Time course analysis of the effects of botulinum toxin type a on elbow spasticity based on biomechanic and electromyographic parameters

OBJECTIVE: To quantify changes of elbow spasticity over time after botulinum toxin type A (BTX-A) injection in the upper extremity of stroke patients.

DESIGN: Before-after trial in which the therapeutic effects were followed up at 2, 6, and 9 weeks after the BTX-A injection (Botox).

SETTING: Hospital.

PARTICIPANTS: Chronic stroke patients (N=8) with upper-limb spasticity.

INTERVENTION: BTX-A was injected in upper-limb muscles, including the biceps brachii.

MAIN OUTCOME MEASURES: Treatment effects were quantified as the changes in the velocity and the length dependence of hyperexcitable stretch reflexes. Manual sinusoid stretches of the elbow joint at 4 frequencies (1/3, 1/2, 1, 3/2Hz) over a movement range of 60 degrees were performed on patients by using a portable device. The Modified Ashworth Scale (MAS), biomechanic viscosity, and the reflexive electromyography threshold (RET) of the biceps brachii were used to evaluate the degree of hypertonia.

RESULTS: The statistical analyses of the MAS score, biomechanic viscosity, and RET revealed a significant decrease in spasticity after the injection (all P<.05). Moreover, our quantitative parameters (biomechanic viscosity, RET) revealed small changes in spasticity after the BTX-A injection that could not be observed from clinical MAS evaluations. Five of 8 subjects showed a maximal reduction in spasticity (in terms of biomechanic viscosity value) within 6 weeks after the injection, whereas it was notable that all subjects exhibited peak RET values at either 2 or 6 weeks after the injection with variable degrees of relapse of spasticity.

CONCLUSIONS: Early relapse of spasticity (within 9 weeks of the injection) can be detected from biomechanic and neurophysiologic assessments in a clinical setup. These quantitative indices provide valuable information for clinicians when making decisions to perform additional rehabilitation interventions or another BTX-A injection in the early stages of treatment.