Investigating Inducible Muscle Overactivity in Acquired Brain Injury and the Impact of Botulinum Toxin A.

OBJECTIVE

To investigate the pattern of change in muscle overactivity during repetitive grasp/release using dynamic computerized dynamometry (DCD; objective 1) and the effect of botulinum toxin A (BTX-A; objective 2).

DESIGN

Secondary analysis of an observational cohort study.

SETTING

Hospital outpatient spasticity management service.

PARTICIPANTS

A convenience sample (N=65), comprising adults with upper motor neuron syndrome affecting the arm after acquired brain injury (ABI; n=38) and participants without ABI (n=27).

INTERVENTIONS: After clinical assessment, a subgroup of participants with ABI (n=28) underwent BTX-A injections as part of their spasticity management.

MAIN OUTCOME MEASURES: Post hoc DCD data processing extracted the values of minimum force generation between 10 sequential contractions. The pattern of change was analyzed.

RESULTS

The ABI injected group exerted greater force at baseline than both other groups (ABI injected=1.04 kg, ABI noninjected=0.74 kg, participants without ABI=0.53 kg; P=.011). After the first contraction, minimum force values increased for all groups and were greatest in the ABI injected group. With subsequent cycles, the group without ABI showed a linear pattern of decreasing force generation, whereas both ABI groups showed a quadratic increasing pattern, which was of greater magnitude in the ABI injected group. After injection, values for the ABI injected group showed a 51% reduction in inducible muscle overactivity (P=.003) to magnitudes similar to those of the ABI noninjected group.

CONCLUSIONS

This study showed that hand relaxation deteriorated during repetitive movements in people with spasticity, a feature hypothesized to adversely influence everyday hand function. After BTX-A injection, the magnitude but not the pattern of this inducible muscle overactivity improved.