Correlation between Elbow Flexor Muscle Strength and Needle Electromyography Parameters after Musculocutaneous Nerve Injury / 法医学杂志

OBJECTIVES@#To explore the changes of elbow flexor muscle strength after musculocutaneous nerve injury and its correlation with needle electromyography (nEMG) parameters.@*METHODS@#Thirty cases of elbow flexor weakness caused by unilateral brachial plexus injury (involving musculocutaneous nerve) were collected. The elbow flexor muscle strength was evaluated by manual muscle test (MMT) based on Lovett Scale. All subjects were divided into Group A (grade 1 and grade 2, 16 cases) and Group B (grade 3 and grade 4, 14 cases) according to their elbow flexor muscle strength of injured side. The biceps brachii of the injured side and the healthy side were examined by nEMG. The latency and amplitude of the compound muscle action potential (CMAP) were recorded. The type of recruitment response, the mean number of turns and the mean amplitude of recruitment potential were recorded when the subjects performed maximal voluntary contraction. The quantitative elbow flexor muscle strength was measured by portable microFET 2 Manual Muscle Tester. The percentage of residual elbow flexor muscle strength (the ratio of quantitative muscle strength of the injured side to the healthy side) was calculated. The differences of nEMG parameters, quantitative muscle strength and residual elbow flexor muscle strength between the two groups and between the injured side and the healthy side were compared. The correlation between elbow flexor manual muscle strength classification, quantitative muscle strength and nEMG parameters was analyzed.@*RESULTS@#After musculocutaneous nerve injury, the percentage of residual elbow flexor muscle strength in Group B was 23.43% and that in Group A was 4.13%. Elbow flexor manual muscle strength classification was significantly correlated with the type of recruitment response, and the correlation coefficient was 0.886 (P<0.05). The quantitative elbow flexor muscle strength was correlated with the latency and amplitude of CMAP, the mean number of turns and the mean amplitude of recruitment potential, and the correlation coefficients were -0.528, 0.588, 0.465 and 0.426 (P<0.05), respectively.@*CONCLUSIONS@#The percentage of residual elbow flexor muscle strength can be used as the basis of muscle strength classification, and the comprehensive application of nEMG parameters can be used to infer quantitative elbow flexor muscle strength.

Reference values for nerve conduction studies in healthy newborns, infants and children in Philippine Children's Medical Center

@#<p style="text-align: justify;"><strong>BACKGROUND:</strong> Nerve conduction studies play a diagnostic role in the clinical evaluation of neuromuscular disorders in children. Reference ranges define the expected parameter values in disease-free children.</p><p style="text-align: justify;"><strong>OBJECTIVE:</strong> To propose reference values for sensory and motor nerve conduction and late responses in upper and lower limb peripheral nerves in Filipino children 5 years and below.</p><p style="text-align: justify;"><strong>METHODS</strong>: Sensory nerve conduction studies on median, ulnar, superficial peroneal, and sural nerves and motor nerve conduction and late response studies on median, ulnar, peroneal and posterior tribal nerves were done using standardized techniques among 100 healthy Filipino children.</p><p style="text-align: justify;"><strong>RESULTS:</strong> Subjects were stratified according to age groups. Reference values for the following parameters: (1) sensory conduction velocity and amplitude; (2) motor conduction velocity, amplitude and latency at distal sites;  (3) F-wave latency; and (4) H-reflex latency were summarized. These were expressed as mean ±standard deviation or median (range) for values that follow Gaussian and non-Gaussian distributions. The 5th and 95th percentile values were likewise reported. Age had direct correlation with various nerve conduction parameters. Height was directly correlated with F-wave parameters of median, ulnar and peroneal nerves but not posterior tribal nerve.</p><p style="text-align: justify;"><strong>CONCLUSIONS</strong>: Reference standards for nerve conduction studies of commonly tested nerves of Filipino children are presented. Values are comparable to reference ranges elsewhere except for the H-reflex latency which is higher in this study.</p>

Clinical Significance of Repetitive Compound Muscle Action Potentials in Patients with Myasthenia Gravis: A Predictor for Cholinergic Side Effects of Acetylcholinesterase Inhibitors

