The Compound Muscle Action Potential in LEMS.

Case studies of patients with cervical spondylotic amyotrophy used compound muscle action potentials (CMAPs) of deltoid and biceps brachii muscles and central motor conduction time (CMCT). To discuss surgical outcome for proximal-type cervical spondylotic amyotrophy in the context of results obtained with CMAPs and CMCT. There have been no reports that correlate surgical outcome with CMAPs of deltoid and biceps brachii muscles or with CMCT. A retrospective study was performed for 24 patients with proximal-type cervical spondylotic amyotrophy who underwent surgical treatment of the cervical spine. Erb-point-stimulated CMAPs were recorded in the deltoid and biceps. The percent amplitude of CMAPs was calculated in comparison with the opposite side. Motor-evoked potentials were recorded from bilateral abductor digiti minimi. CMAPs and F waves were recorded after supramaximal electric stimulation of ulnar nerves. CMCT was calculated as follows: motor-evoked potentials latency - (CMAPs' latency + F latency - 1)/2 (ms). Muscle strength was evaluated using manual muscle testing. Improvements in strength were classified as excellent, good, or fair. The improvement was graded as excellent in 12 cases, good in 2 cases, and fair in 10 cases. The average percentage for CMAPs' amplitude on the affected side compared with the normal side in deltoid and biceps brachii muscles was significantly different between the excellent and fair patient groups. The CMCT on the affected side was not significantly different between excellent and fair patient groups. The average percentage range of deltoid and biceps brachii muscle CMAPs' amplitude determined at the onset of illness correlated significantly with postoperative recovery. Surgical intervention of the cervical spine should be performed in patients in whom the average percentage of CMAPs' amplitude in deltoid and biceps brachii muscles ranges from 30% to 50%.

Supramaximal responses can be elicited in hand muscles by magnetic stimulation of the cervical motor roots

G.P.293: Peripheral nerve conduction abnormalities in amyotrophic lateral sclerosis

Case studies of patients with cervical spondylotic amyotrophy (CSA) used compound muscle action potentials (CMAPs) of deltoid and biceps brachii muscles. To discuss pathology and prognosis from the magnetic resonance imaging (MRI) and CMAPs of deltoid and biceps brachii muscles. CSA is a rare type of cervical spondylotic disorder. Selective lesions in ventral nerve roots (VNR) or anterior horns (AH) have been proposed to explain the pathology of CSA, but these are not well understood. Conservative therapy was performed in 21 patients with the proximal-type CSA. Patients were classified into two groups: 13 with incomplete recovery of deltoid and biceps brachii muscle strength (Group 1) and 8 with complete recovery (Group 2). All underwent MRI. Erb-point-stimulated CMAPs were recorded in the deltoid and biceps. Measurements of CMAPs included negative-peak amplitude from the baseline to peak. The percentage amplitude of CMAPs was calculated in contrast to the opposite side. Sagittal T2-weighted MRI showed spinal cord compression in all patients from Group 1 and in four patients from Group 2. Deltoid muscle CMAPs: Three patients from Group 1 and all eight patients from Group 2 had a CMAPs' amplitude on the normal side that was greater than 10 mV. Biceps brachii muscle CMAPs: four patients from Group 1 and four patients from Group 2 had a CMAPs' amplitude on the normal side that was greater than 10 mV. Patients with a CMAPs amplitude on the normal side that exceeded 10 mV had no impingement of the AH. A CMAPs' amplitude that exceeded 10 mV on the normal side and a CMAPs' amplitude of more than 50% on the affected side compared with the normal side indicated slight involvement of VNR. These patients were able to fully recover function.

Background: The aim of this study was to demonstrate an increase in muscle action potentials and an enhancement of the efficacy of botulinum toxin (BoNT) after mechanical leg vibration. Methods: A 53-year-old healthy male volunteer underwent vibration ergometry training (VET) every morning and every evening for 10 min for 14 days. Compound muscle action potential (CMAP) of the right (R) and left (L) extensor digitorum brevis (EDB) muscle was analyzed by supramaximal peroneal nerve stimulation before and after VET 12 times during the 14 days. Thereafter, VET was stopped and 20 U incobotulinumtoxin (incoBoNT/A) were injected into the right EDB. During the following 10 days, CMAP of both EDBs was tested 12 times. Results: Under VET, the CMAP of both EDBs significantly increased (L: p < 0.01; R: p < 0.01). During the first 14 days, CMAP of the left EDB before VET was significantly (<0.008) lower than 20 min later after VET. This was not the case for the better trained right EDB. After day 14, CMAP of the untreated left EDB further increased for 6 days and then decreased again. In the right EDB, BoNT-treated EDB CMAP rapidly and highly significantly (p < 0.0001) decreased during the first 48 h by about 90%, from a level of about 14 mV down to a plateau of around 1.5 mV. Conclusion: Local mechanical leg vibration has a short- and long-term training effect. Compared to other studies analyzing the reduction in EDB CMAPs after BoNT injections, the reduction of EDB CMAPs in the present study observed after combined application of BoNT and VET was much faster and more pronounced.

