Sural nerve conduction parameters in normal subjects related to age, gender, temperature, and height: a reappraisal

Age-Related Changes in Neurologic Examination and Sensory Nerve Amplitude in the General Population: Aging of the Peripheral Nervous System

BACKGROUND AND OBJECTIVES

Chronic axonal polyneuropathy is a common disease of the peripheral nervous system with increasing prevalence with age. Typical neurologic signs are present in patients with polyneuropathy but may also occur in individuals without disease. Owing to limited knowledge on normal aging of the peripheral nervous system, it can be difficult to distinguish peripheral nerve dysfunction due to disease from variations in normal aging. Therefore, we described the changes in neurologic examination and nerve conduction studies that accompany aging in the general population.

METHODS

In this cross-sectional population-based study, we screened participants for chronic polyneuropathy in a controlled environment using standardized methods including a symptom questionnaire, neurologic examination, and nerve conduction studies (NCS). Inclusion criteria were 40 years or older and living in a suburb of Rotterdam, the Netherlands. Participants not diagnosed with chronic polyneuropathy, based on the discussion of findings in the screening by an expert team, were included to determine the effect of age (range 41-96 years) on features of neurologic examination and NCS using frequency calculations and quantile regression analysis.

RESULTS

In total, 4,179 participants (mean age 64.5 ± 12.7 years, 54.9% female) were included of whom 3,780 (90.5%) did not fulfil the criteria for polyneuropathy. In the population without polyneuropathy, the frequency of normal features at neurologic examination declined with age, most pronounced for vibration sense at the hallux (from 6.6 [SD ± 1.5] in 40-49 years to 3.6 [SD ± 3.1] in 80 years or older) and Achilles tendon reflexes (absent in 9% in 40-49 years up to 33% in 80 years or older). Superficial pain sensation and patellar tendon reflexes remained stable over time. Sural sensory nerve action potential (SNAP) amplitude declined with age from 11.2 μV in 40-49 years to 3.3 μV in 80 years or older. Nonrecordable SNAP amplitudes were found in 25.1% of the participants older than 80 years, more often in men (30.3%) than in women (21.0%).

DISCUSSION

This study showed the effect of age on features of neurologic examination and sural nerve amplitude in the general population. These findings are helpful to distinguish features suggesting polyneuropathy from variations of normal aging of the peripheral nervous system.

Sensory nerve conduction studies in probable painful neuropathy: comparing surface and near-nerve nerve conduction techniques

Introduction

We compared sensory nerve conduction studies (NCS) using surface and near-nerve recording electrodes in 53 patients with clinical probable painful neuropathy. Our aim was to validate the use of both recording techniques in that limited patient group.

Methods

Patients had sensory NCS using two established recording methods and quantitative sensory tests (QST). We compared normalised amplitudes of sensory sural nerve action potentials (SNAP) and sensory thresholds and used receiver operated curve (ROC) analysis of absolute SNAP amplitudes to find discriminatory levels predicting abnormal sensory thresholds.

Results

Mean sural SNAP z-scores differed depending on recording techniques (surface −1.0: SD 1.9; near-nerve −2.5: SD 1.7) with a numeric mean difference of −1.49 (Bland-Altman test: CI −1.872 to −1.12) with surface technique giving the z-value closest to zero. We documented a significant bias between the methods. Fifteen patients (28.3%) and 30 (56.6%) patients had abnormal results, respectively (χ2 test: p<0.001).

Sural SNAP amplitudes correlated significantly with vibration thresholds using the near-nerve (p<0.02) but not using the surface technique (p=0.11).

ROC analysis gave an optimal discriminative value of SNAP amplitudes for each QST measure, which were similar to our lower limit of normal values from investigating normal controls using near-nerve but not surface recording.

Conclusion

In patients with probable painful neuropathy, choosing sensory NCS technique introduces a bias in the diagnostic outcome. Differences in test performance suggest that using a normal sural NCS alone to delineate small fibre neuropathy from mixed neuropathy could result in poorly defined diagnostic groups.

Clinical polyneuropathy does not increase with prediabetes or metabolic syndrome in the Japanese general population

AIMS/INTRODUCTION

The prevalence of clinical polyneuropathies (ClinPNs) or nerve conduction abnormality (NCA) in the groups stratified by glucose tolerance, individual components of metabolic syndrome (metabolic syndrome [MetS] components: hypertension, dyslipidemia, obesity) and MetS defined by the International Diabetes Federation consensus was investigated in the Japanese general population. Factors associated with ClinPN and NCA were also identified.

MATERIALS AND METHODS

A total of 625 examinees of regional medical checkup programs were recruited to this cross-sectional study. ClinPNs were diagnosed by the Toronto Consensus. NCA was judged by at least one bilateral abnormality of sural nerve action potential amplitude or conduction velocity measured by a point-of-care nerve conduction device (DPNCheck). Clinical factors associated with ClinPNs or NCA were examined by multiple logistic regression analysis. Deteriorating factors of sural nerve action potential amplitude or conduction velocity values were also investigated in participants without diabetes (n = 550).

