Motor disinhibition in affected and unaffected hemisphere in the early period of recovery after stroke
Introduction
It has been documented in animal models that acute focal brain damage is often followed by functional cortical motor and sensory reorganization close to the damaged areas and associated with behavioural motor recovery (Nudo et al., 1996, Xerri et al., 1998). Recent research has demonstrated enhanced excitability in the neighbourhood of the damaged area after ischaemic lesions in rats (Schiene et al., 1996, Buchkremer-Ratzmann et al., 1996, Buchkremer-Ratzmann and Witte, 1997). Involvement of cortical inhibition has also been found in remote areas to the lesions and in the contralateral unaffected hemisphere in animal models (Buchkremer-Ratzmann and Witte, 1997, Reinecke et al., 1999). In these brain areas, paired pulse inhibition studies including γ-amino butyric acid (GABA) receptor investigation, indicate a decrease in GABAergic inhibition (Mittmann et al., 1994, Schiene et al., 1996, Neumann-Haefelin et al., 1995, Luhmann, 1996). Functional imaging studies in patients recovering from hemiparetic stroke have described an enlarged activation volume in brain regions close and remote to the lesion, including the contralateral hemisphere (Weiller et al., 1992, Weiller et al., 1993, Cramer and Bastings, 2000). These studies, however, which yield information regarding changes in areas of the motor cortex, provide no information on the inhibitory and facilitatory mechanisms underlying these plastic changes.
Transcranial magnetic stimulation (TMS) is an important tool for exploring the excitability of the human motor cortex in vivo. TMS permits non-invasive painless evaluation of the cortical representation areas of muscles by mapping the motor cortex. Enlargement of motor areas has been documented using TMS in stroke patients during recovery (Traversa et al., 1997, Traversa et al., 1998, Traversa et al., 2000) and after specific rehabilitative treatment (Liepert et al., 1998). As regards the functional imaging, TMS maps, which inform about changes in areas of the motor cortex, provide no information on inhibitory and facilitatory mechanisms underlying these modifications in motor areas. The technique of paired magnetic stimulation is particularly sensitive in detecting intracortical mechanisms. Several studies have found that intracortical inhibition (ICI) and intracortical facilitation (ICF) reflect the excitability of distinct inhibitory and excitatory interneuronal circuits within the motor cortex (Kujirai et al., 1993, Ziemann et al., 1996a, Ziemann et al., 1996b). Liepert et al. have documented in a first study (Liepert et al., 2000a) the absence of motor inhibition by paired TMS in stroke patients in the acute stage only in the affected hemisphere and in a second study he reported the reduced motor inhibition in the unaffected hemisphere (Liepert et al., 2000b). The authors postulated that this disinhibition might be indicative of compensatory mechanisms involved in recovery-related reorganization.
The main objective of the present study was to test changes in intracortical excitability in patients in close and remote areas to the cerebrovascular lesion. We investigated the excitability of the hand motor cortex in both hemispheres by paired magnetic stimulation in patients with moderate to severe hemiparesis after an acute cerebrovascular monohemispheric lesion in order to verify involvement of the unaffected hemisphere in the early period of functional recovery.
Section snippets
Subjects and methods
Fifteen patients (4 women, 11 men) aged from 56 to 75 years (mean age 64) were entered into the study. The inclusion criteria were: (1) monohemispheric lesions; (2) computerized tomography (CT) or magnetic resonance imaging (MRI) documenting a single monohemispheric lesion; (3) age below 80 years; and (4) first ever attack. The exclusion criteria were concomitant neuropathies, systemic vasculopathies, epilepsy and dementia making patients uncooperative. Furthermore patients with intracerebral
Clinical score
After 1 month functional and neurological scores showed a significant improvement in all patients (ANOVA, P<0.001, Table 1, Fig. 1). The patients were divided into two groups with poor and good recovery using a Barthel index score of 65 as the cut-off at T2. Group A: patients with good motor recovery at T2 (5 patients: n=1–5). Group B: patients with poor motor recovery at T2 (10 patients: n=6–15) (Table 1).
Global functional evaluation using a Barthel index and neurological score as measured
Discussion
The study shows that the ICI of the motor areas of the hand muscles on both sides is abnormally reduced in the early period after stroke and depends on the functional recovery. The main finding is that after 1 month ICI in the unaffected hemisphere showed a return to normal values in patients with significant motor recovery, while it remained abnormal in the unaffected hemisphere in patients with poor motor recovery. These findings are clearly in agreement with the study of Liepert et al., 2000a
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