Roth technique--a new approach for measuring sensory neural conduction in the median and ulnar nerves: suggestion from the field.

Neural conduction studies (NCSs) are used to aid in the diagnosis of several neuromuscular disorders such as entrapment neuropathies, diffuse polyneuropathies, and other diseases of the peripheral nerves. Two methods used for the determination of sensory neural action potential (SNAP) amplitude and latency are the orthodromic (OD) and antidromic (AD) techniques. Median and ulnar sensory neural conduction of the upper extremity may be determined by stimulating the appropriate digital nerves and recording the SNAP from a more proximal site on the nerve (OD) or alternatively by stimulating the nerve proximally and recording the SNAP distally (AD). Sensory neural action potentials are routinely measured both orthodromically and antidromically in the upper extremities using either surface disk or ring electrodes over the digital nerve. Several studies have indicated that mean OD and AD neural conduction values are not significantly different. Buchthal and Rosenfalck in 1966 stated that no difference in mean latency values was found between the two methods. Other researchers have reported that sensory OD and AD latency values were essentially the same for healthy subjects. Melvin et al stated that AD latency was 0.2 msec slower than OD latency; however, this difference was not significant. Amplitudes for OD and AD SNAPs were not addressed in these earlier studies, with the exception of Kimura and Buchthal and colleagues who reported that AD amplitude of the digital SNAP appeared to be greater than OD amplitude when measured in the median nerve. The larger amplitude of the SNAP when measured antidromically is due to the proximity of the digital nerves to the skin (as opposed to the nerve trunk). In contrast to these studies, Chodoroff et al and Tashjian et al have found significant differences between OD versus AD latencies and amplitudes. Because of the discrepancy between reports concerning OD and AD sensory NCSs, a study is currently being performed at the Electrodiagnostic Laboratory, Neurology Service, Brooke Army Medical Center, D Greathouse, PhD, PT, is Director, US Army-Baylor University Graduate Program in Physical Therapy, US Army Academy of Health Sciences, and Associate Director, Electrodiagnostic Laboratory, Neurology Service, Brooke Army Medical Center, Fort Sam Houston, TX 78234 (USA).