RESULTS

As for glucose tolerance, ClinPNs or NCA significantly increased only in known diabetes patients compared with other groups. There was no difference between prediabetes and the normal group. The prevalence of ClinPNs and NCA was not significantly related to MetS or MetS' components, except for frequent NCA in obesity. The factors significantly associated with both NCA and ClinPNs were smoking and known diabetes. In non-diabetic participants, aging, tall height and hypertension were significant deteriorating factors of nerve conduction functions.

CONCLUSIONS

In Japan, ClinPNs and NCA were increased in known diabetes patients, but did not increase in participants with prediabetes, MetS and MetS' components. Smoking and known diabetes were factors significantly associated with ClinPNs or NCA. Hypertension might be a modifiable deteriorating factor of nerve function.

Difference in normal limit values of nerve conduction parameters between Westerners and Japanese people might need to be considered when diagnosing diabetic polyneuropathy using a Point-of-Care Sural Nerve Conduction Device (NC-stat®/DPNCheck™)

AIM/INTRODUCTION

Studies on a novel point-of-care device for nerve conduction study called DPNCheck have been limited to Westerners. We aimed to clarify Japanese normal limits of nerve action potential amplitude (Amp) and conduction velocity by DPNCheck (investigation I), and the validity of DPNCheck to identify diabetic symmetric sensorimotor polyneuropathy (DSPN; investigation II).

MATERIALS AND METHODS

For investigation I, 463 non-neuropathic Japanese participants underwent DPNCheck examinations. Regression formulas calculating the normal limits of Amp and conduction velocity (Japanese regression formulas [JRF]) were determined by quantile regression and then compared with regression formulas of individuals from the USA (USRF). For investigation II, in 92 Japanese diabetes patients, 'probable DSPN' was diagnosed and nerve conduction abnormalities (NCA1: one or more abnormalities, and NCA2: two abnormalities in Amp and conduction velocity) were determined. Validity of NCAs to identify 'probable DSPN' was evaluated by determining sensitivity, specificity, reproducibility (kappa-coefficient) and the area under the curve of receiver operating characteristic curves.

RESULTS

For investigation I, JRF was different from USRF, and normal limits by JRF were higher than that of USRF. The prevalence of Amp abnormality calculated by JRF was significantly higher than that of USRF. For investigation II, the sensitivity, specificity and reproducibility of NCA1 and NCA2 judged from JRF were 85%, 86% and 0.57, and 43%, 100% and 0.56, respectively. These values of JRF were higher than those of USRF. The area under the curve of JRF (0.89) was larger than USRF (0.82).

CONCLUSIONS

A significant difference in the normal limits of nerve conduction parameters by DPNCheck between Japanese and USA individuals was suggested. Validity to identify DSPN of NCAs might improve by changing the judgment criteria from USRF to JRF.

High body mass and kidney dysfunction relate to worse nerve function, even in adults without neuropathy

Polyneuropathy is a prevalent and disabling disorder. Despite extensive evaluation, the cause often remains unknown. Factors that predispose for the development of polyneuropathy need to be identified. We investigated the effect of anthropometric and metabolic factors on peripheral nerve function in 908 participants of the population-based Rotterdam Study without any symptoms or signs of polyneuropathy. Participants underwent nerve conduction studies of the sural and peroneal nerve. Data on age, height, weight, waist circumference, diabetes, lipid levels, hypertension, and kidney function were collected. Regression analyses were used to investigate determinants of nerve action potential amplitudes. The frequency of abnormal sural sensory nerve action potential (SNAP) amplitudes increased with age from 1% under 60 years to 23% over 80 years. Similarly, the frequency of abnormal peroneal nerve compound motor action potential (CMAP) amplitudes increased from 4% to 13%. High weight and body mass index were independently associated with reduced sural SNAP amplitudes and peroneal CMAP amplitudes. Participants with hypertension and kidney dysfunction were more likely to have abnormal sural SNAP amplitudes. Older age, high weight, hypertension, and moderate kidney dysfunction might thus lead to peripheral nerve dysfunction in persons yet without symptoms or signs of polyneuropathy.

Sural and Radial Sensory Responses in Patients with Sensory Polyneuropathy

INTRODUCTION

The sural/radial nerve amplitude ratio (SRAR) is the quotient of the sensory nerve action potential (SNAP) amplitudes (Amp) of the sural and the superficial radial nerve. It has been hypothesized that this ratio can be used for the detection of early axonal loss, because the sural SNAP amplitude will decrease first, thereby also decreasing the SRAR value.

OBJECTIVES

To determine the sensitivity and specificity of SRAR, age-adjusted sural and radial SNAP Amp in the diagnosis of axonal sensory polyneuropathy in cancer patients.

