Upper limb spasticity (ULS) is a common symptom after stroke and traumatic brain injury (TBI) and is associated with impaired self-care and additional burden of care [1-5]. Among several treatment strategies, guidelines recommend intramuscular botulinum toxin injections as a first-line treatment for adults with ULS [6-11].
Botulinum toxin type A (BoNT-A) injections may target upper extremity muscle groups from the shoulder, to decrease adductor and internal rotation tone, to the elbow, wrist, fingers, and thumb, to decrease flexor tone [12,13]. Specific muscle selection is based on the pattern of muscle overactivity, functional deficits, and patient goals . These goals include increased passive and active range of motion, improved function (feeding and dressing), easier care (palmar and axillary hygiene), and reduction of pain .
Evidence-based information on optimal dosing for clinical use is relatively sparse. Dosing is not interchangeable between different BoNT-A products; therefore, improving our understanding of product-specific dosing will minimize confusion among injectors and improve the quality of patient care .
Among BoNT-A formulations, abobotulinumtoxinA (Dysport; Galderma Laboratories, LP, Fort Worth, TX) has been shown to decrease muscle tone (as measured by the Modified Ashworth Scale [MAS]) [13-17] and pain  and to facilitate goal attainment  in adults with ULS. A recent systematic review  of 12 randomized controlled trials (RCTs) in ULS concluded that abobotulinumtoxinA (total dose range, 500-1500 U) was generally well-tolerated, with “strong evidence” to support reduced muscle tone.
This paper presents the results of a secondary analysis from a recently published large international clinical trial, demonstrating improved active range of motion after abobotulinumtoxinA treatment in adults with hemiparesis and ULS >6 months after stroke or TBI . This phase 3, randomized, double-blind, placebo-controlled study demonstrated that a total dose of either 500 U or 1000 U abobotulinumtoxinA injected in the upper extremity also resulted in decreased muscle tone and improvements in global physician-assessed clinical benefit compared with placebo.
Apart from a systematic measurement of active range of motion (XA) against finger, wrist, and elbow flexors, another unique aspect of the trial was the assessment of spasticity at the finger, wrist, and elbow flexor groups with the Tardieu scale (TS) [21,22]. The TS is a standardized evaluation used to assess the angle of arrest at slow speed (ie, passive range of motion, XV1) and the angle of catch at fast speed (XV3). The trial demonstrated improvements for finger, wrist, and elbow joints at week 4 in XV3 at both abobotulinumtoxinA doses and in XA at 1000 U; for the 500-U dose, improvements in XA were seen in the finger flexors. Both doses were associated with a favorable safety profile . This analysis aims to provide a detailed description of improvements in spasticity and the active range of motion for individual muscle groups by dose and to provide information on muscle-specific dosing, which can be used in future recommendations for injectors.