Follow-up of interhemispheric differences of motor evoked potentials from the 'affected' and 'unaffected' hemispheres in human stroke.

We analysed motor-evoked potentials (MEPs) from the hand muscles during focal transcranial magnetic stimulation (TCS) in both the affected (AH) and the unaffected (UH) hemispheres of 17 monohemispheric stroke patients followed-up in subacute stage. Recording sessions were performed at 2 (T1 session) and 4 (T2 session) months from acute stroke. Clinical and functional scores were evaluated. An age-sex matched group of 20 healthy subjects have been referenced. In T1, relaxed MEPs from AH were smaller than UH (p<0.001) and normals (p<0.001). In T2, an increase of AH relaxed-MEPs amplitude was observed, combined with an improvement of clinical and functional scores (p<0.001). On the other hand, the amplitude of contracted MEPs from the AH in T1 was larger than in the normal group. This parameter decreased toward normal limits in T2, provided that the amplitude of the MEPs from the AH improved, while it further increased when TCS of the AH continued to fail in eliciting MEPs. This phenomenon was statistically combined with clinical improvement of disability and neurological scores. Recovery of the excitability AH threshold with progressive 'balancing' of the UH hyperresponsiveness represents a good prognostic parameter for clinical outcome of hand motor function.