BACKGROUND AND PURPOSE: Acetylcholinesterase inhibitors (AChEIs) are widely used to treat myasthenia gravis (MG). Although AChEIs are usually tolerated well, some MG patients suffer from side effects. Furthermore, a small proportion of MG patients show cholinergic hypersensitivity and cannot tolerate AChEIs. Because repetitive compound muscle action potentials (R-CMAPs) are an electrophysiologic feature of cholinergic neuromuscular hyperactivity, we investigated the clinical characteristics of MG patients with R-CMAPs to identify their clinical usefulness in therapeutic decision-making. METHODS: We retrospectively reviewed the clinical records and electrodiagnostic findings of MG patients who underwent electrodiagnostic studies and diagnostic neostigmine testing (NT). RESULTS: Among 71 MG patients, 9 could not tolerate oral pyridostigmine bromide (PB) and 17 experienced side effects of PB. R-CMAPs developed in 24 patients after NT. The highest daily dose of PB was lower in the patients with R-CMAPs (240 mg/day vs. 480 mg/day, p<0.001). The frequencies of PB intolerance and side effects were higher in the patients with R-CMAPs than in those without R-CMAPs [37.5% vs. 0% (p<0.001) and 45.8% vs. 12.8% (p=0.002), respectively]. The MG Foundation of America postintervention status did not differ significantly between MG patients with and without R-CMAPs, and the response to immunotherapy was also good in both groups. CONCLUSIONS: Side effects of and intolerance to AChEIs are more common in MG patients with R-CMAPs than in those without R-CMAPs. AChEIs should be used carefully in MG patients with R-CMAPs. The presence of R-CMAPs after NT may be a good indicator of the risks of PB side effects and intolerance.

Repetitive nerve stimulation in amyotrophic lateral sclerosis / 西安交通大学学报(医学版)

ABSTRACT:Objective To evaluate the features and related factors of decremental response in amyotrophic lateral sclerosis (ALS)patients to low-frequency repetitive nerve stimulation (RNS)in proximal nerves.Methods We performed RNS studies in proximal axillary and accessory nerves with recording in deltoid and trapezius mus-cle respectively in 87 ALS patients.Decremental compound muscle action potential (CMAP)and related factors were analyzed prospectively,and abnormal group of decremental response in ALS patients was compared with 39 pa-tients with myasthenia gravis.Results ① Abnormal decremental responses were found in 43.7% and 49.4% of ALS patients with deltoid and trapezius muscle recording respectively.They were found more frequent in trapezius muscle than those of deltoid muscle.② There was no relationship of decremental response with gender,age,onset or course of disease,ALSFRS-r scores,or rate of disease progression in ALS patients.③ There was significant rela-tionship between decremental response and fluctuating muscle weakness.Decremental responses decreased more ob-viously in ALS patients with fluctuating muscle weakness than in those with nonfluctuating muscle weakness.④ Dec-remental responses were greater in patients with myasthenia gravis than that in ALS patients.Conclusion Decre-mental response with proximal muscle recording is not an uncommon feature in ALS patients;therefore,it should not be treated as a criterium to rule out ALS.Abnormal decremental response of trapezius muscle is found more fre-quent than that of deltoid muscle.Decremental response range in patients with myasthenia gravis is significantly lar-ger than that in ALS patients.One should be more careful when diagnosing ALS patients with fluctuating muscle weakness and abnormal decremental response.

Variety of the Wave Change in Compound Muscle Action Potential in an Animal Model

STUDY DESIGN: Animal study. PURPOSE: To review the present warning point criteria of the compound muscle action potential (CMAP) and investigate new criteria for spinal surgery safety using an animal model. OVERVIEW OF LITERATURE: Little is known about correlation palesis and amplitude of spinal cord monitoring. METHODS: After laminectomy of the tenth thoracic spinal lamina, 2-140 g force was delivered to the spinal cord with a tension gage to create a bilateral contusion injury. The study morphology change of the CMAP wave and locomotor scale were evaluated for one month. RESULTS: Four different types of wave morphology changes were observed: no change, amplitude decrease only, morphology change only, and amplitude and morphology change. Amplitude and morphology changed simultaneously and significantly as the injury force increased (p<0.05) Locomotor scale in the amplitude and morphology group worsened more than the other groups. CONCLUSIONS: Amplitude and morphology change of the CMAP wave exists and could be the key of the alarm point in CMAP.

