Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice provides an overview of electromyography (EMG) and electrodiagnosis. It discusses the key concepts of nerve conduction studies, electromyography, intraoperative monitoring, and somatosensory and motor evoked potential. Jun Kimura’s fifth edition of Electrodiagnosis in Diseases of Nerve and Muscle offers a comprehensive text on electromyography that will be useful to both beginning practitioners and experts alike. The fifth edition is expected to be important as a world-class reference in the subspecialty of neurophysiology as it is part of Kimura's legacy. The updates within the new edition include further information on the increasing complementary utilities of neuromuscular ultrasound.

This chapter details the principles of nerve conduction studies (NCS). It cites that the NCS became a simple and reliable test of peripheral nerve function to identify the lesion and the site of maximal involvement. The assessment of conduction characteristics depends on the analysis of compound evoked potentials recorded from the muscle in the study of motor fibers and from the nerve itself in the case of sensory fibers. The chapter then provides an overview of the electrical stimulation of the nerve and the recording of muscle and nerve potentials. It also discusses the differences between motor nerve conduction and sensory nerve conduction.

Objective To study mild to moderate carpal tunnel syndrome (CTS), compare median nerve entrapment sites detected by electrophysiological inching studies with ultrasonographic abnormalities of cross-sectional area (CSA), and correlate focal points of conduction delays detected by sensory and motor inching recorded from the third digit and second lumbrical muscle. Design Analytic cross-sectional study. Setting Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Participants Hands from 10 participants without CTS (n=15) and hands with mild to moderate CTS from 29 participants (n=40) were selected by convenience sampling (N=55). Interventions Not applicable. Main Outcome Measures Correlation of electrophysiological entrapment site localization by inching study with anatomic entrapment site detected by ultrasound (US). Results In all 40 hands tested, a sharply localized latency was found to increase across a 1-cm segment, most commonly 2-3 cm distal to the distal wrist crease for both sensory and motor studies, showing a good match between the 2 with Pearson correlation coefficient value (r=0.72). US revealed a narrowing CSA of the median nerve at 1-2 cm distal to the distal wrist crease. Conclusions This study showed a high correlation for focal point conduction delay detected by sensory and motor nerve conduction study. Recording from the second lumbricalis facilitated motor inching along the straight course of the nerve instead of the arcuate recurrent branch innervating the abductor pollicis brevis, the muscle traditionally used. US examination also revealed a localized narrowing of the median nerve CSA at 1-2 cm distal to the distal wrist crease, a possible site for anatomic entrapment. The most enlarged CSA was seen at the distal wrist crease, a level corresponding to the inlet of the carpal tunnel.

Introduction. The electrodiagnosis of CTS continues to evolve with renewed interest centering on the clinical use of mid-palmar stimulation and inching study. We reanalyzed our data (Neurology 1979;29: 581 [abstract]) on distal conduction abnormalities in DPN and CTS to discuss pros and cons of currently available nerve conduction techniques. Methods. We stimulated the median nerve at the wrist and mid palm to record muscle responses from the abductor pollicis brevis and sensory potentials from the index finger in 40 nerves from 22 DPN patients, 38 nerves from 24 CTS patients and 50 nerves from 25 normal controls (NL). Of these DPN patients, 24 median nerves were examined by a sensory inching study with 1 cm incremental stimulation. Results. The wrist-to-palm segment showed a significant (P< 0.001) increase in motor and sensory conduction time (mean ± SD ms) in DPN (2.25 ± 0.67 and 1.80 ± 0.38) and CTS (2.21 ± 1.34 and 1.59 ± 0.50) compared with NL (1.15 ± 0.21 and 1.12 ± 0.21). In contrast, the terminal segment from the palm had significantly (P < 0.001) prolonged latencies in DPN (2.58 ± 0.58 and 1.70 ± 0.42) compared to either CTS (2.01 ± 0.36 and 1.35 ± 0.27) or NL (1.86 ± 0.36 and 1.34 ± 0.31). Inching studies, known to identify an abnormal latency shift localized to 1 cm segment in majority of CTS hands, revealed such focal slowing in only 3 of 24 (12%) DPN hands. Unlike DPN, typically resulting in a diffuse, distal slowing of both motor and sensory conduction, CTS characteristically shows a sharply localized lesion near the distal edge of the transverse carpal ligament. Other techniques useful in identifying a subtle conduction abnormality may include single fiber recording, which helps document a delay affecting only a limited number of motor axons. Conclusion. Mid-palmar stimulation and inching method can distinguish diffuse slowing in DPN from a localized change in CTS along the distal segment of the median nerve.

