P74-T Reduced hand dexterity in Parkinson’s disease correlates with the level of short-latency intracortical inhibition impairment

Abstract

Background In Parkinson’s disease (PD), primary motor cortex (M1) shows number of impairments in excitability and plasticity. However, there has been scarce attempts to check whether there is a link between these impairments and impaired hand dexterity in PD. Methods In a group of 29 PD patients (Hoehn & Yahr stage range 1–4), measures of M1 excitability (short latency intracortical inhibition [SICI] and intracortical facilitation [ICF], and plasticity (paired associative stimulation [PAS] protocol) were collected. They were correlated with results on the Perdue pegboard task (PPT), as a measure of hand dexterity, as well as with scores on a standard clinical scale (motor section of the Unified Parkinson’s Disease Scale [UPDRS]). Patients were tested off medication, after an overnight withdrawal. All measurements were carried out on the worst affected hand. Results Increase in MEP size immediately after and 30 min after the PAS protocol did not correlate with either PPT score or UPDRS motor cores 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 It seems that in untreated PD patients there is a direct link between intracortical inhibition and hand dexterity. Lack of adequate short-latency intracortical inhibition most likely interferes with fine selection of movements which is of crucial importance for hand dexterity.