Acceptable Differences in Sensory and Motor Latencies Between the Median and Ulnar Nerves

Abstract

The median and ulnar nerves are often studied during the same electrodiagnostic examination. The sensory and motor latencies of these nerves have been compared to detect a common electrodiagnostic entity: median neuropathy at the wrist. However, this comparison could also be used to diagnose less common ulnar pathology. For this reason, it is important to establish normal values for comparing median and ulnar sensory and motor latencies. Previous research deriving these differences in latency has had some limitations. The purpose of this study was to derive an improved normative database for the acceptable differences in latency between the median and ulnar sensory and motor nerves of the same limb. Median and ulnar sensory and motor latencies were obtained from 219 and 238 asymptomatic risk-factor-free subjects, respectively. An analysis of variance was performed to determine whether physical characteristics, specifically age, race, gender, height, or body mass index (as an indicator of obesity), correlated with differences in latency. Differences in sensory latencies were unaffected by physical characteristics. The upper limit of normal difference between median and ulnar (median longer than ulnar) onset latency was 0.5 ms (97th percentile), whereas the peak latency value was 0.4 ms (97th percentile). The upper limit of normal difference between ulnar-versus-median (ulnar longer than median) onset latency was 0.3 ms (97th percentile), whereas the peak-latency value was 0.5 ms (97th percentile). The mean difference in motor latencies correlated with age, with older subjects having a greater variability. In subjects aged 50 and over, the mean difference in median-versus-ulnar latency was 0.9 ms +/- 0.4 ms. The upper limit of normal difference (median longer than ulnar) was 1.7 ms (97th percentile). The upper limit of normal ulnar motor latency is attained if the ulnar latency comes within 0.3 ms of the median latency. In individuals less than 50 years of age, the mean difference in latency was 0.6 ms +/- 0.4 ms, with the median latency usually being greater than the ulnar. The upper limit of normal difference (median longer than ulnar) was 1.4 ms (97th percentile), whereas the upper limit of ulnar latency relative to median latency was attained if the ulnar latency was equal to median latency.

Electrodiagnostic reference data for sensory nerve conduction studies in Saudi Arabia

“…These tests, in addition to the lumbrical-interossei study (not assessed in the present study), are important for evaluating patients with carpal tunnel syndrome. Our findings are consistent with the median-ulnar digit SNAP comparison study reported by Grossart et al 26 and the median-ulnar mixed palmar PL difference reported by Buschbacher. 27 Another study reported a slightly larger median-ulnar D4 PL difference (0.5 ms) than the values in our study.…”

Electrodiagnostic reference values for upper and lower limb nerve conduction studies in adult populations

“…This means that the ulnar motor latency should not be longer than the median motor latency. If it is, then ulnar nerve pathology across the wrist may be present . Median and ulnar sensory nerve latency comparisons, in contrast to the motor nerve comparisons, did not show a substantial age influence.…”

“…Median and ulnar sensory nerve latency comparisons, in contrast to the motor nerve comparisons, did not show a substantial age influence. For the entire group, the median‐to‐ulnar peak latency comparison had an upper (97th percentile) limit of 0.4 ms, whereas the ulnar‐to‐median upper limit comparison was similar at 0.5 ms (Table ) …”

“…Comparisons of median and ulnar motor nerve conduction across the wrist, (intra‐hand comparisons) are helpful in minimizing the confounding effects of age, height, and limb temperature. A comparison of these latency comparisons provides reference values and utilizes the same methodology, sample, and non‐parametric statistics as in the main articles (Table ) . The distribution of median‐to‐ulnar motor latency comparisons differed from ulnar‐to‐median motor latency comparisons.…”

Work-Related Carpal Tunnel Syndrome

“…Less than 10% of patients with clinical CTS have normal NCV results. [26][27][28][29][30] In these cases, the treating physician should be sure that the most sensitive and specific NCV tests are done. If not, a request for these tests should be made.…”