Variability and predictability of functional efficacy of botulinum toxin injection in leg spastic muscles

Botulinum toxin injection reduces spasticity level. However, the effects on gait parameters and daily living activities remain controversial, and the prediction of results remains poorly evaluated. The aim of this open study was to investigate these effects, and the predictability of results. Forty-seven injections were given to 47 patients with stroke (males: 24; mean age: 51.7), in the soleus, gastrocnemius, tibialis posterior and anterior, and flexor digitorum longus, with a global dose of 300 U (Botox®). Each was evaluated at day 1 (D1), day 15 (D15), month 2 (M2) and month 5 (M5). We observed a significant but moderate reduction in spasticity (Ashworth) of the ankle plantar flexors (0.72/5) and dorsiflexors, which was greater at D15, and an improvement in distal positioning in the upright situation. Upright balance and gait (Functional Ambulation Categories) were improved, especially at M2 and in the barefoot condition. Gait velocity and step length with usual aids (10 m) were discretely increased, and this was especially evident in about 15 patients. We also found improvement in the Rivermead Motor Assessment. Patients reported better foot positioning, facilitation in limb propulsion, and better static and dynamic balance. For each assessment, high variability in the effects was also shown. Improvement in functional tests was partially predicted by age (negative relation), delay since stroke (negative relation), gender (better in men), spasticity of hip adductors and knee extensors (negative relation), active ankle dorsiflexion (positive relation) and heel-ground distance (positive relation). In conclusion, the effects on spasticity, balance and gait were relatively modest, and with a large variability between patients. Functional improvement could be partially predicted by several general or specific factors, the knowledge of which is important in the selection of patients to be injected, and for future trials aiming to demonstrate the efficacy of botulinum toxin injection.