Effects of botulinum toxin combined with treadmill training on motor and gastrocnemius function after spinal cord injury / 中华物理医学与康复杂志

Objective To observe the effects of botulinum toxin A(BTX-A) injection combined with treadmill training on motor and gastrocnemius function in rats after spinal cord injury (SCI),so as to develop a possible treatment.Methods A total of 48 female Sprague-Dawley rats were randomly divided into four groups(n =12 in each):a control group which received normal saline injection(group Con-NS),an exercise group with normal saline injection(group Ex-NS),the other control group with BTX-A injection(group Con-BTX)and an exercise group which also received BTX-A injection(group Ex-BTX).All rats were subjected to incomplete SCI modelling using Allen's method.Each group then had l0 members left because of death or significant weight loss.After SCI modelling,BTX-A or normal saline were injected to rats' gastrocnemius,followed by weight support treadmill training(BWSTT) on days 7 through 35 days for the two exercise groups.Motor function was evaluated using inclined plane test before and 2 days,1,2,3,4 and 5 weeks after the injury.All rats were sacrificed 35 days after the surgery.Digit Abduction Scoring(DAS) and electrophysiological testing were performed prior to sacrifice,and the general form and the wet weight of gastrocnemius were observed after resection.Results No significant differences in the inclined plane angle among 4 groups were detected before injury and 2 days afterward (P ＞ 0.05).At the 2nd-Sth week,however,the inclined plane angles in group Ex-NS were significantly higher than those in group Con-NS (P ＜ 0.05).Those of group Ex-NS were also significantly higher than group Ex-BTX 2-5 weeks after injury (P ＜ 0.05).No significant differences were detected between group Con-BTX and group Ex-BTX,as well as group Con-NS and group Ex-BTX at each time point (P ＞ 0.05).And the average DAS score in group Con-BTX and group Ex-BTX was 0,while that of Con-NS group and group Ex-NS were both 4.There were no significant differences between the two normal saline injection groups (P ＜ 0.05),nor between the two BTX-A injection groups (P ＜ 0.05).However,the average DAS scores in the Con-BTX and Ex-BTX groups were significantly higher than the Con-NS and Ex-NS groups (P ＜ 0.05).No significant atrophy of gastrocnemius muscles were observed in the Con-NS group or Ex-NS group,and as would be expected,the muscles in group Ex-NS were thicker on average than those in group Con-NS.Significant atrophy was observed in group Con-BTX and group Ex-BTX.Moreover,the muscle wet weight was significantly higher in group ExNS than group Con-NS (P ＜ 0.05).Compared with group Con-NS and group Ex-NS,the muscle wet weight was significantly lower in group Con-BTX and group Ex-BTX (P ＜ 0.05).No significant differences in the latency of the compound muscle action potential (CAMP) were detected among 4 groups (P ＞0.05),but the CAMP amplitude was significantly less in the control groups than in the exercise groups.(P ＜0.05).Conclusions Exercise training can significantly improve motor and skeletal muscle function in SCI rats,but BTX-A injection can inhibit the improvement.

Clinical and Electrophysiologic Responses to Acetylcholinesterase Inhibitors in MuSK-Antibody-Positive Myasthenia Gravis: Evidence for Cholinergic Neuromuscular Hyperactivity

BACKGROUND AND PURPOSE: Patients with muscle-specific tyrosine kinase (MuSK) antibody (MuSK-Ab)-positive myasthenia gravis (MG) show distinct responses to acetylcholinesterase inhibitors (AChEIs). Although clinical responses to AChEIs in MuSK-Ab MG are reasonably well known, little is known about the electrophysiologic responses to AChEIs. We therefore investigated the clinical and electrophysiologic responses to AChEIs in MuSK-Ab-positive MG patients. METHODS: We retrospectively reviewed the medical records and electrodiagnostic findings of 17 MG patients (10 MuSK-Ab-positive and 7 MuSK-Ab-negative patients) who underwent electrodiagnostic testing before and after a neostigmine test (NT). RESULTS: The frequency of intolerance to pyridostigmine bromide (PB) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (50% vs. 0%, respectively; p=0.044), while the maximum tolerable dose of PB was lower in the former (90 mg/day vs. 480 mg/day, p=0.023). The frequency of positive NT results was significantly lower in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (40% vs. 100%, p=0.035), while the nicotinic side effects of neostigmine were more frequent in the former (80% vs. 14.3%, p=0.015). Repetitive compound muscle action potentials (R-CMAPs) developed more frequently after NT in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (90% vs. 14.3%, p=0.004). The frequency of a high-frequency-stimulation-induced decrement-increment pattern (DIP) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (100% vs. 17.7%, p=0.003). CONCLUSIONS: These results suggest that MuSK-Ab-positive MG patients exhibit unique and hyperactive responses to AChEIs. Furthermore, R-CMAP and DIP development on a standard AChEI dose may be a distinct neurophysiologic feature indicative of MuSK-Ab-positive MG.

