frontiers of Clinical Research

lower intensity and duration of stimuli during mapping procedures [85-87].

**Figure 10.** Multichannel EMG recording during mapping for glioma surgery. Stimuli artifact. ( ) Muscle activity

( ) recorded preceding visual muscle twitch ( ).

Virtually all primary neuromuscular diseases result in changes in the electric activity recorded from the muscle fibers. The pattern of abnormalities can usually mark the underlying pathol‐ ogy as neuropathic (e.g. disorders affecting the CNS, nerve roots, plexuses and peripheral nerves), myopathic, or NMJ disorder, etc. EMG recording allows measurement of the severity of the injury, and provides prognostic information.

In the field of intraoperative neuromonitoring, to date, EMG recording – despite its low specificity - continues to be a valuable tool included in a multimodal monitoring set during diverse neurosurgical and orthopedic procedures.
