Background Paroxysmal kinesigenic dyskinesia (PKD) is characterized by recurrent brief episodes of chorea and dystonia induced by sudden movement.Whether the central nervous system is hyper- or hypoexcitable in PKD remains undetermined.The aim of our study was to compare the somatosensory evoked potential (SEP) recovery cycle,a marker of somatosensory system excitability,in PKD patients and controls.Methods Twenty-four PKD patients (mean age of (20.0±5.3) years; 21 males,3 females) and 18 control age-matched subjects (mean age of (22.0±5.0) years; 17 males,1 female) were studied.The stimuli were delivered to the median nerve in the affected dominant arm in patients and in the dominant arm in controls.The change in SEP amplitude was measured after paired electrical stimulation at interstimulus intervals (ISIs) of 5,20,and 40 ms.The SEPs evoked by S2 (test stimulus) were calculated by subtracting the response to S1 (the conditioning stimulus) from the response to a pair of stimuli (S1 + S2),and their amplitudes were compared with those of the control response (S1) at each ISI.Analysis of variance (ANOVA) or equivalent was used for non-parametric data.Results In patients,the P27 amplitude after the single stimulus (S1) was significantly larger than that after the control stimulus.The (S2/S1)x100 ratio for P14 and N30 SEPs did not differ significantly between PKD patients and normal subjects at ISI of 5 ms but were significantly higher in patients at ISIs of 20 and 40 ms (P＜0.05).Conclusions Somatosensory system disinhibition takes place in PKD.The finding of reduced suppression of different SEPs,each thought to have a different origin,suggests an abnormality of intracortical and subcortical inhibitory circuits.