Background and purpose: Botulinum toxin (BTX) treatment can relieve focal arm spasticity after stroke, presumably through dynamic changes at multiple levels of the motor system, including the cerebral cortex. However, the neuroanatomical correlate of BTX spasticity relief is not known and should be reflected in changes of cortical activation during motor tasks assessed using repeated functional magnetic resonance imaging (fMRI).
Methods: Four patients (2 males, 2 females, mean age 25.5 years) with hemiplegia and distal arm spasticity after chronic ischemic stroke sparing the motor cortex were studied. fMRI during mental movement simulation of the impaired hand was performed in 2 sessions before and 4 weeks after BTX treatment. The change in arm spasticity was assessed using the modified Ashworth scale (MAS).
Results: BTX treatment significantly decreased arm spasticity across the group (mean MAS change 2.1). Whereas fMRI during imagined movement pre-BTX treatment showed extensive bilateral network of active areas, post-BTX activation was confined to the midline and contralateral sensorimotor cortices. The pre- > post-BTX contrast revealed a significant decrease in activation of the posterior cingulate/precuneus region after BTX treatment.
Conclusion: This small study suggests that structures outside the classical motor system, such as the posterior cingulate/precuneus region, may be associated with the relief of poststroke arm spasticity.