A functional threshold for long-term use of hand and arm function can be determined: predictions from a computational model and supporting data from the Extremity Constraint-Induced Therapy Evaluation (EXCITE) Trial

Abstract

Background: Although spontaneous use of the more-affected arm and hand after stroke is an important determinant of participation and quality of life, a number of patients exhibit decreases in use following rehabilitative therapy. A previous neurocomputational model predicted that if the dose of therapy is sufficient to bring performance above a certain threshold, training can be stopped.

Objective: The aim of this study was to test the hypothesis that there exists a threshold for function of the paretic arm and hand after therapy. If function is above this threshold, spontaneous use will increase in the months following therapy. In contrast, if function is below this threshold, spontaneous use will decrease.

Methods: New computer simulations are presented showing that changes in arm use following therapy depend on a performance threshold. This prediction was tested by reanalyzing the data from the Extremity Constraint-Induced Therapy Evaluation (EXCITE) trial, a phase III randomized controlled trial in which participants received constraint-induced movement therapy for 2 weeks and were tested both 1 week and 1 year after therapy.

Results: The results demonstrate that arm and hand function measured immediately after therapy predicts, on average, the long-term change of arm use. Above a functional threshold, use improves. Below this threshold, use decreases.

Limitations: The reanalysis of the EXCITE trial data provides a "group" threshold above which a majority of patients, but not all, improve spontaneously. A goal of future research is to provide the means to assess when patients reach their individual threshold.

Conclusion: Understanding of the causal and nonlinear relationship between limb function and daily use is important for the future development of cost-effective interventions and prevention of "rehabilitation in vain."

Figure 1.

Simulated data of use of the affected arm (A) just after therapy and (B) 3,000 trials after therapy as a function of performance (reach directional error in the model) just after therapy for 125 simulated subjects with different lesion sizes and locations. (C) Comparison of the sigmoidal fit of use just after therapy and 3,000 trials after therapy. The intersection of the 2 curves gives the threshold in arm performance above which use increases and below which use decreases. The upward arrow indicates that 89.1% of the simulated subjects above threshold showed increased arm use after therapy. The downward arrow indicates that 87.1% of the simulated subjects below threshold showed decreased arm use after therapy. Note that we reversed the x axis, to compare with the data of Figure 2.

Figure 2.

Use of the more-affected arm, as recorded by the Motor Activity Log Amount of Use (MAL AOU) subscale: (A) 1 week after therapy and (B) 1 year after therapy as a function of arm and hand function (Functional Ability Scale [FAS]) 1 week after therapy for subjects of the EXCITE trial. (C) Comparison of the sigmoidal fit of use 1 week after therapy and 1 year after therapy. The intersection of the 2 curves gives the functional threshold (FAS score=3.44) above which uses increases and below which use decreases. The upward arrow indicates that 68.2% of subjects above threshold showed increased arm use after therapy. The downward arrow indicates that 63.5% of subjects below threshold showed decreased arm use after therapy.