Polyneuropathy consists of the triad of sensory changes in a glove and stocking distribution, distal weakness, and hyporeflexia. Certain types of neuropathy may show widespread sensory symptoms, and others may begin with more prominent proximal weakness. Positive sensory symptoms result from ectopic impulse generation and auto excitation of myelinated afferent fibers. In general, but not always, normal muscle stretch reflexes speak against peripheral neuropathy. Acute pandysautonomic neuropathy characteristically shows severe postganglionic sympathetic and parasympathetic dysfunction, with relative or complete sparing of motor and sensory function. Milder autonomic dysfunction also accompanies most peripheral neuropathies, but manifests clinically detectable symptoms only in a few conditions, such as diabetes, amyloidosis, Guillain- Barre syndrome, porphyria, and familial dysautonomia. A detailed history often reveals general medical conditions such as diabetes, alcoholism, renal disease, malignancies, sarcoidosis, polyarteritis nodosa, amyloidosis and infectious processes such as diphtheria and leprosy. Inflammatory neuropathies include the Guillain-Barre syndrome and chronic inflammatory demyelinative neuropathy. Metabolic neuropathies result from nutritional deficiencies or the toxic effects of drugs or chemicals. The family history is essential in establishing the type of inherited conditions associated with polyneuropathy. Sometimes a patient's own account may not provide enough information, necessitating independent examination of family members. For some patients with an unequivocal diagnosis of polyneuropathy, extensive studies may fail to uncover the exact etiology. Hereditary and immune mediated polyneuropathy account for most such cases. Anatomic diagnosis depends on clinical and electrodiagnostic evaluation, but few specific patterns of peripheral nerve involvement characterize a given disorder. Nerve conduction and electromyographic studies delineate the extent and distribution of the lesions and differentiate two major pathologic changes in the nerve; axonal degeneration and demyelination. An index based on multiple electrophysiologic measures against standard norms may provide a better overall estimation as reported in the assessment of diabetic polyneuropathy. Electrodiagnosis, as discussed in detail during our workshop, helps delineate the locations and patterns of abnormalities, but these studies alone rarely distinguish clinical types of neuropathies or establish the exact etiology in a given case. Arriving at a specific diagnosis and establishing a course of therapy depend heavily on clinical, electrophysiologic and histologic assessments.

Objective: We report a case of sustained atypical myokymia associated with short bursts of neuromyotonic discharges involving the abductor pollicis brevis (APB) muscle and describe a useful way of detecting a focal slowing involving a small number of median nerve motor fibers with a concentric needle using the filter setting for single fiber electromyography (EMG). Methods and Results: A 62-year-old woman developed right thumb twitches at regular interval of 1.7-3.3 s (0.6-0.3 Hz), which continued for more than four months. Muscle twitches remained the same during altered hand position, psychological stress, or sleep. A concentric needle inserted in the active zone of the APB muscle revealed myokymic bursts with a characteristic of neuromyotonic discharges. Inching study, stimulating at 5 mm increment along the median nerve and recording with a concentric needle using a filter setting for single fiber EMG, revealed a focal slowing of the motor fibers at a point 5-10 mm distal from the distal crease of the wrist, an entrapment site occasionally seen in the carpal tunnel syndrome. One injection of botulinum toxin type A eliminated the myokymia, which then recurred two and a half years later, showing less prominent muscle twitches. Conclusions: Sustained atypical myokymia seen in our case represented bursts of neuromyotonic discharges originated from a focal demyelinating lesion involving a few median nerve motor fibers. (C) 2020 Published by Elsevier B.V. on behalf of International Federation of Clinical Neurophysiology.

