Objective: The importance of normative peripheral nerve data is increasing due to the advances in medical implantation, microsurgical suturing, and tubulization repair techniques. Because the median and ulnar nerves are often affected, their normal values must be reliable. The objective of this study was to create a larger database of normative values for the first and second lumbrical responses. The differences between the second lumbrical response and the interosseous response were also studied.
Background: The available literature is lacking in sample size and rigor, preventing reliable interpretations of normal values.
Methods: One hundred ninety-six asymptomatic subjects without risk factors for neuropathy were recruited and tested. Stimulations were performed with recording at the first lumbrical, second lumbrical, and interosseous muscles.
Results: Mean latency to the first lumbrical was 3.6 +/- 0.4 ms. Mean amplitude was 2.5 +/- 2.0 mV. The mean difference between latencies to the first lumbrical and second lumbrical was 0.1 +/- 0.3 ms, with the second lumbrical usually being the larger value. The mean difference between latencies to the abductor pollicic brevis (APB) and the first lumbrical was 0.2 +/- 0.4 ms, with the APB latency usually being the larger value. Mean latency to the second lumbrical was 3.7 +/- 0.4 ms and to the interosseous was 3.1 +/- 0.3 ms. Mean amplitude to the second lumbrical was 3.0 +/- 2.0 mV and to the interosseous was 6.9 +/- 2.3 mV. The mean difference between latencies to the second lumbrical and interosseous was 0.4 +/- 0.4 ms, with the second lumbrical usually being the larger value. The upper limit of normal increase of latency of the second lumbrical over the interosseous was 1.2 ms. The upper limit of normal increase of latency in subjects for which the interosseous latency exceeded the second lumbrical was 0.2 ms.
Conclusions: This study provides a large normative database for nerve conduction studies to the first and second lumbricals, as well as to the second interosseous muscle.