Nerve injection injury with botulinum toxin

The therapeutic use of botulinum toxin (Botox) is increasing in popularity. Previous studies have shown that various drugs, especially when injected intrafascicularly, can cause major nerve damage. This study evaluates the potential for neurotoxicity of botulinum toxin in a rat sciatic nerve model. Lewis rats were randomly assigned to one of six groups (n = 10/group). Group 1, 2, and 3 rats received, respectively, an intrafascicular, extrafascicular, and extraneural injection of 50 μl of botulinum toxin (50 UI/ml). Group 4, 5, and 6 rats received 50 μl of 10% phenol as a positive control. Five animals received saline as a negative control. Animals were sacrificed at 2 and 7 weeks. Nerves were harvested and processed for histology and morphometry. Nerves in all botulinum toxin groups retained a normal architecture without cellular infiltration or demyelination. The number and diameter of fibers, the thickness of myelin, and the percentage of neural tissue were comparable with normal controls. Nerves injected intraneurally with phenol presented with severe damage, demyelination, and inflammation at 2 weeks and showed signs of early regeneration at 7 weeks. This study demonstrates that in a rat model, even direct intraneural injection of botulinum toxin caused no damage. This information should encourage the reconstructive surgeon to consider broader applications of this drug.