To study if spinal motor evoked potentials (SpMEPs), muscle responses after electrical stimulation of the spinal cord, can monitor the corticospinal tract. Study 1 comprised 10 consecutive cervical or thoracic myelopathic patients. We recorded three types of muscle responses intraoperatively: (1) transcranial motor evoked potentials (TcMEPs), (2) SpMEPs and (3) SpMEPs + TcMEPs from the abductor hallucis (AH) using train stimulation. Study 2 dealt with 5 patients, who underwent paired train stimulation to the spinal cord with intertrain interval of 50–60 ms for recording AH SpMEPs. We will also describe two illustrative cases to demonstrate the clinical value of AH SpMEPs for monitoring the motor pathway. In Study 1, SpMEPs and SpMEPs + TcMEPs recorded from AH measured nearly the same, suggesting the collision of the cranially evoked volleys with the antidromic signals induced by spinal cord stimulation via the corticospinal tracts. In Study 2, the first and second train stimuli elicited almost identical SpMEPs, indicating a quick return of transmission after 50–60 ms considered characteristic of the corticospinal tract rather than the dorsal column, which would have recovered much more slowly. Of the two patients presented, one had no post-operative neurological deteriorations as anticipated by stable SpMEPs, despite otherwise insufficient IONM, and the other developed post-operative motor deficits as predicted by simultaneous reduction of TcMEPs and SpMEPs in the face of normal SEPs. Electrical stimulation of the spinal cord primarily activates the corticospinal tract to mediate SpMEPs.

The demand for intraoperative monitoring (IOM) of lumbar spine surgeries has escalated to accommodate more challenging surgical approaches to prevent perioperative neurologic deficits. Identifying impending injury of individual lumbar roots can be done by assessing free-running EMG and by monitoring the integrity of sensory and motor fibers within the roots by eliciting somatosensory (SEP), and motor evoked potentials. However, the common nerves for eliciting lower limb SEP do not monitor the entire lumbar plexus, excluding fibers from L1 to L4 roots. We aimed to technically optimize the methodology for saphenous nerve SEP (Sap-SEP) proposed for monitoring upper lumbar roots in the operating room. In the first group, the saphenous nerve was consecutively stimulated in two different locations: proximal in the thigh and distal close to the tibia. In the second group, three different recording derivations (10–20 International system) to distal saphenous stimulation were tested. Distal stimulation yielded a higher Sap-SEP amplitude (mean ± SD) than proximal: 1.36 ± 0.9 µV versus 0.62 ± 0.6 µV, (p < 0.0001). Distal stimulation evoked either higher (73%) or similar (12%) Sap-SEP amplitude compared to proximal in most of the nerves. The recording derivation CPz–cCP showed the highest amplitude in 65% of the nerves, followed by CPz–Fz (24%). Distal stimulation for Sap-SEP has advantages over proximal stimulation, including simplicity, lack of movement and higher amplitude responses. The use of two derivations (CPz–cCP, CPz–Fz) optimizes Sap-SEP recording.

OBJECTIVE:To summarize the neurophysiological properties of acute flaccid myelitis (AFM) and evaluate limb-based motor outcomes. METHODS:Nerve conduction studies (NCS) in 49 patients (21 females, 28 males; median age = 52 m) with AFM (median = 7 d after onset; range 1-122 d) were reviewed. Neurophysiological findings, together with treatment and prognosis, and neurophysiology-neuroimaging correlations were analyzed. RESULTS:The findings indicated that 64% of paralytic limbs during the acute stage (≤14 d after onset) showed diminished or absent compound muscle action potentials (CMAPs), 79% showed normal motor nerve conduction velocities, 55% showed decreased persistence or absent F-waves, and 95% showed normal sensory nerve conduction velocities. The rate of CMAP abnormalities increased from 41% on days 1-2 to 83% on days 13-14. The reduction in CMAP amplitude was correlated with weaker muscle strength at both the peak neurological deficit and the last follow-up. The baseline limb-based muscle strength at nadir and anterior horn-localized magnetic resonance imaging lesions at recovery stage (>14 d) were strong predictors of outcome at the last follow-up. CONCLUSIONS:AFM typically shows neurophysiological features of neuronopathy. SIGNIFICANCE:NCS is probably useful in the diagnosis and evaluation of AFM.

