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Objective: Intertrial variability (ITV) of motor responses to peripheral (CMAP) and transcranial (MEP) stimulation prevents their use in follow-up studies. Our purpose was to develop strategies to reduce and measure CMAP and MEP ITV to guide long-term monitoring of conduction slowing and conduction failure of peripheral and central motor pathway in the individual patient., Methods: Maximal compound muscle action potentials to High Voltage Electrical Stimulation (HVES) of lumbo-sacral nerve roots (r-CMAP) and activated, averaged motor evoked potentials (MEPs) to Transcranial Magnetic Stimulation (TMS) using double cone coil were recorded from 10 proximal and distal muscle districts of lower limbs. The procedure was repeated twice, 1-2 days apart, in 30 subjects, including healthy volunteers and clinically stable multiple sclerosis patients, using constant stimulating and recording sites and adopting a standardized procedure of voluntary activation. ITV for latency and area indexes and for the ratio between MEP and r-CMAP areas (a-Ratio) was expressed as Relative Intertrial Variation (RIV, 5th-95th percentile). As an inverse correlation between the size of area and ITV was found, raw ITV values were normalized as a function of area to make them comparable with one another., Results: All RIV values for latencies were significantly below the optimum threshold of ± 10%, with the exception of r-CMAP latencies recorded from Vastus Lateralis muscle. RIVs for a-Ratio, the most important index of central conduction failure, ranged from a maximum of -25.3% to +32.2% (Vastus Medialis) to a minimum of -15.0% to + 17.4% (Flexor Hallucis Brevis)., Conclusions: The described procedure represents an effort to lower as much as possible variability of motor responses in serial recording; the reported ITV normative values are the necessary premise to detect significant changes of motor conduction slowing and failure in the individual patient in follow-up studies.

Objective: To develop a neurophysiological method to explore central motor pathways to proximal and distal muscles of lower limbs., Methods: MEPs to transcranial magnetic stimulation using the double cone coil were bilaterally and simultaneously recorded from vastus medialis, tibialis anterior and flexor hallucis brevis. Voluntary facilitation was controlled using a predefined sequence of movements of constant amplitude. Compound motor action potentials elicited by maximal high voltage electrical stimulation of lumbosacral roots (root-CMAPs) were recorded from the same muscles to obtain the corresponding peripheral conduction times. We studied 28 healthy subjects and 28 multiple sclerosis (MS) patients with no or mild motor impairment., Results: The described facilitation procedure and the averaging of 5 MEPs reduced area variability to about 10%. In MS patients conduction slowing and/or MEP area reduction in at least one muscle was found in 91.7% of cases, with significant correlation with individual motor impairment., Conclusions: Combined use of stable MEPs and maximal root-CMAPs was able to detect both conduction slowing and conduction failure in central motor pathways to proximal and distal districts of lower limbs in MS patients., Significance: The proposed method provides an extensive electrophysiological mapping of central motor impairment of lower limbs in clinical application., (Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: To describe a neurophysiological method to locate the optimal stimulation site (OSS) over the vertebral column, customized to the individual subject, to achieve maximal activation of lumbosacral roots by means of non-invasive high voltage electrical stimulation (HVES)., Methods: OSS was located in 30 volunteers by testing different stimulation points of a surface multi-electrode array placed over the dorso-lumbar junction of the vertebral column. The dorso-ventral stimulating montage was used (Troni et al., 1996). Motor responses to root stimulation (rCMAPs) were bilaterally recorded from Vastus Medialis (VM), Tibialis Anterior (TA), Soleus (SL) and Flexor Hallucis Brevis (FHB) muscles. The direct nature of rCMAPs was tested by delivering two maximal stimuli 50 ms apart., Results: Except for a few subjects with large girth, maximal rCMAPs could be obtained from all muscles with a stimulating current intensity up to 550 V (1050 mA). Maximal double HVES excluded any reflex component in the recorded rCMAPs. The procedure was well tolerated and no side effects were observed., Conclusions: A single maximal electric shock delivered at the proper vertebral level by means of the dorso-ventral montage is able to safely achieve synchronous, bilateral maximal activation of several roots, from L3 to S1., Significance: Maximal activation of lumbosacral roots at their origin, unattainable with magnetic stimulation, is the essential requirement for direct detection of proximal nerve conduction slowing and block in lower limbs., (Copyright © 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: To describe a new method of segmental analysis of motor nerve conduction velocity (mCV) in the tibial nerve (Tn) tract distal to the upper margin of the tarsal tunnel (TT)., Methods: Compound muscle action potentials (CMAPs) were recorded with a coaxial needle electrode from the flexor hallucis brevis muscle (FHB), to test the medial plantar nerve (MPn), and from the flexor digiti quinti brevis (FDQB) and the first dorsal interosseous (FDI) muscles, to test the superficial and deep branches of the lateral plantar nerve (sLPn and dLPn, respectively). CMAPs were elicited by stimulating at three sites located above (S1) and below (S2) the TT and at the sole of the foot (S3 for MPn and S4 for LPn)., Results: In 20 normal subjects the mean mCV in the proximal (S1 to S2) tract was 44.5+/-4.7, 43.5+/-5.9 and 42.6+/-4.2m/s for the MPn, sLPn and dLPn, respectively. The corresponding values in the intermediate tract (S1 to S3/S4) were 40.7+/-5.6, 39.4+/-5.6 and 40.9+/-5.8m/s., Conclusions: Segmental analysis of mCV in distal Tn can be performed when CMAPs are recorded using a coaxial needle electrode, which prevents simultaneous recording of activity from nearby muscles groups., Significance: Conventional neurophysiological examination for suspected entrapments in distal Tn usually can not discriminate between a lesion inside the TT or distal to it. The proposed technique, as suggested by the reported results in clinical application, may help to better define the lesion site., (Copyright (c) 2010. Published by Elsevier Ireland Ltd.)

