Ulnar Compound Muscle Action Potential Research Articles

Evaluation of Split Hand Syndrome in Early Diagnosis of Amyotrophic Lateral Sclerosis by Nerve Conduction Study as a Diagnostic Tool

Background: Amyotrophic lateral sclerosis (ALS), a degenerative disease of the motor neurons that can present diversly. Needle electromyography (EMG) is the gold standard investigation for the diagnosis of ALS. Split hand syndrome (SHS) demonstrated by nerve conduction study (NCS); a noninvasive tool could be useful in diagnosing ALS. This study aimed to assess SHS by NCS in ALS. Methods: This diagnostic accuracy case-control study included 37 cases of ALS and 37 age and gender-matched controls. Compound muscle action potential (CMAP) and distal motor latency (DML) of median and ulnar nerves and the ratio of median and ulnar CMAP and DML were compared between study groups. The diagnostic validity testing of electrophysiological SHS was also done. Results: The mean age of the ALS and control groups were similar, 39.8±2.7 and 39.3±2.6 years, respectively. Sixteen (43.2%) ALS patients were in 30-59 years age group. Male-female ratio was 5.2. In the ALS group, median-ulnar CMAP ratio was lower and median-ulnar DML ratio was prolonged than the control. The diagnostic efficacy of median-ulnar CMAP ratio and DML ratio were calculated. A median-ulnar CMAP ratio cut-off value ≤1 showed 70% sensitivity, 97% specificity, 96% positive predictive value and 77% negative predictive value. A median-ulnar DML ratio cut-off value ≥1.5 showed 48% sensitivity, 89% specificity, 82% positive predictive value and 65% negative predictive value. Conclusion: NCS demonstrating SHS can be an important tool in the early diagnosis of ALS. J Bangladesh Coll Phys Surg 2024; 42: 350-354

Nerve Transfer After Cervical Spinal Cord Injury: Who Has a “Time Sensitive” Injury Based on Electrodiagnostic Findings?

ObjectiveTo use the ulnar compound muscle action potential (CMAP) to abductor digiti minimi (ADM) to identify the proportion of individuals with cervical spinal cord injury (SCI) who have lower motor neuron (LMN) abnormalities involving the C8-T1 spinal nerve roots, within 3-6 months, and thus may influence the response to nerve transfer surgery. DesignRetrospective analysis of prospectively collected data. Data were analyzed from European Multicenter Study About SCI database. SettingMulti-center, academic hospitals. ParticipantsWe included 79 subjects (age=41.4±17.7, range:16-75; 59 men; N=79), who were classified as cervical level injuries 2 weeks after injury and who had manual muscle strength examinations that would warrant consideration for nerve transfer (C5≥4, C8<3). InterventionsNone. Main Outcome MeasuresThe ulnar nerve CMAP amplitude to ADM was used as a proxy measure for C8-T1 spinal segment health. CMAP amplitude was stratified into very abnormal (<1.0 mV), sub-normal (1.0-5.9 mV), and normal (>6.0 mV). Analysis took place at 3 (n=148 limbs) and 6 months (n=145 limbs). ResultsAt 3- and 6-month post-injury, 33.1% and 28.3% of limbs had very abnormal CMAP amplitudes, respectively, while in 54.1% and 51.7%, CMAPs were sub-normal. Median change in amplitude from 3 to 6 months was 0.0 mV for very abnormal and 1.0 mV for subnormal groups. A 3-month ulnar CMAP <1 mV had a positive predictive value of 0.73 (95% CI 0.69-0.76) and 0.78 (95% CI 0.75-0.80) for C8 and T1 muscle strength of 0 vs 1 or 2. ConclusionA high proportion of individuals have ulnar CMAPs below the lower limit of normal 3- and 6-month post cervical SCI and may also have intercurrent LMN injury. Failure to identify individuals with LMN denervation could result in a lost opportunity to improve hand function through timely nerve transfer surgeries.

MND Phenotypes Differentiation: The Role of Multimodal Characterization at the Time of Diagnosis.