Changes of Compound Muscle Action Potential in Short-term Steroid Therapy for Compression Injury of Rat Sciatic Nerve

0.05).CONCLUSION: This study did not show any therapeutic effect of short-term administration of steroids on injured rat sciatic nerve. Further studies are needed.

Comparison between Clinical Disabilities and Electrophysiological Values in Charcot-Marie-Tooth 1A Patients with PMP22 Duplication

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth disease (CMT) type 1A (CMT1A) is the demyelinating form of CMT that is significantly associated with PMP22 duplication. Some studies have found that the disease-related disabilities of these patients are correlated with their compound muscle action potentials (CMAPs), while others have suggested that they are related to the nerve conduction velocities. In the present study, we investigated the correlations between the disease-related disabilities and the electrophysiological values in a large cohort of Korean CMT1A patients. METHODS: We analyzed 167 CMT1A patients of Korean origin with PMP22 duplication using clinical and electrophysiological assessments, including the CMT neuropathy score and the functional disability scale. RESULTS: Clinical motor disabilities were significantly correlated with the CMAPs but not the motor nerve conduction velocities (MNCVs). Moreover, the observed sensory impairments matched the corresponding reductions in the sensory nerve action potentials (SNAPs) but not with slowing of the sensory nerve conduction velocities (SNCVs). In addition, CMAPs were strongly correlated with the disease duration but not with the age at onset. The terminal latency index did not differ between CMT1A patients and healthy controls. CONCLUSIONS: In CMT1A patients, disease-related disabilities such as muscle wasting and sensory impairment were strongly correlated with CMAPs and SNAPs but not with the MNCVs or SNCVs. Therefore, we suggest that the clinical disabilities of CMT patients are determined by the extent of axonal dysfunction.

Value of magnetic stimulation in the non-invasive diagnosis of St radiculopathy / 中华物理医学与康复杂志

Objective To explore the value of a new electrodiagnostic approach for evaluating motor nerve root function in patients with S1 radiculopathy. Methods Thirty healthy subjects and 30 patients with clinical mani-festations of unilateral S1 radiculopathy were recruited. Bilateral compound muscle action potentials evoked by magnetic stimulation of the first sacral nerve root were recorded from the soleus of all the subjects. F wave and M responses to electrical stimulation of the bilateral tibial nerves at the popliteal fossa were also recorded. The peripheral motor conduction time (PMCT) and the motor root conduction time (MRCT) were calculated and compared between the two groups. In addition, needle electromyographic examination (NEE) was performed on the affected side to detect any possible EMG abnormalities. Results The norm established with the normal subjects was 3.45±0.39 ms for the MRCT, and 0.28±0.15 ms for the inter-side difference in the MRCT. In the 30 patients, the mean MRCT and PMCT values on the affected side were prolonged. Of the 23 patients who received NEE, 6 had EMG abnormalities. The agreement between the NEE and MRCT diagnoses was 82.6%. Conclusion MRCT can be used reliably for non-invasive estimation of motor nerve root function and to help diagnose the S1 radiculopathy.

Comparison of measurement of phrenic nerve conduction time and evoked compound muscle action potential of diaphragm with surface electrodes and oesophageal electrodes / 中国实用内科杂志

Objective To evaluate the feasibility of measuring phrenic nerve conduction time(PNCT)and elicited compound muscle action potential(CMAP)of diaphragm with surface electrodes.Methods PNCT and amplitude of diaphragm CMAP elicited by unilateral magnetic stimulation(UMS)of the phrenic nerve were measured with surface electrodes and the results were compared with those measured with oesophageal electrodes.Results (1)PNCT measured with oesophageal electrode was similar to those measured with surface electrode;the amplitude of CMAP measured with oesophageal electrode was higher than those with surface electrode.(2)There was a significant relationship between the amplitudes of right CMAP measured with oesophageal electrode and those with surface electrodes,whereas there was no such relationship for the left side.(3)The PNCT and the amplitude of CMAP were not related to age,height,weight and perimeter of abdomen no matter measured with oesophageal or surface electrodes.Conclusion Surface electrodes is a useful and noninvasive method to evaluate the function of phrenic nerve and diaphragm.