P15.20 The formation features of compound muscle action potential from anterior forearm muscles at brachial plexus stimulation

Objective To investigate the F-wave and nerve conduction in patients with amyotrophic lateral sclerosis (ALS) and explore the correlation between these parameters and muscle strength, disease duration and onset site.Methods The data of outpatients and inpatients diagnosed with ALS were collected in Peking Union Medical College Hospital from January 1997 to May 2008.Standard sensory and motor nerve conduction study of the median nerve, ulnar nerve and tibial nerve was performed in 205 patients with ALS.F-wave velocity and frequency was measured in median nerve.Parameters for analyses included sensory conduction velocity and amplitude, distal motor latency (DML), and compound muscle action potential (CMAP) amplitude.Correlation between muscle strength and DML, CMAP amplitude or F-wave frequency were also explored.Results Delayed DML of the median nerve, ulnar nerve and tibial nerve were found in 24.9% (48/193), 15.3% (25/163), 21.2% (7/33) of patients respectively.Decreased CMAP amplitudes were found in 57.0% (110/193), 49.7% (81/163), 39.4% (13/33) of patients respectively.Decreased F-wave frequency of the median nerve was found in 68.9% (122/177) of patients.The abnormality of DML,CMAP amplitude and F-wave frequency of median nerve were increased in weaker muscles.Decreased median nerve CMAP amplitude (81.5% (53/65)) and F-wave abnormality (decreased persistence 70.9%(44/62), absent responses 45.1% (28/62)) in spinal onset groups were significantly higher than those in bulbar onset groups (CMAP 32.4% (11/34); F-wave: decreased persistence 38.2% (13/34), absent responses 14.7% (5/34); x2 = 23.629, 9.753, 9.029,all P <0.01).Compared with the bulbar onset group,the abnormality of DML in spinal onset group was higher, but not reach statistical significance.Logistic regression revealed a strong direct association between decreased CMAP amplitudes and upperextremity muscles strength, disease duration and onset symptom.Abnormality of F-wave frequency was associated with upper-extremity muscles strength and onset symptom.Conclusions Delayed DML and decreased amplitude of CMAP are found in ALS patients.CMAP amplitude is a sensitive parameter related to the severity of ALS.F-wave velocity is relatively normal while F-wave frequency of the median nerve is correlated with muscle strength.Decreasing CMAP amplitude and F-wave frequency are correlated strongly with muscle weakening,disease duration and symptom onset over limbs. Key words: Amyotrophic lateral sclerosis; Nerve conduction

Objective To study the operation method of the post-exercise facilitation (PEF) in Lambert-Eaton myasthenic syndrome (LEMS), and to seek for the meaning of PEF in clinical work. Methods Eleven patients with LEMS were included to accept the PEF and the repetitive nerve stimulation (RNS) test. When performing the PEF test, compound muscle action potentials (CMAPs) of abductor digitiminimi were recorded after a specified time of exercise. The patients would get rest for 1 minute before the next test. The same exercises were repeated for several times. The exercise time started from 0 second, and 2 seconds was added each time until the CMAP did not increase. The PEF or RNS test was followed by a continuous stimuli at 0.5 Hz and the CMAPs were recorded to study the recovery process. Results The CMAPs of abductor digitiminimi increased significantly after PEF. The median time for CMAPs to achieve its maximum was 12(10, 14) seconds. The recovery processes of PEF and RNS showed that the CMAP would return to normal after (50.4±16.0) seconds. Conclusions Patients with suspected LEMS might get a 10-12 seconds of PEF test instead of RNS for it is fast and painless. If the potential of CMAPs increased ≥60%, the result would be positive. If the potential of CMAPs increased ≤24%, the result would be negative. A suspicious increments of CMAPs (increasing by 24%-60%) should warrant a further RNS test. And the interval between the two tests should be longer than (50.4±16.0) seconds. Key words: Lambert-Eaton myasthenic syndrome; Post-exercise facilitation; Electric stimulation; Electrophysiology