Simple SummaryDiverse motor neuron diseases (MNDs) are associated with distinct survival rates, so their early differentiation is pivotal to gain a more reliable prognosis estimation in clinical and research settings. In this study, we therefore evaluated whether a multimodal characterization approach embedding clinical, cognitive/behavioral, genetic, and neurophysiological data may improve the discrimination of pure/predominant upper motor neuron (pUMN) and pure/predominant lower motor neuron (pLMN) disease forms from classic amyotrophic lateral sclerosis (ALS) already by the time of diagnosis. Our results suggest common cognitive and genetic features across the distinct MND phenotypes, but also demonstrate that highly specific clinical and neurophysiological measures provide valuable tools for an early discrimination between more benign and more aggressive disease forms.Pure/predominant upper motor neuron (pUMN) and lower motor neuron (pLMN) diseases have significantly better prognosis compared to amyotrophic lateral sclerosis (ALS), but their early differentiation is often challenging. We therefore tested whether a multimodal characterization approach embedding clinical, cognitive/behavioral, genetic, and neurophysiological data may improve the differentiation of pUMN and pLMN from ALS already by the time of diagnosis. Dunn’s and chi-squared tests were used to compare data from 41 ALS, 34 pLMN, and 19 pUMN cases with diagnoses confirmed throughout a 2-year observation period. Area under the curve (AUC) analyses were implemented to identify the finest tools for phenotypes discrimination. Relative to ALS, pLMN showed greater lower limbs weakness, lower UMN burden, and progression rate (p < 0.001–0.04). PUMN showed a greater frequency of lower limbs onset, higher UMN burden, lower ALSFRS-r and MRC progression rates (p < 0.001–0.03), and greater ulnar compound muscle action potential (CMAP) amplitude and tibial central motor conduction time (CMCT) (p = 0.05–0.03). The UMN progression rate was the finest measure to identify pLMN cases (AUC = 90%), while the MRC progression rate was the finest tool to identify pUMN (AUC = 82%). Detailed clinical and neurophysiological examinations may significantly improve MNDs differentiation, facilitating prognosis estimation and ameliorating stratification strategies for clinical trials enrollment.

Outcomes after Cervical Duraplasty for Monomelic Amyotrophy (Hirayama Disease): Results of a Case-Control Study of 60 Patients.

Background The optimal management and the role of surgery in monomelic amyotrophy, also known as Hirayama disease (HD), remain controversial. In the largest series of patients with HD managed by cervical duraplasty (CD), this study compares the outcomes between conservative and surgical management. Methods A retrospective case–control study was performed on 60 patients with HD. The cases consisted of 30 patients who underwent CD, and 30 age- and sex-matched controls who managed with long-term collar wear. Clinical improvement was recorded using two patient-reported outcome measures—the Odom's scale and a self-rated hand grip strength score. Median and ulnar compound muscle action potential (CMAP) amplitudes and various magnetic resonance imaging parameters were recorded. Results None of the controls experienced clinical improvement at follow-up; 90% remained status quo at 24.33 ± 9.38 months. Seventy-six percent of the operated patients demonstrated clinical improvement at 29.61 ± 12.78 months, and a majority of them reported moderately better grip strength. The preoperative anteroposterior diameter (APD) of the surgical group improved from 0.74 ± 0.13 to 0.86 ± 0.21 ( p = 0.01), and the cord demonstrated a significant decrease in forward migration on flexion (0.20 ± 0.11 and 0.03 ± 0.07 preoperatively and at follow-up, respectively, p < 0.0001). Patients with clinical improvement demonstrated significantly better mean APD and median and ulnar CMAP values than those who did not improve ( p < 0.0001). The mean cervical alignment did not change significantly at follow-up ( p = 0.13). Conclusions This study shows that CD can significantly alter the clinical course of patients with progressive symptoms of HD. This approach successfully arrests the forward migration of the cervical cord on flexion and promotes morphological recovery of the cord. A majority of the patients undergoing CD demonstrate clinical and electrophysiological improvement at mid-term follow-up.

