Beyond spasticity reduction: botulinum toxin-a injection is associated with changes in abnormal flexor synergies of the upper limb in chronic stroke.
Michiyuki Kawakami, Daisuke Ito, Ken Azuma and 3 others
PMID 42012215WHAT IT FOUND
Botulinum toxin injections in chronic stroke patients reduced elbow spasticity and improved an index of abnormal flexor synergy.
The study did not show a change in maximum voluntary shoulder flexion angle. These findings are from a small, uncontrolled cohort and cannot confirm causality or clinical benefit.
Key findings
01The abnormal flexor synergy index significantly increased from 82.3% to 86.5% after injection, indicating reduced involuntary elbow flexion during shoulder movement.
02Maximum voluntary shoulder flexion angle did not change significantly after injection.
03MAS elbow flexor scores and MAS finger PIP flexor scores showed significant reductions, while wrist and MP finger flexor changes were not significant after adjustment.
STILL TO COME
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What it does not show
The study was retrospective and uncontrolled, so it cannot prove that the injection caused the observed changes. The sample size was small (n = 28) and from a single centre, limiting generalizability. Detailed procedural parameters of the injections (e.g., dilution, volume) and concomitant rehabilitation intensity were not consistently documented. The minimal detectable change for the abnormal flexor synergy index was not established, so the clinical relevance of the observed change is uncertain. Follow-up was only approximately two months, so long-term effects are unknown.
Declared interests
The authors declared no conflicts of interest. The study was funded by the Japan Society for the Promotion of Science (JSPS KAKENHI).
The easy way to misread this
Do not interpret the improvement in the abnormal flexor synergy index as evidence of functional recovery. The study was uncontrolled, the change was small, and maximum voluntary shoulder flexion did not improve. Furthermore, non-responders experienced a decline in shoulder flexion, suggesting potential weakness from the injections.
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