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Background and objectives: Our study aimed at examining the long-time inflammatory effects of rheumatoid arthritis (RA) as chronic immune-mediated disease on pain sensation and neuropathy development compared to healthy subjects (HS).
Methods: We used the quantitative sensory testing (QST) protocol of the German Research Network on Neuropathic Pain and Electroencephalography (EEG)–based contact heat evoked potentials (CHEPs) before and after topical capsaicin application. We recruited 16 RA patients in remission or low disease activity state (mean age: 59.38 years [± 10.18]) and 16 healthy subjects (mean age: 56.69 years [± 8.92]).
Results: The application of capsaicin cream on the thigh provoked a stronger effect in HS for both mechanical and heat pain thresholds (MPT and HPT, resp.), according to the area under the receiver operation characteristic (AUROC) (HS: HPT: 0.8965, MPT: 0.7402; RA: HPT: 0.7012, MPT: 0.6113). We observed contrary effects regarding changes in CHEPs (HS: g*max = − 0.65; RA patients: g*max = 0.72).
Conclusion: As the overall effect of topical capsaicin application was higher in HS for QST, we suggest the existence of a sensitization of TRPV1 channels in RA patients caused by long-time chronical inflammation, despite a lack of clinical signs of inflammation due to adequate treatment. The effect in CHEPs probably uncovers neuropathic symptoms. The effect of topical capsaicin on HPTs and CHEPs can act as a marker for the extent of sensitization and the development of neuropathic symptoms. Further studies are needed to prove if our proposed method can act as a marker for the success of anti-inflammatory treatment.
Assessment of individual therapeutic responses provides valuable information concerning treatment benefits in individual patients. We evaluated individual therapeutic responses as determined by the Disease Activity Score-28 joints critical difference for improvement (DAS28-dcrit) in rheumatoid arthritis (RA) patients treated with intravenous tocilizumab or comparator anti-tumor necrosis factor (TNF) agents. The previously published DAS28-dcrit value [DAS28 decrease (improvement) ≥ 1.8] was retrospectively applied to data from two studies of tocilizumab in RA, the 52-week ACT-iON observational study and the 24-week ADACTA randomized study. Data were compared within (not between) studies. DAS28 was calculated with erythrocyte sedimentation rate as the inflammatory marker. Stability of DAS28-dcrit responses and European League Against Rheumatism (EULAR) good responses was determined by evaluating repeated responses at subsequent timepoints. A logistic regression model was used to calculate p values for differences in response rates between active agents. Patient-reported outcomes (PROs; pain, global health, function, and fatigue) in DAS28-dcrit responder versus non-responder groups were compared with an ANCOVA model. DAS28-dcrit individual response rates were 78.2% in tocilizumab-treated patients and 58.2% in anti-TNF-treated patients at week 52 in the ACT-ion study (p = 0.0001) and 90.1% versus 59.1% at week 24 in the ADACTA study (p < 0.0001). DAS28-dcrit responses showed greater stability over time (up to 52 weeks) than EULAR good responses. For both active treatments, DAS28-dcrit responses were associated with statistically significant improvements in mean PRO values compared with non-responders. The DAS28-dcrit response criterion provides robust assessments of individual responses to RA therapy and may be useful for discriminating between active agents in clinical studies and guiding treat-to-target decisions in daily practice.