Safety, Tolerability, and Effect of Nusinersen Treatment in Ambulatory Adults With 5q-SMA.

Objective: To determine the safety and tolerability of nusinersen treatment in ambulatory adults with spinal muscular atrophy (SMA) and investigate the treatment effect on muscle strength, physical function, and motor unit physiology.Methods: Individuals aged 18 years or older with genetically confirmed 5q SMA, three or more copies of the SMN2 gene, and the ability to ambulate 30 feet were enrolled. Safety outcomes included the number of adverse events and serious adverse events, clinically significant vital sign or laboratory parameter abnormalities. Outcome assessments occurred at baseline (prior to the first dose of nusinersen) and then 2, 6, 10, and 14 months post-treatment.Results: Six women, seven men (mean age: 37 ± 11, range: 18–59 years) were included for analyses. The most common side effects were headache and back pain, but overall procedures and treatments were well-tolerated. No serious adverse events were reported. Maximal Voluntary Isometric Muscle Contraction Testing (MVICT) and 6-min walk test (6MWT) both showed overall stability with significant increases at 2, 6, and 10 months for the 6MWT. More consistent significant treatment effects were noted on the Hammersmith Functional Motor Scale Expanded, SMA-Functional Rating Scale, and forced vital capacity. Treatment resulted in progressively increased ulnar compound muscle action potential and average single motor unit potential amplitudes, but motor unit number estimation remained stable.Conclusions: Nusinersen treatment is safe and well-tolerated in ambulatory adults with SMA. Treatment resulted in improved motor function and electrophysiological findings suggest that this improvement may be occurring via improved motor unit reinnervation capacity.

Outcome measures in a cohort of ambulatory adults with spinal muscular atrophy.

With the advent of disease-altering therapies for spinal muscular atrophy (SMA), there is a requirement to better characterize outcome measures, particularly in milder forms of disease. Maximal voluntary isometric contraction testing and 6-minute walk test (6MWT) performed in ambulatory SMA adults as part of the SMA-VALIANT trial were analyzed. Test-retest reliability and correlation with other candidate biomarkers and outcomes were investigated. Maximal voluntary isometric contraction testing and 6MWT showed good test-retest reliability (intraclass correlation coefficient = 0.98 and 0.85, respectively). Maximal voluntary isometric contraction testing and 6MWT demonstrated very strong correlation (r = 0.83, P <. 0001), and each correlated with the SMA Functional Rating Scale (r = 0.7, P < .0001 and r = 0.65, P = .0001, respectively), lean muscle mass (r = 0.68, P < .0001 and r = 0.56, P = .001, respectively), and ulnar compound muscle action potential (r = 0.57, P = .0008 and r = 0.47, P = .008, respectively). Maximal voluntary isometric contraction testing and 6MWT are suitable outcomes for use in ambulatory adults with SMA. Maximal voluntary isometric contraction testing may be preferable because of superior test-retest reliability and closer associations with other outcomes and biomarkers of neuromuscular function.

Far-field potentials in the compound muscle action potential.

It has long been believed that the compound muscle action potential (CMAP) in motor-nerve conduction studies (MCSs) records the action potential beneath the active electrode over the muscle belly. However, recent studies have revealed the contribution of the reference electrode to the CMAP, most prominent in the tibial nerve, followed by the ulnar nerve. This "reference electrode potential" is recorded when the conventional reference electrode distal to the muscle belly is connected to a proximal reference. It must be a far-field potential (FFP) considering its distribution, although the precise mechanism of its generation has not been clarified. The conventional theory of termination of the action potential at the muscle-tendon junction is insufficient. Regarding the ulnar CMAP, interosseous muscles mostly contribute to the FFPs. New understanding of CMAP based on the FFP theory may provide new insights into the interpretation of MCSs and related techniques, including motor unit number estimation.