Using compound muscle action potentials after train spinal stimulation, intraoperative motor functional monitoring was performed during thoracic and thoracolumbar spinal surgery. This study was designed to clarify the clinical usefulness of train spinal stimulation and to determine the critical point of compound muscle action potential change at which neurologic injury during surgery occurs. In 1995 the authors reported that train spinal stimulation allows for the recording of compound muscle action potentials, even in animals and humans under general anesthesia. The facilitative effect of train stimulation overcomes the suppressive effects of anesthetics and allows potentials to pass through synapses, thereby enabling a reliable recording of lower extremity compound muscle action potential. Multisegmental recording of compound muscle action potentials after train spinal stimulation was conducted on 34 patients Undergoing surgical treatment for thoracic or thoracolumbar lesions. During surgery, train stimuli (5 pulse, Interstimular Interval: 1 ms) were administered using an epidural electrode introduced transcutaneously. Compound muscle action potentials were recorded from a total of 128 muscles. Anesthesia was maintained using fentanyl and propofol or nitrous oxide with or without isoflurane. Muscle relaxation was attained mainly by controlled infusion of vecuronium bromide. The percent occurrence of recordable compound muscle action potentials was determined, and the potential changes were correlated with changes in muscle strength. Compound muscle action potentials could be recorded from at least one muscle in 94% of the patients, even in most patients with severe motor dysfunction. The compound muscle action potential changes before and after surgical maneuver were divided into four grades. All compound muscle action potential changes in deteriorated muscles belonged to Grade 2 (a 10% latency delay) or Grade 3 (disappearance). The success rate in obtaining muscle potentials was greatly enhanced when all of the following methods were used: train spinal stimulation, anesthetic with weak suppressive effect, multiple muscle recording, and percutaneous introduction of epidural electrode. The critical point of compound muscle action potential change should be defined as a 10% latency delay or disappearance. Multisegmental muscle potential after train spinal stimulation is the most appropriate method for thoracic and thoracolumbar spinal surgery.

ABSTRACTBackgroundThis study aimed to evaluate changes in compound muscle action potential (CMAP) amplitude in adults with spinal muscular atrophy (SMA) undergoing nusinersen treatment and its association with motor function improvements.MethodsThis multicenter study assessed median, ulnar, and peroneal CMAP over a follow‐up of up to 4.5 years using linear mixed models. Motor function was measured using the Revised Upper Limb Module (RULM) and the Hammersmith Functional Motor Scale Expanded (HFMSE). Correlations between CMAP and motor function scores were analyzed.ResultsSeventy‐eight patients (27 ambulatory, 51 non‐ambulatory) were included. Baseline ulnar CMAP ≥ 2.0 mV distinguished SMA type 3 from type 2 with 91.3% sensitivity and 88.9% specificity (AUC 0.96, 95% CI 0.92–1.0), while baseline median nerve CMAP ≥ 6.5 mV showed 91.7% sensitivity and 77.3% specificity (AUC 0.84, 95% CI 0.72–0.96). No significant changes over time were observed in median, ulnar, and peroneal CMAP amplitudes (p > 0.05). CMAP trajectories did not differ between SMA types 2 and 3 (p > 0.05). No significant difference in the change in RULM or HFMSE at any time point was observed between SMA patients with baseline median nerve CMAP < 5 mV and those with CMAP of ≥ 5 mV (p > 0.05). No significant correlations were found between changes in median nerve CMAP and HFMSE or RULM (p > 0.05).DiscussionCMAP amplitudes remained stable during nusinersen treatment, with no differences in trajectories between SMA types 2 and 3. Our findings suggest that while CMAP amplitude correlates with disease severity, it may not serve as a sensitive biomarker of treatment response in adult SMA patients.

P44-F Estimating number of trackable axons in excitability-testing using simulated CMAP scans

Objective To explore a reliable predicator of surgical outcomes of carpal tunnel release(CTR)by exploring the changes of pre-and intraoperative median nerve-abductor pollicis brevis compound muscle action potential(CMAP).Methods Fifteen patients with carpal tunnel syndrome were involved in the study.Electrophysiologic examination was carried out to record CMAP of abductor pollicis brevis muscle at following moments:before CTR right after brachial plexus block,immediate after CTR and tourniquet release,1minute,3 minutes,5 minutes and 7 minutes after tourniquet release.Statistics analysis was done to compare these parameters with preoperative values.Results There were statistically significant changes in both amplitude and latency of the CMAP within 5 minutes after toumiquet release(P<0.05),while not much difference was seen after 5 minutes.While:both the latency and amplitude of CMAP were greatly improved(P<0.05),the improvement of amplitude had more statistical significance(P<0.01).Conclusion CMAP amplitude is a better predictor than CMAP latency to evaluate the effectiveness of median nerve decompression.It is more reliable to carry out electrophysiologic examination at least 5 minutes after tourniquet release. Key words: Carpal tunnel syndrome; Electromyography; Action potentials