DESIGN

Retrospective review.

SETTING

Comprehensive cancer center.

PATIENTS

One hundred and ninety one EMG reports from January 2001 to December 2005.

METHODS

The independent variable is the diagnosis of axonal sensory polyneuropathy in the EMG reports that is based on multiple tests.

MAIN OUTCOME MEASUREMENTS

We assessed the agreement between classifications of axonal sensory polyneuropathy made using the current 'gold standard' and the proposed method that is based on patients' age-adjusted radial and sural SNAP amplitude; an SRAR being above or below the normal value (0.21).

RESULTS

We found that the sensitivities for age-adjusted radial SNAP Amp, age-adjusted sural SNAP Amp, and SRAR were 33%, 64%, 56% respectively; the specificities were 85%, 70%, 77% respectively.

CONCLUSIONS

SRAR is neither the most sensitive, nor the most specific in the diagnosis of axonal sensory polyneuropathy.

Effects of anthropometric factors on nerve conduction: an electrophysiologic study of feet

BACKGROUND

Previous studies have shown that age, sex, and body mass index (BMI) affect the amplitude of sensory nerve action potentials (SNAPs), but the total effects of multiple factors and the most prominently affected nerves have not been elucidated. We systematically investigated the effects of these factors on motor and sensory nerves of the feet.

METHODS

The amplitude, latency, and conduction velocity of compound muscle action potential (CMAP), SNAP, and mixed nerve action potential (MNAP) of the posterior tibial, calcaneal, distal posterior tibial, medial and lateral plantar, and sural nerves were measured in 30 healthy individuals (60 feet). The effects of age, sex, height, and BMI on each nerve were estimated by correlation and linear regression analyses.

RESULTS

The amplitude of posterior tibial CMAP and distal posterior tibial MNAP decreased with BMI. The amplitude of medial plantar MNAP and sural SNAP decreased with height. The conduction velocity of calcaneal SNAP and distal posterior tibial and lateral plantar MNAP decreased with height and BMI. The conduction velocity of medial plantar MNAP decreased only with height. The latency of posterior tibial CMAP increased with age and height. The latency of lateral plantar CMAP and calcaneal SNAP increased with height. The latency of lateral plantar MNAP increased with BMI.

CONCLUSIONS

The effects of age, sex, height, and BMI in foot nerve conduction studies are not identical. Height and BMI were shown to strongly affect motor, sensory, and mixed nerve conduction. Further investigations are needed.

Relationship of estimated dietary intake of n-3 polyunsaturated fatty acids from fish with peripheral nerve function after adjusting for mercury exposure

BACKGROUND

Some clinical studies have suggested that ingestion of n-3 polyunsaturated fatty acids (PUFA) has neuroprotective effects on peripheral nerve function. However, few epidemiological studies have examined the effect of dietary n-3 PUFA intake from fish consumption on peripheral nerve function, and none have controlled for co-occurrence of methylmercury exposure from fish consumption.

OBJECTIVES

We evaluated the effect of estimated dietary n-3 PUFA intake on peripheral nerve function after adjusting for biomarkers of methylmercury and elemental mercury in a convenience sample of 515 dental professionals.

METHODS

We measured sensory nerve conduction (peak latency and amplitude) of the median, ulnar and sural nerves and total mercury concentrations in hair and urine samples. We estimated daily intake (mg/day) of the total n-3 PUFA, n-3 docosahexaenoic acid (DHA), and n-3 eicosapentaenoic acid (EPA) based on a self-administrated fish consumption frequency questionnaire. We also collected information on mercury exposure, demographics and other covariates.

RESULTS

The estimated median intakes of total n-3 PUFA, n-3 EPA, and n-3 DHA were 447, 105, and 179 mg/day, respectively. The mean mercury concentrations in urine (1.05 μg/L) and hair (0.49 μg/g) were not significantly different from the US general population. We found no consistent association between n-3 PUFA intake and sensory nerve conduction after adjusting for mercury concentrations in hair and urine although some positive associations were observed with the sural nerve.

CONCLUSIONS

In a convenience sample of dental professionals, we found little evidence suggesting that dietary intake of n-3 PUFAs from fish has any impact on peripheral nerve function after adjustment for methylmercury exposure from fish and elemental mercury exposure from dental amalgam.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

An investigation of modifying effects of single nucleotide polymorphisms in metabolism-related genes on the relationship between peripheral nerve function and mercury levels in urine and hair

