Exploring somatosensory temporal discrimination deficits in rheumatoid arthritis: associations with disease activity and functionality

Objective- Somatosensory deficits in rheumatoid arthritis (RA) have not been adequately investigated, despite their potential impact on an individual's functioning. This study aims to evaluate the central processing of sensory stimuli in RA patients using the Somatosensory Temporal Discrimination (STD) test and to investigate any possible associations between sensory status, self-reported disability, and disease activity. Methods- The study included twenty patients with RA and twenty healthy subjects. RA disease activity was assessed using the Disease Activity Score 28-joint count Erythrocyte Sedimentation Rate (DAS28-ESR). The Health Assessment Questionnaire Disability Index (HAQ) was used to assess self-reported disability. A constant current stimulator was employed to measure minimal detection stimulus intensity (MDSI) and Somatosensory Temporal Discrimination Thresholds (STDT) from the dorsum of the participant's hands. Results- The STDTs for the right (114.50 ± 28.41 ms) and left hands (112.62 ± 20.89 ms) in RA patients were significantly higher compared to those of healthy subjects (right hand: 80.00 ± 35.16 ms; left hand: 80.39 ± 37.34 ms) (right hand: p = 0.021; left hand: p = 0.034). The mean MDSIs for the right (3.17 ± 0.62 mA) and left hands (3.24 ± 0.80 mA) of RA patients were higher than those of the control group (right hand: 2.91 ± 1.00 mA; left hand: 2.81 ± 0.98 mA), although these differences were not statistically significant (right hand: p = 0.353; left hand: p = 0.145). No significant correlations were found between STDTs, MDSIs, DAS28-ESR and its components, and HAQ in the RA group (p > 0.05). Conclusions- Our study provides novel insights into how sensory information is processed centrally in RA, highlighting changes in sensory processing not fully captured by traditional sensory function measures. Clinically, prolonged STDT indicates impaired temporal discrimination capacity, reflecting deficits in central sensory integration. Although STD impairment does not directly correlate with current disease activity or functional disability scores, the findings underscore the need for targeted rehabilitation strategies to address sensory processing deficits.