Sensory temporal discrimination threshold values for the patients with Parkinson's disease, its relation to clinical findings and role in the pathophysiology of Parkinson's disease

The somatosensory temporal discrimination threshold (STD), the shortest time interval that allows two temporally separated 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 (PD), abnormally increased STD may contribute to the pathophysiology of motor deficits.We aimed to explore the clinical significance of STD in PD patients. Twenty-one PD patients and 20 age-matched normal controls were included. Patients were recruited from the Movement Disorders and Parkinson's Disease Unite of Neurology Department, Medical School of Gazi University. The STD values were measured in the forehead and chin areas. Ascending and descending interstimuli intervals were evaluated for each point. The disease severity was assessed by Unified Parkinson's Disease Rating Scale (UPDRS). Demographic characteristics of the patients, disease duration, types and doses of drugs used, the non-motor symptoms associated with the disease were also recorded. STD values of the PD patients were higher than those of the controls. The STD values did not correlate with UPDRS motor scores.Our experiments showed that STD threshold improved significantly when patients were receiving medication. Thus suggesting that dopaminergic therapy is important in modulating STD and improves STD thresholds. Nigrostriatal dopaminergic neurons may cause abnormalities in the central processing of kinesthetic and cutaneous sensory information and may worsen motor symptoms due to abnormal kinesthetic and postural control. Rehabilitation programmes targeting these findings may contribute to the improvement of motor symptoms especially posture and gait in PD patients.