P 160 Temporal discrimination and temporal discrimination motor thresholds – association with age, proprioception, and polyneuropathy

Abstract

Introduction Temporal discrimination threshold (TDT) and temporal motor discrimination threshold (TMDT) are measures of somatosensory processing indicating the shortest time interval at which two stimuli applied to skin or muscle, respectively, are detected to be asynchronous. TDT and/or TDMT have been shown to be increased in patients with movement disorders, like essential tremor, dystonia, or Parkinson”s disease. However, the meaning of these findings is still quite unclear. Here, we assessed the association of TDT and TDMT with age, proprioception, and polyneuropathy (PNP). Materials and methods 54 healthy subjects (age 29–75 years) and 15 patients with neurophysiologically confirmed PNP were included. TDT was tested with surface electrodes placed over thenar or dorsal foot region, respectively. TDMT was measured via an insulated tungsten needle microelectrode inserted at the motor point of flexor carpi radialis (FCR) or tibialis anterior (TA) muscle. Pairs of subsequent electric stimuli with varying interstimulus intervals (ISI) were provided, and discrimination thresholds were defined as the shortest ISI at which subjects were able to identify two separate stimuli. Proprioception of upper and lower limbs was assessed by custom-built devices, basically consisting of a goniometer without direct visual feedback of the respective extremity and its movements (flexion/extension). Subjects were instructed (i) to point to LED markers attached to the outside of the device, (ii) to move in proportion to arrows of different length shown on a computer screen, and (iii) to estimate their limb position after passive hand movements. Part of the assessment was conducted under dual task condition (tone-counting task). Pointing (or estimation) error (in degree) was taken as a measure of proprioceptive performance. Results In healthy subjects higher age was associated with higher TDT in every tested condition (right hand [ r = 0.358, p r = 0.359, p r = 0.591, p r = 0.505, p r = 0.317, p = 0.05]). In PNP patients, TDMT and TDT were significantly higher at all sites as compared to controls ( p Discussion Our results point to an association between higher age and poorer capacity of discriminating somatosensory stimuli. The correlation of performance in a particular pointing task of the hand with lower TDMT suggests this measure as a potential surrogate marker of proprioceptive function. Both TDT and TDMT were markedly increased in PNP patients, indicating their clinical meaning in diseases with affection of the proprioceptive system. This might also be the pathophysiological link to previous findings of elevated thresholds in movement disorders.