OBJECTIVE:To establish a clinician-led guideline for the diagnosis and treatment of Hirayama disease (HD) using a modified Delphi technique. METHODS:Based on a combination of a systematic review and opinion of ten experts, a protocol for the consensus of the diagnosis, treatment and follow-up assessment of HD was established. A modified 3-round Delphi survey was then performed by more than 40 panelists from various countries of the world. Both levels of evidence and levels of agreement were derived in all statements of finial guideline. RESULTS:A total of 47 experts from 6 countries were enrolled in the expert panel in this study. Highly consistent results were achieved during the three Delphi rounds. An expert-led guideline finally constructed includes 24 statements related to diagnosis, treatment and follow-up assessment of HD. CONCLUSIONS:The modified Delphi technique used in this study resulted in an expert-led guideline concerning several clinical aspects of HD. SIGNIFICANCE:This clinician-led guideline may provide a helpful direction for clinical practice with regard to the diagnosis and treatment of HD.

OBJECTIVE:To establish age-related characteristics and normative values of F waves in healthy Chinese infants. METHODS:We studied median, ulnar and tibial nerves on one side distally in 229 healthy Chinese infants (108 males) ranging from 1 to 12 months old. RESULTS:Minimal F-wave latencies (Fmin) showed a strong negative correlation to the age for median, ulnar and tibial nerves (P < 0.01) but no correlation to the height. Statistical analyses revealed a significant (P < 0.01) decrease of Fmin during the second month of life and no change (P > 0.05) thereafter. Dividing the infants into 1 month old (Group 1) and 2-12 months old (Group 2), normal values (Mean ± SD ms) of Fmin for tibial, median and ulnar nerves consisted of 23.38 ± 1.68, 17.19 ± 0.95 and 16.47 ± 1.06 for Group 1 and 21.42 ± 1.25, 14.50 ± 1.15 and 14.52 ± 0.90 for Group 2. CONCLUSION:F-wave latencies shorten in the 2nd month of life and change little thereafter when age-related maturation counters the concomitant growth of the nerve length. SIGNIFICANCE:F waves can assess infantile neuropathies as a reliable measure, complementing the technically difficult conventional nerve conduction study in short limbs.

AIM:Absence of the F-wave may represent the inability of spinal motor neurons to be excited after periods of inactivity. Repetitive stimulation in an otherwise immobile patient acts as a voluntary movement therefore allowing for the production of an F-wave in a patient with previously demonstrated absent F-waves. Through this case report, we attempt to highlight that the absence of the F-wave may result from inexcitability of spinal motor neurons after reduced mobilization.CASE:We present the case of a 48-year-old woman who had been hospitalized in an ICU setting for almost one month due to a subarachnoid hemorrhage, pancreatitis, and respiratory failure. An electromyogram and nerve conduction study (NCS) was performed for weakness in all four extremities. On routine NCS, her F-waves were absent, but after repetitive stimulation was performed, her F-waves appeared.DISCUSSION:This may be further evidence that the absence of the F-wave may result from inexcitability of spinal motor neurons after immobilization or reduced mobility rather than true pathology of the peripheral nerve. The ability to recover F-waves after an initial absence could assist in differentiating between inexcitability of the anterior horn cell and proximal nerve conduction block. This case presentation is an attempt to show that repetitive nerve stimulation may prove to be a useful technique to restore F-waves in patients who are unable to voluntarily contract their muscles, which may help exclude certain pathologic processes.