Mercury (Hg) is a potent neurotoxicant. We hypothesized that single nucleotide polymorphisms (SNPs) in genes coding glutathione-related proteins, selenoproteins and metallothioneins may modify the relationship of mercury biomarkers with changes in peripheral nerve function. Dental professionals (n=515) were recruited in 2009 and 2010. Sensory nerve function (onset latency, peak latency and amplitude) of the median, ulnar and sural nerves was recorded. Samples of urine, hair and DNA were collected. Covariates related to demographics, nerve function and elemental and methyl-mercury exposure were also collected. Subjects included 244 dentists (47.4%) and 269 non-dentists (52.2%; mostly dental hygienists and dental assistants). The mean mercury levels in urine (1.06 μg/L) and hair (0.51 μg/g) were not significantly different from the US general population (0.95 μg/L and 0.47 μg/g, respectively). In multivariate linear models predicting nerve function adjusting for covariates, only 3 out of a total of 504 models showed stable and statistically significant interaction of SNPs with mercury biomarkers. Overall, given the possibility of false positives, the results suggested little evidence of effect modification of the SNPs on the relationship between mercury biomarkers with peripheral nerve function at exposure levels that are relevant to the general US population.

Differential aging of median and ulnar sensory nerve parameters

INTRODUCTION

Nerve conduction velocity slows and amplitude declines with aging.

METHODS

Median and ulnar sensory nerves were tested at the annual meetings of the American Dental Association. Seven hundred four subjects had at least two observations. The rate of change in the nerve parameters was estimated while controlling for gender, age, change in hand temperature, baseline body mass index (BMI), and change in BMI.

RESULTS

Amplitudes of the median sensory nerve action potentials decreased by 0.58 μV per year, whereas conduction velocity decreased at a rate of 0.41 m/s per year. Corresponding values for the ulnar nerve were 0.89 μV and 0.29 m/s per year. The rates of change in amplitudes did not differ, but the median nerve demonstrated a more rapid loss of conduction velocity.

CONCLUSIONS

The rate of change for the median conduction velocity was higher than previously reported. The rate of change of median conduction velocity was significantly greater than for the ulnar nerve.

Nerve conduction study of the superficial peroneal sensory distal branches in koreans

Objective

To perform nerve conduction studies of the four branches of the superficial peroneal nerves to determine normal values and anatomic variations in Koreans.

Method

Antidromic sensory nerve conduction studies of the four distal branches were performed on 70 healthy subjects (100 feet). We applied electrical stimulation at the midpoint of medial and lateral malleoli for the medial dorsal cutaneous nerve (MDCN), and at the lateral 1/4 point between the medial and lateral malleoli for the 2 branches of the intermediate dorsal cutaneous nerve (IDCN).

Results

Reference values (mean±SD) of the onset/ peak latency (ms)/ sensory action potential amplitude (µV) for the two branches of the MDCN and for the first branch of the IDCN were 2.2±0.3/2.9±0.3/9.2±3.1, 2.2±0.3/2.8±0.3/9.1±3.0 and 2.3±0.4/2.9±0.3/8.5±2.8, respectively. For the second IDCN branch, the reference values were 2.3±0.4/3.0±0.4/7.1±2.6 but anomalous sural innervation was also found. Three types of IDCN innervations to the fourth interdigital web space were detected. In type I, the fourth interdigital webspace was innervated solely by the IDCN, whereas in type II, it was innervated by both the IDCN and distal sural nerve. In type III, it was solely innervated by the distal sural nerve.

Conclusion

The results of this study show the reference values of the distal sensory branches of the superficial peroneal nerve, and provide information on the variant innervations to the fourth interdigital web space.

The effect of obesity on the assessment of diabetic peripheral neuropathy: a comparison of Michigan patient version test and Michigan physical assessment

OBJECTIVE

Nerve conduction studies (NCS) and Michigan Neuropathy Screening Instrument (MNSI) are commonly used to make the diagnosis of diabetic peripheral neuropathy. The objective of this study was to compare the diagnostic values of MNSI patient version test and physical test for the assessment of the diabetic peripheral neuropathy in obese vs. non-obese patients.

METHOD

This study was conducted on 70 type 2 diabetic patients. We carried out the MNSI patient version test and MNSI physical assessment test. Nerve conduction studies were performed for the diagnosis of the diabetic peripheral neuropathy.

RESULTS

In diabetic peripheral neuropathy (DPN) determined by NCS, the independent prediction of peripheral neuropathy was the score of Michigan physical assessment (odds 2.0; CI: 1.3-3.0). In BMI (body mass index) ≥ 30 diabetic patients who have peripheral neuropathy, Michigan patient version test is not significant. But the score of Michigan physical assessment is significantly increased in these patients compared to patients without peripheral neuropathy. In BMI<30 diabetic patients who have peripheral neuropathy, scores of both Michigan patient version and physical assessment instruments are significantly increased.

CONCLUSION

To screen diabetic peripheral neuropathy, Michigan physical assessment may be more useful instrument than Michigan patient version test in obese diabetic patients.

