Do flexible inter-injection intervals improve the effects of botulinum toxin a treatment in reducing impairment and disability in patients with spasticity?

In patients treated with botulinum toxin-A (BoNT-A), toxin-directed antibody formation was related to the dosage and frequency of injections, leading to the empirical adoption of minimum time intervals between injections of 3months or longer. However, recent data suggest that low immunogenicity of current BoNT-A preparations could allow more frequent injections. Our hypothesis is that a short time interval between injections may be safe and effective in reducing upper limb spasticity and related disability. IncobotulinumtoxinA was injected under ultrasound guidance in spastic muscles of 11 subjects, who were evaluated just before BoNT-A injection (T0), and 1month (T1), 2months (T2) and 4months (T3) after injecting. At T1, in the case of persistent disability related to spasticity interfering with normal activities, patients received an additional toxin dose. Seven subjects received the additional dose at T1 because of persistent disability; 4 of them had a decrease of disability 1month later (T2). Rethinking the injection scheme for BoNT-A treatment may have a major impact in the management of spasticity and related disability. Future studies with larger sample sizes are warranted to confirm that injection schedules with short time intervals should no longer be discouraged in clinical practice.