Does the Diffusion Profile Differ Between Botulinum Toxin Type a Formulations? Implications for the Management of Post-Stroke Spasticity

Botulinum toxin type A is a first-line treatment for post-stroke spasticity, with selective action at nerve endings and minimal effects beyond the injection site. However, concerns about potential adverse reactions due to toxin diffusion and spread can significantly influence physicians' therapeutic decisions in managing post-stroke spasticity. Current evidence shows that while the main formulations of botulinum toxin type A have different molecular weights and sizes, they do not exhibit differing diffusion profiles. Instead, the key factors determining botulinum toxin type A diffusion and spread in post-stroke spasticity management are the dose (i.e., the actual amount of 150 kDa neurotoxin protein injected), dilution, and injection volume. Other injection-related factors, such as the needle gauge and injection speed, have also been suggested to have a secondary influence on botulinum toxin type A diffusion and spread. The needs of patients with post-stroke spasticity may vary, and depending on treatment goals, botulinum toxin type A diffusion and spread can be something to avoid or may offer therapeutic benefits by reaching a greater number of nerve terminals in the target muscle, enhancing the toxin's effect. These factors should be carefully evaluated in spasticity clinics.