Abstract TMP40: Secondary Motor Nerve Deficit Correlates With Poorer Outcome in Acute Stroke Patients

Introduction: Anterograde degeneration after stroke leads to secondary injury of peripheral motor nerves. It remains unclear whether this secondary dysfunction affects functional improvement and whether early electrophysiological parameters could possibly predict rehabilitative outcome. Methods: A total of 43 adult patients of middle cerebral artery infarction (MCAI) within 2 weeks after onset was prospectively recruited from January 2016 to December 2017. Ten healthy subjects were recruited as control. All the subjects were investigated by electromyography to record and analyze electrophysiological parameters on admission. All the patients were evaluated by NIHSS, BI, mRS, Fugl-Meyer assessment (FMA) and Alberta Stroke Program Early CT score on admission, then by BI, mRS and FMA in the 6-month follow-up. Multiple regression analysis was used to screen the possible predictive factor for neurological outcome. Results: Twenty-six patients were with massive MCAI and 17 patients with subcortical MCAI. The compound muscle action potential (CMAP) amplitude of median, ulnar, tibial and common peroneal nerves, and motor unit number estimation in abductor of pollicis brevis were significant decreased in the hemiplegic limbs than those in the unaffected limbs and in the healthy controls, and further diminished in massive MCAI compared to those in subcortical MCAI. Fibrillation potentials / positive sharp waves in abductor digiti minimi and tibialis anterior were found in majority of patients, and were more frequently detected in massive MCAI, confirming the motor axonal deficit. CMAP amplitude of the affected ulnar nerves was significantly decreased in patients with unfavorable outcome (mRS&gt;3) 3 and 6 months after attack, shown as an independent predictor for poorer outcome. In addition, the affected ulnar CMAP ≥10.45mV was associated with more than 50% decrement of mRS 6 months post stroke, with sensitivity and specificity of nearly 80%. Conclusions: The data indicated that secondary peripheral motor deficit occurred within 2 weeks after stroke, correlated with severity of the disease. Relatively low CMAP amplitude of hemiplegic ulnar nerve could serve as an independent factor to predict poorer outcome and worse recovery in the 6-month follow-up.

Thoracic outlet syndrome

Thoracic outlet syndrome (TOS) is a well-known disorder, but its definition has been disputed. TOS is differentiated into five distinct disorders: arterial vascular, venous vascular, traumatic neurovascular, true neurologic (TN-TOS), and nonspecific TOS. TN-TOS is caused by compression of the lower plexus (T1>C8 roots and/or lower trunk) by a fibrous band. The most frequent presenting symptoms are insidious-onset atrophy and weakness of the intrinsic hand muscles, predominantly in the thenar eminence and radial digital flexors. Numbness and sensory loss are usually present, mainly in the ulnar forearm, although severe pain or pain/paresthesia proximal to the elbow can occur; however, sensory symptoms or signs can be absent in some patients. Nerve conduction studies are pathognomonic and show the loss or severe attenuation of the sensory nerve action potential (SNAP) of the medial antebrachial cutaneous nerve. Additionally, they show a severely depressed median compound muscle action potential (CMAP) and, subsequently, a depressed ulnar CMAP and SNAP. TN-TOS is a rare disorder, although its incidence may be higher than previously believed. Hirayama disease is an important differential diagnosis. Nonspecific TOS, which is mainly diagnosed by provocative maneuvers, corresponds to the classical concept of TOS. However, this concept is now challenged and the existence of nonspecific TOS is doubted.

Jamar hand-held grip dynamometry in chronic inflammatory demyelinating polyneuropathy

BackgroundFew studies have evaluated the functional and electrophysiological correlates of hand-held grip dynamometry in neuromuscular disease. The practical value of normative values remains uncertain in clinical practice. We aimed to ascertain the value, clinical and electrophysiological correlates, as well as utility of normative values for grip dynamometry, in a cohort of subjects with chronic inflammatory demyelinating polyneuropathy (CIDP). MethodsWe performed a cross-sectional study of 31 prospectively recruited subjects with CIDP, using Jamar hand-held grip dynamometry, conventional clinical assessments and electrophysiology. ResultsGrip dynamometry correlated highly with motor, sensory and functional scores in the upper limbs as well as with global function. There were significant correlations with summated median/ulnar, and ulnar compound muscle action potentials. Patients’ readings were significantly lower than median normative values but comparable to fifth percentile normative figures. ConclusionsJamar grip dynamometry is a reliable measure of global neurological status in patients with CIDP, not limited to upper limb or exclusively motor function. At optimum level of function, CIDP patients had comparable dynamometry recordings to fifth percentile normative values, which may represent a realistic aim for treated subjects with the disorder, with currently available therapies.

