Somatosensory temporal discrimination in Parkinson's disease, dystonia and essential tremor: Pathophysiological and clinical implications

Objective: To investigate whether changes in the somatosensory temporal discrimination threshold (STDT) in Parkinson's disease (PD) and dystonia reflect the involvement of specific neural structures or mechanisms related to tremor, and whether the STDT can discriminate patients with PD, dystonia or essential tremor (ET). Methods: We tested STDT in 223 patients with PD, dystonia and ET and compared STDT values in patients with PD and dystonia with tremor with those of PD and CD without tremor. Data were compared with those of age-matched healthy subjects. Results: STDT values were high in patients with dystonia and PD but normal in ET. In PD, STDT values were similar in patients with resting or postural/action tremor and in those without tremor. In dystonia, STDT values were higher in patients with tremor than in those without tremor. The ROC curve showed that STDT discriminates tremor in dystonia from ET. Conclusions: In PD, STDT changes likely reflect basal ganglia abnormalities and are unrelated to tremor mechanisms. In dystonia, the primary somatosensory cortex and cerebellum play an additional role. Significance: STDT provides information on the pathophysiological mechanisms of patients with movement disorders and may be used to differentiate patients with dystonia and tremor from those with tremor due to ET.