Objective To assess the correlations between muscle strength and amplitude of compound muscle action potential(CMAP)with blood potassium level in hypokalemic periodic paralysis after long exercise test(ET).Methods ET of abductor digiti minimi(ADM)was performed on 78 patients with hypokalemic periodic paralysis.Ulnar and median CMAP amplitude,blood potassium level,muscle strength of ADM,palmar interossei muscle and abductor pollicis brevis were measured before and 120 minutes after exercise.The correlations of muscle strength,CMAP amplitude and blood potassium level were analyzed.Results Ulnar CMAP amplitude was(4.6 ±2.7)mV after ET and(9.6 ±3.2)mV before ET(t =16.047,P =0.000)in 78 patients with hypokalemic periodic paralysis,respectively.Median CMAP amplitude was(10.9 ± 4.2)mV after ET and(11.2 ± 3.9)mV before ET(t =0.673,P =0.822),respectively.After ET,muscle strength of ADM decreased in 76 patients,score on MRC was less than Ⅲ in ADM but V in palmar interossei muscle and abductor pollicis brevis in 41 patients,the blood potassium level was tested in 10 of them,which was(3.8 ±0.3)mmol/L before ET and(3.9 ±0.4)mmol/L after ET(t =0.395,P =0.702).Conclusion In patients with hypokalemic periodic paralysis,blood potassium level is not the key factor affecting muscle strength and CMAP amplitude after ET. Key words: Hypokalemic periodic paralysis; Exercise test; Action potentials; Electromyography; Potassium

In motor nerve conduction studies (MNCS), proximal stimulation should give a longer duration and lower amplitude compound muscle action potential (CMAP) due to higher temporal dispersion. Yet the CMAP waveforms at the distal and proximal stimulation sites appear remarkably similar. The objective of this study was to confirm this anomaly and investigate its possible cause by studying the median and ulnar nerves. Recordings from 50 subjects with normal electrodiagnostic studies were reviewed. The conduction velocity (CV) was measured using different points on the negative phase of the CMAP including its peak and baseline crossing. Collision studies were performed in three healthy subjects to measure the dispersion when nerve action potentials (APs) propagated from elbow to wrist. CV was relatively unaffected by the measurement point on the CMAP. The CMAP duration with elbow stimulation increased minimally compared to wrist stimulation. This was inconsistent with the dispersion of the AP from wrist to elbow measured in collision studies. The insignificant change in the CMAP in spite of axon AP dispersion is an enigma. We hypothesize that the terminal conduction time (TCT) (i.e., conduction in terminal axon branches, neuromuscular transmission, etc.) is independent of axon CV, represents a significant portion of the latency, masks AP dispersion, and reduces CMAP dispersion. This yields similar CMAPs with distal and proximal stimulation. The onset latency at the distal stimulation site does not depend on CV. Thus, onset latency and CV may not reflect the conduction properties of the fastest conducting axons.

The diaphragmatic compound motor action potentials (CMAPs) have been used to predict and prevent phrenic nerve injury (PNI) during cryoballoon ablation of right pulmonary veins. We sought to assess factors that influence the amplitude of the surface CMAP recordings. We analyzed CMAPs from consecutive patients undergoing cryoballoon ablation for paroxysmal atrial fibrillation. CMAP recordings were obtained using electrocardiography electrodes positioned in the "modified lead I" method while stimulating the right PN, until loss of capture (ascertained by palpation and fluoroscopy of the right hemi-diaphragm). A total of 55 patients (age 63 ± 11 years; 60% men; body mass index [BMI] 31 ± 6) had adequate CMAP recordings and were included for evaluation of CMAP signals. CMAPs demonstrated 2 distinct components, an early higher amplitude signal (pacing artifact) and a later lower amplitude signal (true diaphragmatic CMAP). There was no significant change in the true CMAP recording amplitude with decrease in stimulus strength (P = 0.1). There was no impact of BMI on CMAP amplitude (P = 0.93). There was a significant phasic respiratory variation in CMAP amplitude with a mean decrease in CMAP amplitude of 10.8% (range: 8-12%) with inspiration lasting an average of 2 beats (P < 0.001). A decrease in CMAP amplitude of >30% was noted in 6 cases (11%) and termination of cryoablation prevented PNI. Diaphragmatic CMAP amplitude is not affected by stimulus strength or BMI. There is a significant respirophasic decrease in CMAP signal amplitude with inspiration. It is important to be aware of this variation to avoid premature termination of cryoablation.