Electrophysiological features of hirayama disease

The purpose of this study was to compare the pattern of hand muscle involvement in Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS). We reviewed findings of upper limb nerve conduction studies of 46 HD patients and 60 ALS patients. The findings from 54 healthy subjects were used for comparison. In HD, the ulnar compound muscle action potential (CMAP) amplitude was more severely reduced than the median one, and the reverse pattern was observed in ALS. The mean ulnar/median (U/M) CMAP amplitude ratio was significantly lower in HD (0.64 ± 0.79) and abnormally higher in ALS (2.15 ± 1.77) compared with normal subjects (0.89 ± 0.23). An abnormally low U/M CMAP amplitude ratio (<0.6) was encountered in 34 patients with HD and in 1 with ALS. A U/M CMAP amplitude ratio ≥4.5 or absent median motor response was found only in ALS. Our findings demonstrate different patterns of hand muscle involvement between these two diseases.

Origin of far‐field potentials in the ulnar compound muscle action potential

The compound muscle action potential (CMAP) following ulnar nerve stimulation receives a considerable contribution from far-field potentials (FFPs), although their origin is not entirely clear. We investigated this issue using voluntary contractions. In 7 control subjects, we placed multiple recording electrodes over the motor points of ulnar-innervated muscles. We asked the subjects to perform a weak movement corresponding to the action of each muscle, and identified the single motor unit potentials (MUPs) from that muscle. We summed the MUPs from each individual muscle and reconstructed the CMAPs. The reconstructed CMAPs coincided well with the actual ones. The N1, P1, and early N2 components of the FFPs were generated primarily by palmar, but also by dorsal, interosseous muscles. The abductor digiti minimi muscle usually generated positive-negative biphasic FFPs, and the negative FFP generated the late N2 component. These results should prompt a revision of the theory of FFP generation.

Ulnar Nerve Conduction Study of the First Dorsal Interosseous Muscle in Korean Subjects

ObjectiveTo derive normative values for ulnar nerve conduction study of the active recording electrode on the first dorsal interosseous muscle (FDI) and the reference electrode on the proximal phalanx of the thumb.MethodUlnar nerve motor conduction study with FDI and abductor digiti minimi muscle (ADM) recording was performed in 214 hands of 107 healthy subjects. Ulnar NCS was performed with 2 different recording electrode montages (ADM-base of 5th finger; FDI-thumb) and differences in latency and amplitude were compared. Using this technique, the initial positivity of ulnar compound muscle action potential (CMAP) was not observed in any response with FDI recording.ResultsThe maximal values for distal motor latency to the ADM and FDI muscle were 3.8 ms and 4.4 ms, respectively. The maximal difference of distal motor latency between the bilateral FDI recordings was 0.6 ms. The maximal ipsilateral latency difference between ADM and FDI was 1.4 ms.ConclusionPlacement of the reference electrode on the thumb results in a CMAP without an initial positivity and the normative values obtained may be useful in the diagnosis of ulnar neuropathy at the wrist.

