Abnormal temporal discrimination threshold in patients with multiple system atrophy

The temporal discrimination threshold (TDT), the shortest time interval that allows two temporally separated successive stimuli to be perceived as two different stimuli, is a constituent of kinesthetic sensation. Intact kinesthesia is a necessity for well-controlled voluntary movements. In patients with Parkinson's disease and dystonia, abnormally increased TDT has been reported and it may contribute to the pathophysiology of motor deficits. We explored the integrity and clinical significance of TDT in patients with multiple system atrophy (MSA). A total of 30 de novo patients with MSA and 11 age-matched normal controls were included. The TDT values were measured in the feet with four different paradigms (ascending and descending interstimuli intervals; same and different point stimulation). The Unified Parkinson's Disease Rating Scale (UPDRS) Motor and the International Cooperative Ataxia Rating Scale (ICARS) scores were measured for parkinsonian and cerebellar deficits, respectively. Means of the TDT values of the patients with MSA were higher than those of the controls. The TDT values correlated with UPDRS Motor scores independent of ICARS scores. Among the parkinsonian motor deficits, only the UPDRS Motor subscores representing bradykinesia correlated with the TDT values. In patients with MSA, abnormal somatic sensory processing seems to be associated with damage to the nigrostriatal dopaminergic and/or striatal neurons.