P290 Reduced hand dexterity in parkinson’s disease patients is associated with impaired intracortical inhibition

Abstract

Objectives To check whether hand dexterity in Parkinson’s disease (PD) patients is linked with motor cortex excitability and plasticity. Background Hand dexterity is impaired in PD patients. Primary motor cortex (M1) shows number of impairments in excitability and plasticity. There has been scarce attempts to check whether there is a link between impaired neurophysiological measures and impaired hand dexterity. Methods Measures of M1 excitability, short latency intracortical inhibition (SICI) and intracortical facilitation (ICF), and plasticity, relative increase in size of motor evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS) following paired associative stimulation (PAS) protocol, were collected in a group of 29 PD patients (Hoehn and Yahr stage range 1–4). They were correlated with results on the Perdue pegboard task (PPT), as a measure of hand dexterity, carried out with the worst affected hand, as well as with scores on standards clinical scale, motor section of the Unified Parkinson’s Disease Scale (UPDRS). Patients were tested off medication, after an overnight withdrawal. Results Increase in MEP size immediately after and 30 min after the PAS protocol did not correlate with either PPT score or UPDRS motor scores and two derived scores, lateralised UPDRS and bradykinesia score (for the worst affected side). Same was with ICF. However, there was a significant correlation between amount of SICI and PPT score (Spearman R = 0.42, p = 0.023) – the larger the inhibition the higher the PPT scores; SICI did not correlate with other clinical measures. Conclusion Hand dexterity in PD patients off medication seems to be associated with intracortical inhibition. This may suggest that the lack of adequate short-latency intracortical inhibition, by interfering with fine selection of movements, negatively affects hand dexterity. It is an interesting hypothesis which would certainly need further verification.