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The objective of this study was to compare the sensitivity of needle electromyography of the abductor hallucis and peroneus tertius muscles in the diagnosis of mild length-dependent peripheral neuropathy (PN). Nerve conduction studies and needle examination were performed on 50 patients with clinical evidence of mild PN. Results demonstrated that the peroneus tertius is as sensitive and is more specific than the abductor hallucis. It is particularly useful when more proximal muscles, such as the tibialis anterior and medial gastrocnemius, are not yet involved.

In order to evaluate the clinical applicability of a neurophysiological technique, information is required about the effect of technical and subjective factors on the measured parameters, and whether these measures are reliable. The reliability of measurement of a given parameter is inversely related to the variability shown by a set of measurements of that parameter made on the same subject under similar conditions. Reliable measures are fundamental to the clinical utility of any technique. We evaluated the reliability using the intraclass correlation coefficient (ICC), and assessed both single-point and test-retest normal limits for H-reflex parameters of abductor brevis hallucis (ABH). The H reflex from the ABH muscle was recorded in 36 of 43 subjects, but could not be elicited in 7 of 11 subjects who were >60 years of age. The Hmax latency increased as height increased, whereas Hmax amplitude and Hmax/Mmax amplitude ratio decreased as age and height increased. The Hmax latency and Hmax/Mmax amplitude ratio, but not Hmax amplitude, proved to be reliable. The usefulness of the H reflex from ABH in the evaluation of S2 radiculopathies is described.

In this study, nerve excitability protocols were adapted for lower-limb recordings in 25 healthy subjects to enable comparison of excitability parameters between proximal and distal recording sites of the same nerve and between different nerves. Excitability parameters (stimulus–response curves, strength–duration properties, threshold electrotonus, a current–threshold relationship, and the recovery cycle) were recorded from tibialis anterior, extensor digitorum brevis, and abductor hallucis. Excitability recordings were technically possible from each site, and normative values were established for lower-limb nerves. In this process, inter- and intranerve differences in excitability properties were demonstrated: stimulus intensity and rheobase were reduced in recordings from proximal sites; the relative refractory period and late subexcitability were increased; superexcitability was reduced; and a relative “fanning-in” occurred for threshold electrotonus curves recorded from proximal sites. Such a length-dependent gradient in nerve excitability may underlie the greater tendency for ectopic activity to arise from the proximal segments of motor axons and may contribute to the length-dependent involvement of motor axons in the development of peripheral neuropathy. Muscle Nerve 29: 645–655, 2004

Electrical stimulation of the tibial nerve in the popliteal fossa evoked an M wave (10.9 ms) and a late reflex response (38.1 ms) in the plantar foot muscles of all 10 volunteers. The late response had a somewhat lower electrical threshold than the corresponding M wave (8.5 versus 9 mA), and reached a maximum of amplitude when the stimulus intensity was increased, but was strongly suppressed by further increased intensity. A more distal stimulation of the tibial nerve at the ankle shortened the onset latency of the M wave and lengthened that of the late response. The reflex was facilitated by activation of synergists and inhibited by activation of antagonists. We showed that the late response was contaminated neither by volume conducted activity from the soleus muscle, as shown by intramuscular recordings from the abductor hallucis muscle, nor by a F wave, as shown by double stimulation. In summary, we conclude that this late response in human plantar foot muscles corresponded to an H reflex, which may be used to assess alterations of distal motoneuronal excitability.

Motor unit number was estimated for the human abductor hallucis (AH) muscle in 11 subjects by counting the number of increments in surface electromyographic responses to progressive increases in current-pulse amplitude applied to the muscle-nerve. The average motor unit count for AH (43) was substantially smaller than that estimated for other human muscles. Consequently, motor unit activity should be readily recordable up to high forces in AH, making it well suited for studies of recruitment and rate coding.