The conduction velocity in the different partial segments of the monosynaptic pathway of the lower limbs has been assessed in 50 unselected diabetic patients in order to evaluate the distribution of conduction slowing in the entire course of peripheral nerves in the most common form of polyneuropathy. According to the method previously described (Troni 1981), the conduction velocity in the entire course (popliteal fossa-to-spinal cord), in the proximal segment (buttock-to-spinal cord) and in the distal segment (pf-to-buttock) of the H pathway, has been determined and expressed by mixed (sensory-motor) conduction indexes. Moreover, the conduction velocity of the 1a afferent and of the motor fibres, has been selectively evaluated in the pf-to-buttock segment. The comparison between the impairment of each partial conduction parameters proves the existence of a clear-cut proximo-distal gradient of conduction slowing in the H pathway in diabetic polyneuropathy. Marked slowing in the larger-diameter 1a afferent fibres can also be demonstrated in the pf-to-buttock segment.

An electrophysiological method is described for evaluating the conduction velocity in the different partial segments of the monosynaptic reflex pathway of the lower limbs in man. Using the latencies of M and H responses recorded from the soleus muscle elicited by stimulating the posterior tibial nerve at the popliteal fossa (pf) and the sciatic nerve at the upper thigh, the conduction velocities in the entire course (pf-to-spinal cord), in the proximal segment (upper thigh-to-spinal cord), and in the distal segment (pf-to-upper thigh) of the H circuit, were evaluated and expressed by mixed (sensory-motor) conduction indexes. The conduction distances were measured by using the Th11 spinal process as a reference point on the vertebral column. The conduction velocity of the 1a spindle afferent fibres and of the motor fibres was selectively determined in the pf-to-buttock segment. The results obtained in 50 healthy subjects are presented and the methodological problems related to the proposed technique are discussed.

Conduction velocity (CV) in the H pathway, expressed by a mixed (sensorimotor) index (HCV), showed a very reduced intra-individual variability when compared to conventional conduction parameters in normal subjects. HCV, tested serially over increasing intervals of time, was about 4 times more stable than motor CV in deep peroneal nerve and about 6 times more stable than the sensory CV in sural nerve. The HCV was so accurate in showing marginal conduction changes that it clearly revealed, in normal persons, a circadian rhythm of conduction velocity, well correlated with circadian variations of body temperature, which totally escaped conventional conduction parameters. owing to its reduced variability, this conduction parameter represents, within the limits in which it can be reliably used in clinical application, a first choice tool for longitudinal conduction studies.

When muscle fibers are stimulated in the distal portion of the human biceps brachii, far enough from the end-plate region, a discrete single fiber activity can be picked up proximally by means of a selective recording electrode. The distally evoked potentials show a linear relationship between latency and distance and can be recorded also in curarized patients. The risk of stimulating the intramuscular nerve endings is remote and, when it occasionally happens, the indirectly evoked muscle activity can be distinguished from the direct one. As direct muscle stimulation is feasible and safe, propagation velocity along single fibers can be determined in situ over a long distance. The results obtained in 50 normal subjects are presented.

Measurement of conduction velocity along the H reflex arc was used to study sensorimotor peripheral nerve function in diabetic patients during short- and long-term improvement of hyperglycemia. In ten type I diabetics a slight (p less than 0.05) conduction increase occurred after 6 hours of normal glycemia induced by an artificial endocrine pancreas. Similar but more prominent improvement occurred in twelve type I diabetics treated with continuous subcutaneous insulin injection for 6 months. The results suggest that nerve conduction slowing in diabetic patients stems partly from reversible, nonstructural abnormalities and partly from more slowly reversible morphological or chemical changes in peripheral nerve.

We investigated the Intertrial Variability and Relative Intertrial Variation (RIV) of latency and area of motor responses to High Voltage Electric Stimulation (HVES) of lumbo-sacral roots and to Transcranial Magnetic Stimulation (TMS) recorded from several sites of lower limbs. The purpose was to obtain normative variability values to detect significant changes in the individual patient in follow up studies. Maximal CMAPs to HVES of lumbo-sacral roots were obtained from 10 proximal and distal muscle districts of lower limbs; MEPs to TMS using the double cone coil were recorded from the same sites. The procedure was repeated twice, 1–2 days apart, in 30 subjects, including healthy volunteers and clinically stable multiple sclerosis patients. The use of stable recording and stimulation sites with maximal root-CMAPs and adequately stabilized MEPs allowed a significant reduction of ITV for all latency and area parameters. Mean RIV values (5th–95th percentile) for Central Motor Conduction Time and Area Ratio (MEP/CMAP) did not exceeded −14.8 and +16.0 ms and −26.0 and +33.7 mV ms, respectively. The combined monitoring of latency and areas indexes allows assessment of both conduction slowing and conduction failure, i.e the variable association of axonal damage and conduction block, which directly correlates with motor impairment. [ABSTRACT FROM AUTHOR]