To establish age related characteristics and normative values of F wave in healthy Chinese infants. We studied median, ulnar and tibial nerves on one side in 229 healthy Chinese infants (108 males) ranging from 1 to 12 months old in age. EDX studies consisted of stimulating each nerve at the wrist or ankle 16 times and recording F-wave amplitude, persistence, duration and minimal and maximal latencies in addition to M-response amplitude and latency. Minimal F-wave latencies (Fmin) showed a strong negative correlation to the age for median (r = −0.21, P < 0.01), ulnar (r = −0.22, P < 0.001) and tibial nerves (r = −0.30, P < 0.001) but not correlation to the height for these nerves. The normal range of Fmin (mean ± SD ms) for the tibial nerve, which serves best for clinical evaluation, comprised 23.26 ± 1.71, 20.89 ± 1.91, 21.36 ± 1.84, 20.28 ± 2.05, 20.41 ± 1.89, 21.21 ± 1.77, 20.43 ± 1.69, 21.42 ± 2.81, 20.77 ± 1.24, 20.40 ± 1.24, 20.72 ± 1.24, and 20.32 ± 1.35 for age 1–12 months old. Statistical analyses revealed a significant (P < 0.01) decrease of Fmin during the second month of life and no change (P > 0.5) thereafter. We suggest the use of F waves to assess infants with neuropathic disorders as a reliable measure to complement the conventional nerve conduction study, which poses a major technical limitation for the short limbs.

Late responses include F waves, A waves, H reflex, and the blink reflex. These responses help enhance routine nerve conduction studies. Despite the use of F waves in multiple clinical applications, their studies can technically challenge even the most experienced electromyographers. They vary in latency, amplitude, and configuration, whereas A waves show no change in latency or morphology. Electrical stimulation of the supraorbital branch of the trigeminal nerve on one side results in a reflexive activation of the facial nucleus causing contraction of the orbicularis oculi muscle, short latency R1 ipsilaterally, and long latency R2 bilaterally. F waves can help determine the presence of a polyneuropathy. A waves can reflect axonal damage. H reflexes provide nerve conduction measurements along the entire length of the nerve, demonstrating abnormalities in neuropathies and radiculopathies. Abnormalities in the blink reflex can suggest the presence of an acoustic neuroma or a demyelinating polyneuropathy, which can affect the cranial nerves. This reflex, which also needs appropriate technical expertise, helps to assess cranial nerves V and VII along with their connections in the pons and medulla. The blink reflex, the electrical version of the corneal reflex, represents a polysynaptic reflex.

The presence of sensory nerve conduction block is not routinely assessed in the evaluation of patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Whether this can be useful is not well known. We respectively analyze the serial sensory conduction studies of 20 patients with the diagnosis of typical CIDP. Sensory nerve action potential (SNAP) amplitudes and sensory conduction velocities were recorded in the median, ulnar, tibial, peroneal and sural nerves. Follow-up studies were compared with the baseline to evaluate the variation of SNAP amplitudes in serial recordings. Four patients were excluded because of clinical aggravation, and the data of sixteen patients were analyzed, including serial sensory conduction studies in 136 nerves. The SNAPs in 82 nerves were absent at baseline, of which the SNAPs in 24 nerves reappeared during follow-up studies, with a mean amplitude of 3.23 ± 3.57 μV. In the other 54 nerves, 36/54 (66.7%) SNAP amplitudes increased (median increased by 45%) compared to the baseline, and the improvement rates in 15 nerves were greater than 50%. The mean increase in median nerve was the highest (r = 56.64%), followed by tibial nerve (r = 46%), sural nerve (r = 38.75%), ulnar nerve (r = 28.4%), and peroneal nerve (r = 15.75%). Notably, 20/29 (68%) initially normal sensory nerves showed significant increase in SNAP amplitude (median increased by 37.5%), and the improvement rates in 6 nerves were greater than 50%. We propose that conduction block may also exist in sensory nerves, segmental sensory conduction and follow-up studies may be of great value in evaluating patients with CIDP.