Dorsal Ulnar Cutaneous Nerve Conduction Study in Entrapment Ulnar Neuropathy at the Elbow

OBJECTIVE: To evaluate the electrophysiologic findings of the dorsal ulnar cutaneous nerve (DUCN) in ulnar neuropathy at the elbow and to correlate the sensory nerve action potential (SNAP) amplitude of DUCN to those of ulnar compound muscle action potential (CMAP) and SNAP. METHOD: The subjects were 39 patients diagnosed as ulnar neuropathy at the elbow. Electrophysiologic classification consisted of 3 groups: conduction block (CB); conduction block and axonal degeneration (CBAD); axonal degeneration (AD). Findings of DUCN conduction study were evaluated according to the electrophysiologic classification. The amplitude of DUCN was correlated to those of CMAP and SNAP. RESULTS: The DUCN conduction study was normal in all cases of CB (4 cases), but was abnormal in 21 cases of CBAD (23 cases) and in 10 cases of AD (12 cases). Even in the cases with AD, 4 cases showed normal DUCN potentials. Correlations of DUCN to ulnar SNAP and CMAP were r=0.48, (p<0.01) and r=0.33, (p<0.05), respectively. CONCLUSION: Findings of DUCN may be related to the fascicular involvement of the ulnar nerve at the elbow. Although it is possible for the DUCN to be spared in ulnar neuropathy at the elbow, electrophysiologic measurement of the DUCN response remains useful, but only in those cases where it is abnormal, which suggests the lesion to be at a more proximal site.

Establishment of the normative ranges for nerve conduction values of distal compound muscle action potential / 西安交通大学学报(医学版)

Objective To establish the normative ranges for nerve conduction values of distal compound muscle action potential(CMAP) latency and amplitude and to provide evidence for diagnosing peripheral neuropathy.Methods A total of 245 normal volunteers were recruited,and nerve conduction study was carried out on median nerve,ulnar nerve,tibial nerve and peroneal nerve.The distal latency and amplitude were analyzed.The data collected were tabulated and analyzed based on age,sex and weight in the EXCEL and SPSS systems.Results Gender,weight and sidedness had no effects on CMAP distal latency and amplitude.However,age had a significant effect on CMAP amplitude and median nerve distal latency.This age effect was more obvious for people around 40 years old.Distal latency was prolonged and amplitude was decreased with age increasing.Conclusion It is reasonable and clinically practicable to establish the normative ranges of distal CMAP according to two age groups: above and below 40 years old.

Changes in Compound Muscle Action Potentials according to the Dilution Volume of the Botulinum Toxin Type A

OBJECTIVE: To know if changes in compound muscle action potential (CMAP) of human extensor digitorum brevis (EDB) muscle can be enhanced by increase in dilution volume of botulinum toxin type A. METHOD: In 11 healthy volunteers, 2.5 U of botulinum toxin (Botox (R) , Allergen Inc.) in a volume of 0.1 ml normal saline was injected in EDB muscle and the same dose with the dilution volume of 0.5 ml was injected in the opposite side. We measured the pre- and post-injection M-wave amplitude and area of EDB muscle. RESULTS: The mean post/pre injection amplitude ratio of CMAP were 0.49+/-0.21 with the 0.1 ml of dilution volume and 0.40+/-0.12 with the 0.5 ml of dilution volume. The mean post/pre injection area ratio of CMAP were 0.51 0.18 with the 0.1 ml of dilution volume and 0.44+/-0.15 with the 0.5 ml of dilution volume. There was no significant difference between the two dilution volumes. CONCLUSION: Five fold increase in dilution volume did not enhance the paralyzing effect of botulinum toxin type A in human EDB muscles.

Dose-dependent Responses to Botulinum Toxin A Injection on Compound Muscle Action Potential Amplitude and Electromyography: Local and Distant Effects

OBJECTIVE: The purpose of this study was to investigate the dose-dependent responses to botulinum toxin A (BTX-A) injection on compound muscle action potential (CMAP) amplitude and needle electromyography (EMG) in local and distant muscles. METHOD: The BTX-A (Botox , Allergan Co.) was injected to the left tibialis anterior (TA): 2, 4, 6, 8 U for each 4 Sprague-Dawley rats; 5, 10, 15, 20 U for each 2 rats. The sciatic nerve conduction and needle EMG were performed in the right and left TA immediately before BTX-A injection, on 2 days after injection, weekly for 1 to 10 weeks, and then monthly for 4 months. RESULTS: The range of dose-dependent maximal paralysis of the injected muscle was from 94% to 99.2% on 7 days after injection. With the lapse of time, the amplitudes in the left sciatic nerve conduction recovered, the abnormal spontaneous activities disappeared, and the power in spectral analysis of motor unit action potential increased. The range of dose-dependent reductions of the CMAP amplitude of the right TA was from 41.8% to 69.9% in the distant muscle, but there was no abnormal spontaneous activity in needle EMG study. As higher doses of BTX-A were injected, the degree of amplitude reduction became larger and the duration of amplitude reduction became longer in both local and distant TA muscles. CONCLUSION: We observed the dose-dependent muscle paralysis with injection of BTX-A. The systemic effects by local injection were induced and the durations of local and systemic effects were proportional to the BTX-A dosage.