Determinants of epidermal nerve fiber density in normal individuals

We studied the relationship between epidermal innervation and age, gender, height, and weight. Intraepidermal nerve fiber density (IENFD) of skin biopsies obtained from the proximal thigh and ankle of 84 normal individuals was quantified. A linear regression model was performed using IENFD at the thigh, IENFD at the ankle, and the thigh IENFD/ankle IENFD ratio, with age, gender, and height-weight interaction as predictors. An independent, negative correlation was found between age and IENFD at the ankle. No correlation was found between age and IENFD at the thigh. With increasing age the thigh IENFD/ankle IENFD ratio, a measure of the length-dependent distal-to-proximal gradient of epidermal nerve density, increased significantly. Gender, height, and body weight did not independently influence IENFD at either site. In normal individuals, distal epidermal innervation decreases in a length-dependent manner with advancing age. This must be considered when interpreting IENFD in disease states.

The relative contributions of the medial sural and peroneal communicating nerves to the sural nerve

The medial sural cutaneous nerve (MSCN) and peroneal communicating nerve (PCN) conjoin in the calf area to form the sural nerve (SN). In previous anatomic studies, there was unresolved debate as to the main contributor to the sural nerve, and the relative contributions of MSCN and PCN had not been studied. The purpose of this study is to determine their relative neurophysiologic contributions to the SN by nerve conduction study (NCS). A total of 47 healthy subjects (25 males and 22 females, mean age 29.6 +/- 10.4 yrs, range 20-59 yrs) participated in the study. This study employed the orthodromic nerve conduction technique: stimulation at the ankle and recording at the mid calf (SN); specifically, we preformed stimulation at the mid calf (MSCN, PCN) and recording at 14 cm proximal to the middle of the popliteal fossa (MSCN) and fibular head (PCN). The onset and peak latencies (ms) were SN 2.3 +/- 0.2 and 3.0 +/- 0.2; MSCN 2.1 +/- 0.2 and 2.8 +/- 0.2; and PCN 2.1 +/- 0.2 and 2.8 +/- 0.2. The peak-to-peak amplitudes (microV) and areas (nVsec) of the SN, MSCN, and PCN were 9.7 +/- 3.9, 7.0 +/- 4.7, and 5.0 +/- 3.2; and 7.2 +/- 2.9, 5.7 +/- 3.4, and 4.0 +/- 2.4, respectively. The side-to-side difference was not statistically significant. The main contributor to the SN was found to be the MSCN. The relative contribution ratio of the MSCN to the PCN was 1.37:1 by amplitude and 1.42:1 by area. However, in 32.9% of the subjects, the contribution of the PCN was greater than that of the MSCN.

Validation of Michigan neuropathy screening instrument for diabetic peripheral neuropathy

OBJECTIVE

The reliability and accuracy of the Michigan neuropathy screening instrument (MNSI) have been discussed recently. As a result of the difficulties of performing and analyzing nerve biopsy as a standard diagnostic test, electromyography and neuronography is used as the best alternative diagnostic procedure. The objective of this study was to determine the diagnostic performance of the test characteristics and cut-off point of MNSI scoring for the diagnosis of diabetic peripheral neuropathy.

METHOD

Over a 2-year period, a cross-sectional study was conducted on 176 type 2 diabetic patients. An internist carried out the MNSI and the sum of scores varying from 0 to 1 for each abnormality as revealed in foot appearance, ulceration, ankle reflexes and vibratory perception has been recorded. A neurologist, who was blind to the MNSI scores, performed all neurophysiological studies. The test performance characteristics of the MNSI procedure were measured for different cut-off values.

RESULTS

MNSI scores of 1.5, 2.0, 2.5 and 3.0 were assessed as cut-off values. Sensitivities were 79%, 65%, 50% and 35% and specificities were 65%, 83%, 91% and 94%, respectively. Positive predictive values increased and negative predictive values decreased for each score. Accuracies, likelihood ratios and post-test probabilities were measured.

CONCLUSION

The accuracy of MNSI scoring makes it a useful screening test for diabetic neuropathy in taking a decision regarding which patients should be referred to a neurologist for electrophysiological studies. High specificity, likelihood ratios over 5 and a moderate to good post-test probability give a high diagnostic impact for MNSI scoring. We suggest a cut-off point of 2 for the MNSI procedure. However, electrophysiological studies should be considered when the patient has signs and symptoms other than those rated by the MNSI, suggesting peripheral nerve involvement, and also because the MNSI is still just a screening test.

Measurement of skin vasoconstrictor response in healthy subjects

OBJECTIVES

Laser Doppler flowmetry enables non-invasive quantification of skin blood flow and its sympathetically mediated change. Four different maneuvers were performed in 60 healthy subjects aged 20-78 years to investigate their variability, reproducibility and to determine the influence of gender, age and height.

MATERIAL AND METHODS

Skin blood flow was measured on the pulp of both index fingers using laser Doppler flowmetry. Vasoconstriction was induced by deep inspiratory gasp, arm dependency, acoustic stimulation and a modified cold pressor test.

