Strategies in Motor Stroke Rehabilitation
To the Editor:
We read with interest the report by Woldag et al about increased corticomotoneuronal excitability targeting muscles in the paretic hand of chronic stroke patients during voluntary contraction of the healthy hand.1 The authors interpreted their results as supportive of the concept that use of the unaffected hand may exert a beneficial effect on paretic hand function.
We raise your attention to 2 issues that impact on this interpretation. First, measurements of corticomotoneuronal excitability provide mechanistic information on brain activity but do not represent a surrogate marker of paretic hand function. This report carefully describes changes in excitability. In the absence of measures of motor function, it is difficult to assess the functional relevance of these results on neurorehabilitation. For example, voluntary contraction of the healthy hand, as implemented in this study and leading to increased motor excitability targeting the paretic hand, might increase spasticity or elicit other possible detrimental effects on motor control that were not tested.
Second, please note that the increase in excitability targeting the paretic hand of patients was significantly lower than that seen in controls. This decreased ability to facilitate the paretic hand is consistent with a recent report of abnormally high inhibitory drive from the intact to the affected motor cortices in patients with chronic stroke moving the affected hand, which correlated with poor motor performance.2 Both findings support the alternative interpretation that increased motor activity of the intact hand may not be beneficial to recovery of the paretic hand, a proposal supported by clinical and experimental evidence including: (1) usefulness of intact hand immobilization as adjuvant to paretic hand training during constraint-induced therapy;3 (2) findings of improved motor function in the paretic hand with anesthesia of the intact hand;4 and (3) imaging data that demonstrated a negative correlation between magnitude of contralesional activation and functional recovery5 in patients with chronic stroke.
Clearly, additional work is required to sort out these issues. One attractive approach would be the acknowledgement that mechanisms of recovery after chronic stroke may differ depending on factors like chronicity, lesion size or site, and degree of impairment. If so, apparently contradictory results may be accounted for by heterogeneous patient populations, inclusion criteria, and experimental designs. Future studies should keep in mind apparently conflicting evidence, for example favoring bilateral arm training on one hand and training of only the paretic hand with constraint of the healthy limb on the other, in focused prospective experimental designs that can teach us which patients benefit the most from each intervention. Finally, combining physiological results with direct measures of paretic hand function is likely to provide the highest yield in understanding the mechanisms of functional recovery after stroke.
Woldag H, Lukhaup S, Renner C, Hummelsheim H. Enhanced motor cortex excitability during ipsilateral voluntary hand activation in healthy subjects and stroke patients. Stroke. 2004; 35: 2556–2559.
Calautti C, Baron JC. Functional neuroimaging studies of motor recovery after stroke in adults: a review. Stroke. 2003; 34: 1553–1566.
The authors of the Letter to the Editor point to the important issue that voluntary activation of the healthy hand in stroke patients may not be beneficial to functional recovery of the paretic hand. The interpretation of the results of our study is in line with this point of view. As we have stated, occupational and physiotherapy must eagerly focus on the paretic hand by using intensive motor practice if there is any voluntary movement of the paretic hand. The main conclusion of our study is that compensatory use of the unaffected hand to achieve the highest possible degree of independence does not exert an inhibitory impact on the excitability of the motor cortex of the affected side. Because it was not the focus of our study, we have never stated that voluntary use of the unaffected hand may have a beneficial effect on paretic hand function. If the message of our paper in this respect was misleading, we are grateful to the authors to make this issue plain.