Botulinum B toxin as an alternative to botulinum A toxin: a histologic study.

Histochemical effects of botulinum B toxin were studied on fibers from longissimus dorsi muscle in Albino rabbits and compared to effects produced by botulinum A toxin. Acetylcholinesterase staining, muscle fiber size analysis, and ATPase staining indicated botulinum B toxin produced a denervation gradient and field similar to that produced by botulinum A toxin. At 5 weeks postinjection with botulinum B toxin, analysis showed muscle fiber size variability, and diffuse acetylcholinesterase fiber staining comparable to botulinum A toxin at the injection site. Muscle sections taken at 4.0 cm for analysis showed statistically significant decreased fiber size variability and contraction of acetylcholinesterase staining pattern for both immunotypes. In addition, the denervation reflected by histochemical staining and fiber size analysis appeared transient and lasted for approximately 3 months for both immunotypes. These findings suggest botulinum B toxin produces pharmacologic effects on innervation of striated muscle similar to botulinum A toxin. Because immunologic tolerance has been demonstrated after therapeutic botulinum A toxin injections, further clinical studies need to be conducted with other immunotypes of toxin with no cross-reactivity to type A.