Botulinum toxin type A has been approved for spasticity management in poststroke patients. The adverse effects are generally of two types: those related to local injection; and those related to the systemic effects from spread of the toxin. Contralateral weakness after botulinum toxin A treatment is a rarely reported adverse effect. We report the case of a 33-year-old female who had been receiving regular injections of incobotufinum toxin A due to spasticity of the right limbs after a hemorrhagic stroke. A switch was made to abobotulinum toxin A with an overall conversion ratio of 1:3.83. The patient presented contralateral upper limb paresis, especially of the deltoid muscle, in the second week post-injection. The electroneuromyography showed neuromuscular block due to botulinum toxin A. She recovered completely after eight months. A switch between different formulations of botulinum toxin type A should prompt caution when carrying out unit conversions. Distant side effects may appear, including paresis in the contralateral limbs.

Background/Objectives: The aim of this study was to compare the efficacy and safety of a single cycle of incobotulinumtoxinA versus placebo in pooled data from older patients (aged ≥65 years) with upper limb spasticity (ULS). Methods: This study was a post hoc analysis of pooled data from seven prospective, multicenter, phase II or III trials of incobotulinumtoxinA in adult patients aged ≥65 years from across the world with post-stroke ULS or upper and lower limb spasticity, including a subgroup with moderate-to-severe ULS. Changes from baseline in ULS severity were evaluated using the (modified) Ashworth Scale across different spasticity patterns at 4 and 12 weeks after incobotulinumtoxinA injection. Results: In 267 older patients with ULS, including a subgroup of 207 with moderate-to-severe ULS, all ULS patterns statistically analyzed (elbow flexion, thumb-in-palm, clenched fist, wrist flexion, and pronated forearm) were improved more by incobotulinumtoxinA than placebo at week 4 (p < 0.05). For most of these patterns, the difference remained significant at week 12 (p < 0.05). IncobotulinumtoxinA was generally well tolerated. Conclusions: This study, which analyzed data from the largest cohort of older patients in the literature, provides information regarding the use of incobotulinumtoxinA in ULS, the efficacy and favorable safety profile of incobotulinumtoxinA for the treatment of ULS in older patients, particularly in those with moderate-to-severe spasticity, was confirmed.