Electrophysiological characteristics of juvenile muscular atrophy of distal upper extremity ( Hirayama's disease)

Objective The purpose of this study was to retrospectively evaluate the electrophysiological characteristics of Hirayama disease. Methods Electrophysiological records of 77 patients with a diagnosis of Hirayama disease were reviewed. We analyzed the amplitude of compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) as well as the F wave latency and frequency of median and ulnar nerves. We also evaluated the changes of needle electromyography. Results Of the 77 patients, 74 were male and 3 female. Mean age of onset was ( 17.7 ± 2.6 ) years and mean disease duration (28.2 ± 25.7 ) months. 57 of the 77 patients showed clinical presentation of unilateral involvement. Reduced ulnar CMAP amplitude was found prodominantly. Abnormal F wave frequency was found in the majority of the patients in both median and ulnar nerves and there was also correlation between F wave frequency and amplitude of CMAP. Sensory conduction studies were normal. In the needle EMG, neurogenic changes were found in both upper limbs in 67 cases and the remaining 10 patients were unilateral involved. Denervation was found in the C7-T1 myotomes in all of the 77 patients. Among them, 15 also showed C5, C6 involvement with different extent. Conclusion In this study, the most obvious electrophysiological abnormality was reduced F wave frequency in both median and ulnar nerves followed by reduced ulnar CMAP amplitude. Although most patients showed unilateral involvement clinically,needle EMG found 87% had bilateral neurogenic changes. Although C7, C8, T1 myotomes were mainly damaged in Hirayama disease, C5,C6 was also involved in around 1/5 of the patients. Key words: Muscular atrophy; Upper extremity; Electromyography; F wave

Compound muscle action potential and motor function in children with spinal muscular atrophy

Reliable outcome measures that reflect the underlying disease process and correlate with motor function in children with SMA are needed for clinical trials. Maximum ulnar compound muscle action potential (CMAP) data were collected at two visits over a 4-6-week period in children with SMA types II and III, 2-17 years of age, at four academic centers. Primary functional outcome measures included the Modified Hammersmith Functional Motor Scale (MHFMS) and MHFMS-Extend. CMAP negative peak amplitude and area showed excellent discrimination between the ambulatory and non-ambulatory SMA cohorts (ROC = 0.88). CMAP had excellent test-retest reliability (ICC = 0.96-0.97, n = 64) and moderate to strong correlation with the MHFMS and MHFMS-Extend (r = 0.61-0.73, n = 68, P < 0.001). Maximum ulnar CMAP amplitude and area is a feasible, valid, and reliable outcome measure for use in pediatric multicenter clinical trials in SMA. CMAP correlates well with motor function and has potential value as a relevant surrogate for disease status.

The Nature of the Relationship Between Smoking and Ulnar Neuropathy at the Elbow

To confirm that smoking increases the risk for ulnar neuropathy at the elbow and to investigate potential mechanisms for that increased risk. Prospective case-control study featuring the recruitment of 100 subjects with upper-limb neurologic symptoms: 50 meeting (cases) and not meeting (controls) electrodiagnostic criteria for ulnar neuropathy at the elbow. Known risk factors for ulnar neuropathy at the elbow, preferred smoking hand, and upper-limb joint angles during preferred smoking posture were recorded. Subjects with ulnar neuropathy at the elbow reported increased smoking when compared with the control group, but there was no agreement between ulnar neuropathy at the elbow side and preferred smoking hand or group differences in joint angles during preferred smoking posture. Ulnar neuropathy at the elbow occurred more frequently on the left regardless of hand dominance (P = 0.007). Independent risk factors included age, male sex, and smoking (in pack-years), demonstrating odds ratios (95% confidence intervals) of 1.054 (1.015-1.095), 4.41 (1.75-11.16), and 1.035 (1.001-1.070), respectively. Smoking also correlated negatively with above-elbow ulnar compound muscle action potential, across-elbow conduction velocity, and conduction block. Smoking is associated with increased risk for ulnar neuropathy at the elbow, and the dose-response effect between smoking and electrophysiologic ulnar measures associated with ulnar neuropathy at the elbow severity increases the likelihood that the relationship is one of cause and effect. However, the data do not suggest that a mechanical explanation related to repetitive elbow flexion is likely.

34. The mechanism of the far-field potentials contaminating ulnar compound muscle action potentials

34. The mechanism of the far-field potentials contaminating ulnar compound muscle action potentials

Does retrograde axonal atrophy really occur in carpal tunnel syndrome patients with normal forearm conduction velocity?

