Electrophysiologic Responses of Neuromuscular Junction by High Dose of Botulinum Toxin A Injection: Local and Distant Effects

ABSTRACT

OBJECTIVE: The purpose of this study was to measure the local and distant effects of BTX-A of different dosage through the electrophysiologic study. METHOD: Sixteen Sprague-Dawley rats were used and divided into four groups by the dosage of BTX-A (Botox , Allergan Co.) 2, 4, 6, 8 U for each of the four rats. BTX-A was injected into tibialis anterior (TA) muscles. Slow rate (3 Hz) and fast rate (20 Hz) repetitive nerve stimulation test (RNST) was performed before and after BTX-A injection. The schedule of postinjection was as follows 2 days after the injection, every seven days till 10 weeks postinjection, once a month for 4 months. RESULTS: In the fast rate RNST of the treated TA muscle, dose-dependent increments were seen on the 2nd day postin jection and thereafter dose-dependent decrements appeared and weakened over the course of time. In the slow rate RNST of the treated TA, dose-dependent decrements were observed through ten weeks postinjection in all groups. In the fast rate RNST of the untreated TA, incremental responses were produced in all groups in a dose-dependent manner. In the slow rate RNST of the untreated TA, there were no changes. CONCLUSION: The BTX-A injection causes local paralysis in the treated muscles and presynaptic dysfunction of the neuro muscular junction in the distant untreated muscles in a dosedependent manner. This study could not be differentiated between neuromuscular dysfunction, myopathy or neuropathy through these RNST studies.