Changes of Compound Muscle Action Potentials Related to Voluntary Muscle Contraction and Alteration of Muscle Length in Peripheral Neuropathy

OBJECTIVE: To investigate waveform changes of compound muscle action potentials (CMAPs) related to voluntary muscle contraction and alteration of muscle length and to evaluate the effect of peripheral neuropathy on temporal and spatial summations of CMAPs. METHOD: The influence of voluntary muscle contraction and alteration of muscle length on CMAP was studied in 37 median nerves of 21 patients with median neuropathy. RESULTS: In patients with no apparent axonopathy, temporal summation was partially disturbed without significant change of spatial summation. Shortening of muscle length or voluntary contraction produced a physiologic improvement of spatial and temporal summations. There was a decrease in temporal and spatial summations, more prominent in temporal summation, with lengthening of the muscle. In axonopathy, spatial summation was markedly deteriorated with partial reduction of temporal summation. Spatial summation was not affected by the change of muscle length or voluntary contraction. Temporal summation was improved by muscle shortening or voluntary contraction and was decreased by muscle lengthening. CONCLUSION: Peripheral neuropathy has an effects on physiological spatial and temporal summations of CMAPs. Temporal summation is preferentially decreased in cases without axonopathy. When axonopathy is apparent, spatial summation is profoundly disturbed with partial reduction of temporal summation.

Waveform Changes of Compound Muscle Action Potentials Related to Voluntary Muscle Contraction and Alteration of Muscle Length

The influence of voluntary muscle contraction and alteration of muscle length on compound muscle action potential (CMAP) was studied in 20 healthy volunteers. The CMAPs were evoked by a supramaximal stimulation and recorded by a surface electrode array. Onset latencies were not significantly changed regardless of the muscle length and contraction. On shortening of the muscle there was a decrease in an area and duration of CMAP with no significant changes in an amplitude. During muscle contractions, there was an increase in amplitude and a decrease in area and duration. On a lengthening of the muscle with relaxation, the amplitude of CMAP decreased with an increased area and duration. During a voluntary contraction, there was a decrease in amplitude, area, and duration. The results are considered due to a peripheral factor such as an alteration of temporal or spatial summation rather than a central mechanism. We conclude that in nerve conduction studies, it is important to monitor the finger position and muscle relaxation to differentiate the waveform changes from the muscle length or contraction and those from the nerve lesions.

Titration of Phenol Nerve Block Effects on Peripheral Nerves

Chemical neurolysis can be an extremely effective intervention for reducing spasticity. Phenol nerve block as a method of chemical neurolysis has been used over 40 years, nevertheless, many clinicians remain reluctant to perform this procedure. This is largely due to the fear of its side effects and complications such as excessive muscle weakness or increased spasticity of antagonistic muscles. The purpose of this study was to titrate the nerve block effects of phenol with different concentrations and different volumes of the phenol solution. Left tibial nerves of forty eight adult rabbits were injected with phenol solution of different concentrations(5%, 4%, 3%) and volumes(0.3 ml, 0.2 ml, 0.1 ml) into the epineural sheath. Nerve conduction study of the gastrocnemius muscle was performed before and after the nerve blocks(1day, 1week, 2weeks, 4weeks, 8weeks). The proportion of compound muscle action potential(CMAP) amplitudes and areas before and after the nerve blocks was used for the evaluation of nerve block effect. There was a statistically significant difference in the proportion among three volumes of phenol solution(p0.05) although the higher concentration of phenol solution showed the tendency for smaller proportion. The area of histological degeneration appeared at 2 weeks following nerve block alongside the perineurium. The depth of degeneration area of nerve fascicle varied according to the distance from injection point. These data suggest that the nerve block effect of phenol can be titrated more easily with the volume of phenol solution rather than the concentration until 8 weeks after the nerve block. The variation of the extent of degeneration with different volumes of phenol solution seems to be the mechanism for the titration.