Waveform analysis plays an important role in the assessment of nerve and muscle action potentials. A sequence of potential changes arises as two sufficiently close wave fronts, leading and trailing dipoles, travel in the volume conductor from left to right. This results in a positive-negative-positive triphasic wave as depolarization and repolarization approach, reach, and finally pass beyond the point of the recording electrode. Physiologic temporal dispersion can reduce the area of a short-duration sensory potential by phase cancellation. Pathologic temporal dispersion, which can reduce the size of muscle action potential, may conversely increase the size of a sensory response by countering the physiologic phase cancellation. The near-field potential relates to the propagating signal recorded when the impulse passes under the pickup electrodes, whereas the far-field potential implies either a distant nonpropagating signal or a stationary peak generated by a propagating signal when it crosses a volume conductor junction located far from the recording site. The second type of far-field signal, or junctional potential, helps detect a voltage source generated at a distance before the signal reaches the pickup electrodes. A consensus has emerged that the volume entered becomes initially positive compared with the volume departed when the generator approaches the boundary of a volume conductor followed by a negative rebound.

This document is an update and extension of ICCN Standards published in 1999. It is the consensus of experts on the current status of EMG and Neurography methods. A panel of authors from different countries with different approach to routines in neurophysiological methods was chosen based on their particular interest and previous publications. Each member of the panel submitted a section on their particular area of interest and these submissions were circulated among the panel members for edits and comments. This process continued until a consensus was reached. The document covers EMG topics such as conventional EMG, Macro EMG, applications of surface EMG and electrical impedance myography. Single Fiber EMG is not included, since it is the topic in a separate IFCN document. A neurography section covers topics such as motor and sensory neurography, F wave recordings, H-reflex, short segment recordings, CMAP scan and motor unit number methods. Other sections cover repetitive nerve stimulation and Pediatric electrodiagnostic testing. Each method includes a description of methodologies, pitfalls, and the use of reference values. Clinical applications accompany some of these sections.

Multifocal motor neuropathy (MMN) almost purely involves motor nerve. About 20% MMN patients develop minor sensory symptoms in the course of disease. We reported a 62-year-old male who developed a slowly progressive asymmetrical limb weakness for five years. Motor nerve conduction studies showed definite CB in left median and ulnar nerves, and probable CB in right tibial nerve. Although the patient complained of no sensory symptom, sensory never conduction studies showed absent sensory nerve action potential (SNAP) for bilateral medial plantar and fibular nerves, left sural nerve and reduced amplitude for left median, ulnar and radial nerves. Conduction velocities were otherwise normal. One month after receiving intravenous immunoglobulin (IVIg), his weakness alleviated apparently. A substantial increase in motor amplitude recorded with stimulation at the PF indicated a partial reversal of CB. The SNAP amplitude of left median, ulnar and radial nerves increased more than 50% and the return of bilateral fibular nerve potentials provided evidence of reversible conduction failure in sensory nerves. We reviewed related literature for this performance. Three previously published studies reported such a decrease of SNAP amplitude in MMN patients. Such features suggest a more prominent axonal damage more than demyelination. The hyperpolarization of axolemma, resulting from axonal Na+/K+ pump inhibition at the lesion site and overactivity at the adjacent site may constitutes the prominent mechanism of CB. Amplitude reduction of SNAP combined with motor CB, which recovered rapidly after IVIg, may suggest axonal damage rather than demyelination.

