局部肉毒桿菌素注射用來治療局部肌張力不全者，如頸肌張力不全，顏面神經痙攣及眼肌痙攣症，肉毒桿菌素經由阻斷神經肌肉間膽鹼的傳導，來減少局部肌肉的痙攣，同時也可對注射的遠端肌肉產生合併的舒緩效用，此種遠端效應的真正機轉並不清楚。很多假設試圖去解釋這種遠端效應，包括有1.局部擴散至遠端肌肉 2.經由血流循環 3.神經軸突的逆向傳導。 本研究乃是利用腦幹聽覺誘發電位的變化來證實其遠端效應，我們收集了16個頸部肌張力不全（9女10男），11個（7女4男）眼肌痙攣症及顏面神經痙攣的病人，在其接受肉毒桿菌注射前及注射後兩週，分別給予腦幹聽覺誘發電位檢查，結果顯示第一波的振幅在眼肌痙攣症這一組病人有明顯的增加（P<0.01），而第五波的振幅在頸肌張力不全這組有明顯增加（P<0.05），這可能的解釋，肉毒桿菌素可藉由臉部肌肉經由第七對神經的軸突逆向傳導，而致使蹬骨肌肉鬆馳，而使得在眼肌痙攣症這一組病人的第一波增強，而頸肌張力不全這一組的第五波增加可能由於肉肌梭纖維（Intrafusal fiber）的無力，而調控的感覺傳入腦幹上升徑路產生的變化所引起的，本研究正是以此來證實局部注射肉毒桿菌素所引發的遠端效應。 Local injection of botulinum toxin (BTX) are recognized as treatment of choice for for cervical dystonia and hemifacial spasm , blepharospasm. By long term blockade cholinergic neuromuscular transmission, BTX reduced localized muscle spasms, and can also produce effect at a distance from the injection site such as resolution of associated facial and oromandibular muscle contractions. However , the exact mechanism of these distant effect is still not clear . In the present study , we studied brain stem auditory evoked potential (BAEP) in n 16 patients（9 F,7 M）injected with BTX for spasmodic torticollis（ST）, and in 11 patients（7F, 4 M）treated for idiopathic blepharospasm or hemifacial spasm（IB/HFS）. BAEP were recorded twice before, and two weeks after the BTX injection. After BTX, mean amplitude values of the BAEP wave I increased in IB（p<0.01）, while they were slightly reduced in the ST group. Wave V amplitudes tended to increase after BTX in both IB and ST group（p<0.05）. Retrograde axonal transport of BTX from facial muscle via the 7th nerve can provoke weakening of stapedius muscle and thus induce the BAEP wave I amplitude increase in IB/HFS group. BTX induced intrafusal fibers paralysis within neck muscles may modify sensory afferent input control on the brain stem level resulting the wave V amplitude increase. We conclude the BAEP changes observed after BTX injection reflect distal effects of this treatment on the brain stem ascendant pathway and reflex.