RESULTS

More than 95% of normal subjects showed a vasoconstrictor response to cold pressure test and 100% to inspiratory gasp. In all other maneuvers vasoconstrictor response was less reliable. The magnitude of vasoconstrictor responses decreased with age in all maneuvers, while latencies remained unchanged. Only during inspiratory gasp men showed more pronounced vasoconstrictor response compared with women. Body height influenced latencies if peripheral stimuli were applied like in the cold pressor and arm dependency tests.

CONCLUSIONS

Inspiratory gasp and the modified cold pressor test were found to be more suitable maneuvers for routine clinical testing than arm dependency and acoustic stimulation. Normal data also for side differences are provided as a base for routine clinical testing in systemic and unilateral neurological disorders.

Sural and radial sensory responses in healthy adults: diagnostic implications for polyneuropathy

We prospectively performed sural and radial sensory nerve conduction studies in 92 healthy subjects, aged between 21 and 88 years, both to determine the lower limits of normal (LLN) and to assess the effects of age and body mass index (BMI) on the sural and radial sensory nerve action potential (SNAP) amplitudes and on the sural/radial amplitude ratio (SRAR). Using the nonparametric bootstrap method to calculate 95% confidence intervals, we found that the 5% LLN values for sural and radial SNAPs were 14 microV and 25.5 microV in subjects aged < or =39 years, 7 microV and 17.4 microV in subjects aged 40-59 years, and 3 microV and 12 microV in subjects aged > or =60 years. The 5% LLN for SRAR for all patients was 0.21. Sural and radial SNAP amplitudes but not SRAR were strongly and inversely correlated with age and BMI. These age-adjusted normal values and revised SRAR will aid in the electrodiagnosis of polyneuropathy.

Effect of aging on sensory nerve conduction study parameters

Research evaluating the changes in nerve conduction with time has been limited to cross-sectional studies. We present a cohort study estimating how sensory nerve conduction study (NCS) parameters change with time when subjects are measured at two time-points. We evaluated 440 working adults by performing median and ulnar antidromic sensory NCS of both hands on two occasions, about 5.4 years (range, 4.3-7.0 years) apart. The rate of change in the NCS parameters was estimated using a mixed-models analysis controlling for each hand, gender, age, and body mass index (BMI). After controlling for gender, age, height, and BMI, the amplitudes of the median sensory nerve action potentials (SNAP) decreased by about 2.3 microV, peak latencies increased by 0.11 ms, onset latencies increased by 0.07 ms, and conduction velocities decreased by 1.1 m/s over 5 years. Corresponding values for the ulnar nerve were 1.75 microV, 0.06 ms, 0.04 ms, and 0.71 m/s, respectively. The findings are consistent with the findings of previous cross-sectional studies. The rate of change over time was not affected by hand (dominant versus nondominant hand), gender, age, or BMI at baseline. The rate of change seen with some of the median nerve parameters was significantly greater than that with the ulnar nerve.

Dorsal ulnar cutaneous nerve conduction: reference values

We investigated the reference values of the dorsal ulnar cutaneous nerve (DUC) sensory nerve conduction (SNC) in 66 healthy individuals. Measurements were processed using stimulating electrodes positioned between the ulnar bone and the flexor carpi ulnaris muscle, 11-13 cm proximal to the active electrode recording. Superficial recording electrodes were placed on the fourth intermetacarpal space. The mean sensory conduction velocity (SCV) in males was 63.7 - 0.16 x age +/- 3.36 m/s and in females was 57.7 +/- 3.37 m/s. The mean sensory nerve action potential (SNAP) amplitude in males was 19.5 +/- 10.7 microV and in females was 24.6 +/- 5.8 microV. The mean SNAP duration was 0.96 +/- 0.13 ms. No significant differences regarding the DUC-SCV, distal latency, and SNAP duration or amplitude were found between both sides of the same subject. The amplitude of the SNAP was higher in females than males. The effects of age on DUC-SCV were distinct for each gender.

Influence of age and height on nerve conduction

Previous studies demonstrated age- and height-related slowing of nerve conduction velocity (NCV) and reduction in nerve response amplitude. Unfortunately, many studies examined discontinuous populations, preventing regression analysis. The correlation coefficients of available studies vary widely, preventing clear conclusions. We retrospectively examined 3969 clinically normal subjects ranging in age from 20 to 95 years from a total of 22,420 electrodiagnostic studies done between 1986 and 1998. The correlation of NCV with height was stronger than with age. Regression equations using both factors account for 12--27% of the variance. Responses were seen in the majority of patients aged 70 years and older, but the percentage of normals who had no response increased with advancing age. Age was strongly inversely correlated with the amplitudes of both sensory and motor responses, accounting for 7--16% of the variance. Regression equations using both height and age improved this correlation, accounting for 7--22% of the variance. Therefore, both height and age must be taken into consideration when normal values are developed.

