Temporal Discrimination and Proprioceptive Impairment in Parkinson's Disease: Evidence for Distinct Sensory Dysfunction Mechanisms.

BACKGROUND

Parkinson's disease (PD) is characterized by motor symptoms but also includes nonmotor impairments such as sensory disturbances. Temporal discrimination (TD) deficits have been repeatedly demonstrated, while proprioceptive dysfunction is also common in PD. The exact significance of these alterations, and whether they represent related aspects of a common pathophysiological process, remains elusive.

METHODS

We investigated somatosensory and kinesthetic TD as well as proprioceptive accuracy in 20 PD patients and compared 20 age- and sex-matched healthy controls (HCs). Somatosensory TD threshold (STDT) was assessed using paired cutaneous electrical stimuli and TD motor thresholds (TDMTs) by electrically induced wrist flexions. Proprioception was measured with two tasks requiring wrist flexion to predefined angles (LED task) or to reproduce angular ranges (ARROW task), without visual feedback. Clinical assessment comprised MDS-UPDRS III, Hoehn and Yahr stage, levodopa dosage, and disease duration.

RESULTS

PD patients exhibited significantly elevated thresholds compared to HC for both STDT (120.3 ± 42.3 ms vs. 80.8 ± 17.1 ms, p = 0.001) and TDMT (107.1 ± 43.7 ms vs. 77.0 ± 16.3 ms, p = 0.011). Proprioceptive errors were also higher in PD for the LED (6.7° ± 2.2° vs. 3.2° ± 1.9°, p < 0.001) and ARROW tasks (14.2° ± 3.4° vs. 2.1° ± 0.8°,p < 0.001). No significant correlations were observed between TD, proprioceptive measures, or clinical severity indices.

CONCLUSIONS

PD patients show pronounced impairments in both TD and proprioceptive accuracy, confirming sensory processing deficits beyond motor dysfunction. The absence of correlations suggests distinct mechanisms, highlighting the need for further neurophysiological research.