Objective The cause of decreased median forearm motor conduction velocity (FMCV) in carpal tunnel syndrome (CTS) is best ascribed to retrograde axonal atrophy (RAA); however, the relationships between the occurrence of RAA and electrophysiological or clinical severity remains controversial. We attempt to determine whether RAA really occurs in CTS patients with normal median FMCV and to investigate any relationships between RAA and severity of compression at the wrist. Methods Consecutive CTS patients were enrolled and age-matched volunteers served as controls. We performed conventional nerve conduction studies (NCS) and measured median and ulnar distal motor latencies (DML), FMCV, compound muscle action potential (CMAP) amplitudes, distal sensory latencies (DSL), and sensory nerve action potential (SNAP) amplitudes. Furthermore, palmar median stimulation was done to calculate the wrist–palm motor conduction velocity (W-P MCV). Patients included for analysis should have normal FMCV and needle examination. We compared each electrodiagnostic parameters between the patient group and controls. Results The mean±SD of the W-P MCV for patients and controls were 33.26±6.74 and 52.14±5.85 m/s and those of median FMCV were 55.26±3.56 and 57.82±3.9 m/s, respectively. There was a significant reduction in the W-P MCV (36.2%, P<0.00001), significant decrease in the median FMCV (4.43%, P<0.00001) and SNAP amplitudes, and an increase of the DML and DSL in the patient group ( P<0.00001) compared to the controls; however, there were no differences in median and ulnar CMAP amplitudes, ulnar FMCV and DML between the controls and patients. Conclusions RAA and relatively slowed median FMCV do occur in CTS patients with normal median FMCV, regardless of severity of clinical manifestations and electrophysiological abnormalities. Significance This article provides new information for research of the electrophysiological changes of the proximal nerve part at distal injury.

Optimal distance for segmental nerve conduction studies revisited.

In 1972, Maynard and Stolov showed that the experimental error in calculating nerve conduction velocity (NCV) depends on errors of latency and distance measurements. Their data suggested that a minimum distance of 10 cm should be used when calculating NCV because of an increase in error >/= 25% at shorter distances. The object of this study was to reestablish the minimum distance using current technology. Twenty physicians measured the proximal and distal onset latencies of the same stored ulnar compound muscle action potentials, as well as the forearm skin distance. The mean and standard deviation of the errors in conduction time and distance were determined. A spreadsheet was constructed, determining the error in NCV for a variety of distances and NCVs. The average conduction time between proximal and distal stimulation was 3.23 ms, with a standard deviation of 0.09 ms. The mean distance measurement was 212.6 +/- 2.1 mm. The errors in NCV were significantly less than previously reported. The experimental error increased as distance decreased, reaching 20% with distances less than 6 cm. The latency error accounted for 71% of the total experimental error, as opposed to 90% in the previous study. With advances in electrodiagnostic equipment, NCV can reasonably be calculated at distances less than 10 cm, perhaps as low as 5-6 cm.

Changes in nerve conduction velocity across the elbow due to experimental error.

One diagnostic criterion for ulnar nerve mononeuropathy at the elbow (UNE) is a decrease in across-elbow nerve conduction velocity (NCV) > 10 m/s compared to the forearm segment. Distance and latency measurement errors are an inherent part of NCV calculations. Twenty electromyographers measured the latencies of stored ulnar compound muscle action potentials and measured the forearm and across-elbow distances along the ulnar nerve. Based on previously published equations, experimental error in NCV was calculated for various NCVs. The mean distances and standard deviations for the forearm and elbow segments were 212.5 +/- 2.1 mm and 86.7 +/- 4.2 mm, respectively. For an NCV of 55 m/s, a difference of 14 m/s between the two segments can occur from measurement error alone. Distance measurements about the elbow are fraught with interobserver errors rendering the resultant NCV of that segment of limited value as a sole criterion for the diagnosis of UNE.