Sural/radial amplitude ratio in the diagnosis of mild axonal polyneuropathy

As proximal nerves are relatively spared in length-dependent, axonal polyneuropathy, we theorized that a sural/radial amplitude ratio (SRAR) might be a sensitive indicator of mild polyneuropathy. In this study, sural amplitudes and SRARs in patients with signs of mild axonal polyneuropathy were compared to those of normal, age-matched control subjects. Sural and radial sensory responses were measured in a standard fashion in all subjects. Thirty polyneuropathy patients had an average SRAR of 0.29 as compared to 0.71 for the 30 normal subjects. An SRAR of less than 0.40 was a strong predictor of axonal polyneuropathy, with 90% sensitivity and 90% specificity, as compared to an absolute sural amplitude of less than 6.0 microV, which had sensitivity of only 66%. Additionally, unlike the sural amplitude, the ratio did not vary significantly with age. We conclude that the SRAR is a sensitive, specific, age-independent electrodiagnostic test for mild axonal polyneuropathy.

Analysis of 100 cases of free-muscle transplantation for facial paralysis

Free-muscle transplantation is the treatment of choice for long-standing facial paralysis. It enables the reconstructive surgeon to restore facial movement and some emotional animation. Despite all technical innovations and 20 years of experience with free-muscle transplantation, the aesthetic and functional outcomes of the surgery are still unpredictable. The present report reviews 100 free-muscle transplantations to the face by a single surgeon and analyzes various preoperative, intraoperative, and postoperative factors in relation to the functional recovery of the muscle transplants. These factors were demographic variables such as age, gender, and etiology as well as intraoperative variables such as choice of muscles, number of nerve coaptations, and ischemia time of the muscle. Additionally, four independent raters not involved in the care of these patients rated standardized preoperative and postoperative videos and judged the functional and aesthetic outcomes. From 1981 to 1993, 93 patients with facial paralysis underwent free-muscle transplantation. A total of 100 muscles were transplanted, since 7 patients received two muscle transplants. There were 33 male and 60 female patients ranging in age from 3 to 57 years, with an average of 22.2 +/- 14.9 years. The gracilis muscle was used in 63 cases of free-muscle transplantation, while the pectoralis minor was used in 34 cases. In 2 patients a segment of the rectus abdominis was transferred, and in 1 patient a small segment of the latissimus dorsi was transferred. In 89 patients the onset of muscle function was reported. The range was from 6 to 48 weeks postoperatively. The average was 21.6 +/- 9.14 weeks after muscle transplantation. The correlations showed a trend to earlier onset of function and higher aesthetic rating in young female patients. The intraoperative ischemia of the free muscle did not correlate with the onset of muscle function. Using a five-step scale of judgments, a higher postoperative rating was seen in 94 percent of the patients, and 80 percent of all patients achieved a moderate or better result.

Nerve, muscle, and neuromuscular junction electrophysiology at high temperature

Although the effect of low temperature on the peripheral nervous system has been systematically studied, the effect of high temperature has not. We investigated the effect of elevating limb temperature from 32 degrees C to 42 degrees C by performing sequential motor studies, antidromic sensory studies, and 3-Hz repetitive stimulation in normal subjects. In addition, we recorded single motor units by using threshold stimulation. On average, motor amplitude and duration decreased by 27% and 19%, respectively, whereas sensory amplitude and duration decreased by 50% and 26%, respectively. Neuromuscular transmission remained normal at 42 degrees C. Single motor unit recordings revealed a reduction in amplitude of 26%, similar to the overall reduction in compound motor amplitude. These findings demonstrate that significant reductions in sensory and motor amplitudes can occur in normal nerves at high temperature; we hypothesize that these changes are secondary to alterations in nerve and muscle ion channel function.

Electrophysiological findings in a Danish family with Machado-Joseph disease

Machado-Joseph disease (MJD) is a neurodegenerative disorder with autosomal dominant inheritance, We have carried out electrophysiological studies in 8 individuals belonging to a Danish family with several affected members. Five had an expanded trinucleotide (CAG) repeat sequence in the MJD1 gene on chromosome 14 indicating MJD, while 3 unaffected individuals had normal repeat lengths. Three individuals with repeat expansion had clinical symptoms and signs of the Machado or "type III" phenotype, whereas 2 had slight symptoms and signs only, Electrophysiological evaluation included visual, somatosensory, and auditory brain stem evoked potentials, quantitative electromyography, and nerve conduction studies. In the patients with clinical MJD, evoked potential studies showed multimodal abnormalities, electromyography showed neurogenic changes, and nerve conduction studies showed signs of severe loss of motor and sensory nerve fibers. Of the 2 patients with slight symptoms and signs, 1 had evidence of peripheral and central affection, while the other had slight signs of a central affection. This study provides insight into the distribution and character of electrophysiological abnormalities in MJD of putative importance for an understanding of the pathogenesis of the disease, and for monitoring disease progress, or the outcome of a possible treatment.

