Sural nerve conduction: Amplitude and distal latency of sensory nerve action potential

Background: The sensory nerve action potential (SNAP) is an important factor in the electro diagnostic evaluation of a patient with suspected peripheral neuropathy. Sural nerve is the most frequently studied nerve in the electrophysiology. For proper diagnosis sural sensory conduction abnormalities, a reference data are required for each electrophysiology laboratory. Aims and Objectives: The aim of the study was to find out normative reference data of amplitude and distal latency (DL) of sural SNAP for Northern Kerala population. Materials and Methods: The study was designed as cross-sectional and observational study and analysis of values was done using SPSS version 16. A total of 250 healthy subjects of age 15–50 from Northern Kerala participated in the study which included equal number of males and females. Results: Normative reference data for sensory amplitude and DL were derived in the present study. Sensory amplitude was more and DL was found to be less in female population, indicating faster nerve conduction in female. Conclusion: The reference data derived here can be utilized to detect any abnormality sural nerve sensory conduction. The gender effect on sural nerve sensory conduction parameters can be attributed to the height difference, as nerve conduction velocity is inversely proportional to height.

Nerve Conduction Studies in Asymptomatic HIV Positive Persons

Background: Nerve Conduction Studies were performed in asymptomatic HIV positive persons and corresponding controls to detect subclinical peripheral nervous system involvement in early stage of HIV. Aims & Objective: To perform Nerve Conduction Studies in asymptomatic HIV positive persons and corresponding controls. Material and Methods: In this study,100 participants in the age group 25-45 years were selected. In study group, 50 3 participants who were HIV positive and asymptomatic (CD4 count > 350 cells/mm ) and were not on Anti Retro Viral Treatment (ART), were included. In control group 50 healthy age matched HIV negative participants were included. We performed Nerve Conduction Studies in these participants. For motor nerves, Distal Latency (DL), Motor Nerve Conduction Velocity (MNCV), Compound Muscle Action Potential (CMAP) amplitude were measured and for sensory nerves Onset Latency (OL), Sensory Nerve Conduction Velocity (SNCV) and Sensory Nerve Action Potential (SNAP) amplitude were measured. Results: Nerve Conduction Studies in asymptomatic HIV revealed that, MNCV was significantly decreased for median motor nerve and tibial motor nerve in study group compared to control group, SNAP was significantly reduced for median sensory nerve in study group compared to control group, OL was significantly prolonged for sural nerve in study group than control group and SNCV was significantly decreased for sural nerve in study group than control group. Conclusion: Nerve Conduction Studies in asymptomatic HIV positive persons suggests subclinical peripheral nervous system involvement in early stages of HIV. Hence Nerve Conduction Studies can be important to detect subclinical peripheral nervous system involvement in the early stages of HIV.

Low amplitude dorsal ulnar cutaneous nerve sensory nerve action potential from cross over innervation. Can nerve ultrasound help?

The ulnar dorsal aspect of the hand is predominantly innervated by the dorsal ulnar cutaneous nerve with variable input from the superficial radial cutaneous nerve. This cross innervation can cause difficulty in interpreting low amplitude sensory nerve action potential for the dorsal ulnar cutaneous nerve particularly when facing suspected ulnar neuropathyat the elbow. In three subjects with low dorsal ulnar cutaneous sensory nerve action potential amplitude due to cross over with the superficial radial nerve, we compared amplitude with nerve circumference and fascicular count as measured by ultrasound. Dorsal ulnar cutaneous nerve circumference was significantly smaller where there was low sensory nerve action potential amplitude and showed fewer fascicles. Nerve ultrasonography may be a useful additional test modality to determine if low dorsal ulnar cutaneous nerve amplitude is physiological.

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.

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.

Comparison of Sensory Nerve Action Potential Parameters Using Different Recording Electrodes

OBJECTIVE: To investigate the influence of five different recording electrodes on the various parameters of sensory nerve action potentials (SNAPs). METHOD: Median sensory nerve conduction study was performed in 50 normal subjects using different five types of recording electrodes-disc electrode, ring electrode, bar electrode and two kinds of felt-tip bar electrodes (type 1 and 2). The interelectrode distances between active and reference electrodes were set at 4 cm for the disc and ring electrodes. The bar electrode, felt-tip electrodes type 1 and 2 were fixed at interelectrode distances of 3 cm, 3.7 cm and 2.3 cm, respectively. Onset and peak latency, onset to peak amplitude, peak to peak amplitude and duration of negative spike of SNAPs were measured. These parameters were compared using ANOVA test. RESULTS: Onset and peak latencies of SNAPs recorded from five different electrodes were not different (p>0.05). Onset to peak and peak to peak amplitudes of SNAPs recorded from felt-tip type 2 electrode were significantly reduced compared to other electrodes (p<0.05). Onset to peak amplitude of SNAPs was also reduced when the ring electrode was used (p<0.05). The negative spike durations of SNAPs recorded from felt-tip type 2 and bar electrodes were shorter than other electrodes recording (p<0.05). CONCLUSION: Onset and peak latencies of SNAPs were not affected by the types of electrodes used. Shortening of interelectrode distance may be a main cause of reduction of peak to peak amplitude and negative spike duration of SNAPs.

How to Deal with the Latency of Unobtainable Responses in the Statistical Analysis

OBJECTIVE: To evaluate the usability of near-nerve needle recording techniques in cases of unrecordable sensory nerve action potentials (SNAPs) with a surface electrode and to determine a proper alternative value of the missing latencies. METHOD: Twenty six hands of 23 patients with a carpal tunnel syndrome (CTS) and an unobtainable median SNAP by surface electrode were evaluated by the near-nerve needle recording of median SNAPs. Using the nerve conduction data of 113 patients with CTS, we have established 3 alternative values: maximal, 95 percentile and predictive latencies. The alternative values were compared with the mean onset latencies by the near-nerve needle recordings of median SNAPs. RESULTS: Median SNAPs were obtainable in the 22 out of 26 hands by the near-nerve recording technique. The mean onset latency was 5.51+/-0.36 ms. The alternative values from 113 patients with CTS were as follows: maximum latency, 6.9 ms; 95 percentile latency, 5.6 ms; and predictive latency, 5.52 ms (Y = 0.123x X 5.52491; Y, onset latency; X, amplitude; r2=0.564; p=0.00). The Predictive latency was nearest to the mean onset latency. CONCLUSION: To minimize the selection bias and statistical errors, the near nerve recording techniques proved to be a valuable method in cases of unrecordable SNAPs with surface electrode. For compensation of missing data, a proper alternative value can be obtained by the predictive latency calculated from a linear regression.