Intracortical inhibition and facilitation are impaired in patients with early Parkinson's disease:: a paired TMS study

Twelve patients with early Parkinson's disease (PD), none of whom had received any previous L-DOPA treatment, but using other antiparkinsonian drugs, were studied using transcranial magnetic stimulation (TMS). Contralateral and ipsilateral hemispheres were examined, with a focus on the more pronounced parkinsonian symptoms. The conditioning-test TMS paradigm (with a subthreshold conditioning stimulus and a suprathreshold test stimulus) was used through a stimulating round coil. Paired stimuli of short (3, 5 and 7 ms), medium (10, 15 and 20 ms), and long (100, 150, 200 and 250 ms) interstimulus intervals (ISI) were pseudo-randomly mixed with a single stimulus. The first interosseus muscle was used for the motor-evoked potential recordings. Ten healthy subjects (age and sex matched) were studied in the same manner to obtain normative data. When both groups were compared, the significant difference (reduction of the intracortical inhibition and facilitation) between the PD patients and the control group was found at the short and the medium ISI (3, 5, 7, 10, 15 and 20 ms) in both hemispheres (P < 0.05). The longer ISI produced non-significant differences between the two groups in intracortical excitability. There was a non-significant difference in the motor threshold. In conclusion, it can be supposed that both intracortical inhibition and facilitation are impaired in patients with early PD using other antiparkinsonian treatments than L-DOPA or dopamine agonists.