Normal values of nerve conduction in children and adolescents

Healthy children and adolescents (n = 128) ranging in age from 6 to 20 years and in height from 114 to 193 cm underwent studies of median, peroneal and sural nerves bilaterally, including nerve conduction velocity, amplitude and motor distal latencies. Arms and legs were heated in all subjects to obtain skin temperatures around 34 degrees C. Both motor and sensory nerve conduction velocities were found to correlate more with height than with age. There was a strong negative correlation between height and peroneal conduction velocity (r = -0.40, P < 0.0001). On the contrary, a positive correlation was found between height and both median sensory (r = 0.30, P < 0.0001) and motor (r = 0.22, P < 0.001) conduction velocities. Skin temperature, even near 34 degrees C, had a strong effect on conduction velocity and motor distal latencies. It is concluded that consideration of height and temperature will improve the diagnostic safety of nerve conduction measurements in children and young adults.

Compound sensory action potentials evoked by tactile and by electrical stimulation in normal median and sural nerves

The compound sensory action potential evoked by electrical stimulation provides a measure of the number and physiological properties of myelinated fibers in the nerve but does not allow evaluation of the most distal part of the sensory nerve. This study compares the compound sensory action potential, evoked by electrical and tactile stimuli, and recorded through needle electrodes placed close to the median and sural nerves of 22 normal males aged 16-51 years. The tactile probe, with a slight preindentation, delivered an indentation of the skin of 200 microns at a rate of 400 microns/ms at the tip of digit III and the dorsolateral side of the foot. The responses were recorded from the median nerve at wrist and elbow and from the sural nerve at the lateral malleolus and midcalf. The amplitudes of the responses averaged 0.5 microV and 0.7 microV in the sural and the median nerves (P < 0.02), respectively, which was only 5-10% of the amplitude evoked by electrical stimulation. The mean maximal conduction velocity determined by tactile stimulation was 54 m/s in the sural nerve compared with 65 m/s in the median nerve and similar to that calculated after electrical stimulation. In the median nerve the sensory conduction velocity was 8% faster than the motor conduction velocity. These findings indicated that only a fraction of the fibers in the nerve were activated by the probe and that the response was conducted along large myelinated sensory fibers. The latency of the tactile response was longer than that of the electrically evoked response due to the receptor delay and conduction along thin distal fiber portions. The delay at the mechanoreceptors was about 1 ms in the sural and 0.65 ms in the median nerve (P < 0.01).

Covariates of human peripheral nerve function: I. Nerve conduction velocity and amplitude

A systematic investigation of covariates of nerve conduction measures was performed on data collected by the U.S. Centers for Disease Control. Nerve conduction velocity and amplitude were obtained for the median motor, median sensory, ulnar sensory, peroneal motor, and sural sensory nerves on 4,462 subjects. The magnitude of effect of skin temperature, height, body mass index, age, race, place of military service, smoking status, alcohol consumption, income, and EMG examiner was estimated for all 10 conduction outcomes. The major covariates were skin temperature, height, and examiner. Covariates with smaller but not unimportant effects on conduction outcomes were age, race, smoking status, and income. Alcohol consumption was associated with only small effects on conduction measures. These results provide an empirical basis for selection of variables to control in studies employing nerve conduction measures.

Comparison of two techniques to measure the motor nerve conduction velocity distribution

Hopf's technique to measure the distribution of motor nerve conduction velocities (DMCV) has been compared with the technique introduced by Ingram et al. in the peroneal nerve of 28 healthy subjects 41.2 (S.D. 8.4) years. Twenty subjects were examined twice. Both techniques yielded an equal DMCV and equally reproducible results. Group mean velocities for the slowest examined (MNCV95) motor nerve fibres were 39.0 m/sec (S.D. 3.3) for Ingram's technique and 38.6 (S.D. 3.6) for Hopf's technique. The conventional MNCV was always slower than the velocity of the 5% fastest fibres estimated from the DMCV. Ingram's technique may have a number of merits which may have been obscured by measurement in the peroneal nerve, which may be of advantage in shorter nerve segments or faster nerve fibres. On the basis of our data in the peroneal nerve of healthy subjects no preference can be given for either of the techniques.

Assessment of diabetic neuropathy: definition of norm and discrimination of abnormal nerve function

One hundred one normal subjects and 46 patients were investigated. Various objective and subjective tests for polyneuropathies were compared. Motor and sensory nerve conduction velocities are the most sensitive tests. In normals, age hardly influenced nerve conduction velocities. This is believed to be a result of the strict exclusion criteria. Diagnostic sensitivity is also high with the vibration fork test and with vibratometry at the big toe. Results with the method of limits are as reliable and sensitive as more cumbersome techniques, such as the titration method and the forced choice method. Thermal thresholds and cardiovascular tests are less sensitive. The most correct overall classification is attained with a combination of tests reflecting the function of different nerve fiber classes in the peripheral and autonomic nervous systems.