| Local injections of botulinum toxin type A are now widely used in the treatment of various types of focal dystonia and clinically similar conditions. The therapeutic effects of the toxin can be largely explained by its well known blocking action at the neurorriuscular junction, which remains fairly confined to the injected muscles. A subtle impairment of endplate function, however, can be observed also in remote muscles, probably caused by hematogenous spread of the toxin. In addition, tracer studies have shown that the toxin can be transported retrogradely in the motor axons to the motoneurons and may even leave the cell bodies. Little is known, however, about potential effects of the toxin on motoneurons or on segmental connectivity, although several studies in animals have provided some evidence for an action at spinalinterneurons and for an impairment of the Renshaw inhibition. Additionally, a modification of the reciprocal inhibition has been demonstrated in humans.A sensitive measure of the functional state of motoneurons in man is the F-wave, which is generated in these cells by antidromic excitation. F-wave parameters such as latency, size, and persistence ( rate of occurrence ) depend on the state of excitability of the motoneurons and of their connectivity. This prompted us to carry out an F-wave study in a small group of torticollis spasmodicus patients treated with local injections of botulinum toxin type A, and describe changes that can not be readily explained by an impairment of neuromuscular transmission.Materials and methods1. SubjectsAll subjects were informed of the scientific character of the F-wave studies and gave their consent. 29 patients with idiopathic torticollis spasmodicus (TC) were studied. 29 healthy volunteers participated in the study. Age, sex and height Did not differ significantly between the two groups (P>0.05) .2. Local BTX-A injectionsBTX-A was injected into various neck muscles in TC patients with the guidance of electromyogram. The used dose varied from 100U to 200U(mean 147.2±42.3U) .3. ElectrophysiologyThe F-wave studies were carried out immediately before (time 0) and 1 and 12-16 weeks after the injections, respectively, in the TC patients. F- and M-waves were recorded bilaterally for the ulnar nerve from the abductor digit! quinti muscle and for the tibiai nerve from the musculus abductor hallucis using conventional techniques. We determined the amplitudes (compound muscle acton potentials) and distal motor latencies of the M-waves of the abductor digiti quinti muscle and the musculus abductor hallucis and the corresponding motor conduction velocities of the ulnar nerve at the forearm and of the tibiai nerve over the head of the fibula. For the F-waves, the shortest, the longest and the mean latency of 20 trials and the persistence were calculated. The same studies were carried out in the healthy volunteers.4. Medical statistic analysisFor all measured parameters, mean values and standard deviations (SD) were calculated for each nerve studied at time 0, 1 week and 12-16 weeks after injection in TC patients and in healthy volunteers.Hypothesis testing methods used included one-way ANOVA and Pearson correlation test. In the statistical analysis of this study, probabilities lower than 0.05 were taken as significant.Results1. Basic Information29 healthy volunteers participated in the study and all completed the measurement of F- and M-waves. 29 patients with idiopathic torticollis spasmodicus (TC) participated in the study, 12 cases completed the measurement of F- and M-waves three times, 4 cases did not completed this measurement in the second time, and 15 cases did not completed this measurement in the third time.2. M-wavesComparison with the healthy volunteers, the amplitudes, distal motor latencies and motor conduction velocities of the M-waves of the ulnar nerve and the tibial nerve were unchanged in TC patients (P>0.05) . the amplitudes, distal motor latencies and motor conduction velocities of the M-waves of the ulnar nerve and the...
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