Post-stroke reorganization of hand motor area: a 1-year prospective follow-up with focal transcranial magnetic stimulation
Introduction
Motor recovery after stroke is largely variable and often difficult to predict from clinical and imaging findings. Among other paraclinical methods, transcranial magnetic stimulation (TMS) has been proposed to predict motor outcome after a stroke (Catano et al., 1995, Rapisarda et al., 1996, Bastings et al., 1997, Escudero et al., 1998, Pennisi et al., 1999). Most authors agree that persistent response to TMS in the early days after ischemic stroke is an indicator of good motor outcome. Recent studies outlined the existence of ‘a plastic’ reorganization of the cortical motor output that still operates between 2 and 4 months after an acute mono-hemispheric stroke (Trompetto et al., 2000). A contribution of the so-called unaffected hemisphere through ipsilateral pathways has been proposed based on clinical (Fisher, 1992), neurophysiological (Trompetto et al., 2000, Alagona et al., 2001), and neuro-imaging data (Chollet et al., 1991, Weiller et al., 1992, Silvestrini et al., 1995). Other mechanisms have been advocated: motor messages from motor cortex could be conveyed to spinal motor neurons through reticulospinal pathways whose connections are bilateral at the spinal cord level (Fries et al., 1991, Meyer et al., 1991) but their functional role in recovery from stroke remains controversial. The recovery process may also involve distinct mechanisms at different times after the brain injury. Some discrepancies among previous reports may be due to inclusion in some series of patients with different motor deficits at stroke onset, variable localizations of the infarcts and electrophysiological testing at different stages.
The aims of the present study were to investigate the neural mechanisms underlying functional recovery following stroke and to confirm the usefulness of early TMS in predicting motor outcome after stroke. The nature of recovery processes may also change along the course of the illness. Studying patients over a long period of time after stroke (more than 4 months after stroke as previously reported (Trompetto et al., 2000) may thus provide useful information. Therefore, we undertook a 1 year follow-up study of clinical and electrophysiological parameters of stroke patients with severe hand palsy at onset. All had a single ischemic lesion in the middle cerebral artery (MCA) territory.
Section snippets
Normal subjects
Twenty age-matched healthy volunteers (7 men, 13 women; aged 45–80 years, mean: 62.45 years) chosen among relatives or staff members of our department gave their informed consent for this protocol.
They had no prior neurological disease and their neurological examination was normal.
Stroke patients
The local Ethical Committee approved the study and informed consent was obtained from all patients or from a close relative. Thirty-one first-ever stroke patients (16 men, 15 women, aged 17–91 years, mean: 65.32) were
Normal subjects
Cortical mapping procedures were successfully completed in all normal subjects (18 right-handed, two left-handed). Results are summarized in Table 2.
There was no significant difference of motor thresholds to TMS of the FDI muscle responses between the dominant and non-dominant hemisphere. The amplitudes of maximal motor responses on both sides were also comparable. Only, the excitable area on the dominant side was significantly broader than on non-dominant side (P=0.02, paired t). The centers
Discussion
Motor evoked potentials are often heavily reduced in amplitude or completely abolished after a hemispheric stroke (Rossini et al., 1987, Heald et al., 1993a, Heald et al., 1993b, Caramia et al., 1991, Cicinelli et al., 1997a, Cicinelli et al., 1997b, Binkofski et al., 1996). Few studies have correlated characteristics of MEP in acute stroke and final clinical outcome. In general, it was observed that patients with relatively preserved MEPs on the affected side in the early days after stroke
Acknowledgements
This study was supported by a grant from the ‘Fondation Léon Frédéricq’ for Medical Research at the University of Liège. Valérie Delvaux was funded as clinical research fellow by the Medical Research Fund of the ‘Centre Hospitalier Universitaire’ of Liège.
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