Histopathologic Changes after Injection of Botulinum Toxin A in the Rat

Kim, Soo Young; Chung, Seong Moon; Chang, Suk Choo

Abstract

Recently, Botulinum toxin A has been used effectively in nonsurgical treatment of facial wrinkles. This toxin produce predictable and reversible paralysis in facial mimetic muscles. To investigate the histological changes in skeletal muscle following botulinum toxin injection, 27 female rats (200 - 250 gm) were injected with single dose of 50 of 0.1/ml botulinum toxin A (Botox, manufactured by Allergan Inc.) in right gastrocnemius muscle. Three months after the first toxin injection, second injection was given at the same area. The muscle biopsy was made in the 1st, 2nd, 3rd week, and the 1st, 2nd, 3rd month after the first injection and in the 1st, 2nd, 3rd week, and the 1st, 2nd month after the second injection. The pathologic findings showed atrophy of myofibers, cell proliferation in intermyofibers, and internalization of sarcolemmal nuclei. The incidence and severity of these changes increased gradually by 4 weeks and then recovery of paralysis occurred slowly. The pathologic findings of the second injection showed slightly severer than the first injection, but the progress of pathologic changes were the same as the first injection. In conclusion, the present study demonstrates that extensive myopathic changes develop following botulinum toxin injection. But, botulinum toxin A produces no persistent histologic change in muscle fiber. Its therapeutic effect is reversible and transient.