With the short length of the facial nerve, its F waves tend to appear before the M waves finish, limiting its clinical application. To circumvent this difficulty, we have sought to investigate the methodology on how to better elicit the facial nerve F-wave and to establish its reference values, which provides an electrophysiological basis for facial nerve assessment in clinical practice. We studied 41 healthy volunteers (19 men) aged 19 to 68 years old (mean 44.3 years). Head circumference ranged from 51.0 to 58.5 cm (mean circumference, 55.0 cm). F waves were elicited by 1 Hz supramaximal stimuli of 0.2 ms duration, using AgCl surface electrodes placed on the marginal mandibular branch of the facial nerve. The cathode was positioned as distally as possible, with the anode placed 2 cm more proximally along the presumed course of the nerve. The recording electrode was put on the depressor anguli oris muscle, with a reference electrode located on the tip of the chin. The distance between stimulation and recording sites was usually kept about 2 cm. We used a gain of 200 μv/div, sweep speed at 5 ms/div and the filter width of 30 Hz-10 kHz to evaluate minimum, maximum, and mean F-wave latency, F-wave chronodispersion, F-wave conduction time (FWCT), peripheral conduction time (PCT), F ratio (FWCT/distal motor latency) and F-wave persistence. We successfully obtained bilaterally reliable F waves, which were clearly distinguished from the M waves. There was no significant difference in the values of F waves between men and women, or between the two sides. No correlations with age, sex, or head circumference could be detected. The measured values included minimum (8.97 ± 0.53 ms; range, 7.81–10.2 ms), maximum (9.74 ± 0.54 ms; range, 8.39–10.4 ms), and mean F-wave latency (9.39 ± 0.51 ms; range, 8.14–10.5 ms), broadly scattered F-wave chronodispersion (0.80 ± 0.31 ms; range, 0–1.77 ms), F-wave conduction time (2.92 ± 0.29 ms; range, 2.17–3.53 ms), peripheral conduction time (5.47 ± 0.31 ms; range, 4.78–6.19 ms), F ratio (1.17 ± 0.24; range, 0.72–1.90) and F-wave persistence (100% ± 0%; range, 90–100%). We hereby established a method to elicit facial nerve F-wave by stimulating the marginal mandibular branch, and recording from the depressor anguli oris muscle and defined a range of reference values in a Chinese healthy population. These findings provide an objective basis for an evaluation of the entire length of the facial nerve.

The motor neuronal damage is selective in the early stage of amytrophic lateral sclerosis (ALS), and the large motor neurons with rapid conduction may be the earliest involved. The purpose of this study is based on the analysis of the correlation between the changes of F wave minimum latencies, distal motor latencies (DML) and the compound muscle action potentials (CMAP) and negative area of CMAP to seek for the evidence supporting preferential vulnerability of fast motor neuron in early stage of ALS. This study enrolled the definite and probable diagnosis ALS (according to revised EI criteria) patients in our outpatient clinic from January 2016 to October 2017. The inclusion criteria of early ALS patients: the strength of upper limbs higher than 3/5 MRC levels and revised ALS-FRS score greater than 25 points. In addition, the matched healthy people were selected as the control group. All participants were evaluated by physical examination, nerve conduction studies, and standard needle EMG and we focused on the values including DML, CMAP (from the baseline to negative wave peaks), negative peak area and F wave of minimum latencies in the median nerve. Forty-five patients (27 male) of ALS group, mean 55.8 ± 11.9 years, height 165.8 ± 6.7 cm,duration of disease 12.3 ± 6.3 months, revised ALS-FRS score 31.5 ± 4.1. The site of symptom onset from upper limb was 27 (60%), and from bulbar was 18 (40%). In the normal control group, there were 46 (27 male) subjects, mean 56.3 ± 12.0 years, height 164.6 ± 7.4 cm. Age, gender and height matched with ALS group. DML in the median showed no significant difference (P = 0.138) between control and ALS group, meanwhile the median nerve conduction velocity showed in normal range. But the minimal latencies of F wave revealed more longer (P < 0.001) in ALS group than control group. The abnormal incidence of the median nerve F-wave minimal latency was 34.8%, while the prolonged latencies did not exceed 120% of the upper limit of normal. CMAP decreased significantly when compared with control group (P < 0.001), so did the negative area of CMAP (P < 0.001), and the abnormal rate of CMAP was 37.8%. The median nerve CMAP and negative wave area were negatively correlated with DML (R = −0.593, P ± 0.001; R = −0.530, P = 0.001), and did the same pattern to the F wave minimum latency (R = −0.635, P = 0.001; R = 0.634, P = 0.001). Based on the evidence of negative correlation between mildly prolonged the minimal latency of the F wave and decreased CMAP or negative wave area, the fast motor neurons show preferentially vulnerable in the early stage of ALS.