Skin inflammatory reactions to capsaicin in rheumatoid arthritis patients compared to healthy controls

Previous studies have examined the role of sensory nerves and neural mediators in symmetrical joint inflammation and autoimmunity in rheumatoid arthritis (RA). In this study, we sought to examine the association between capsaicin skin test and disease activity in RA patients.

Eighty RA patients (case group) and 20 healthy volunteers were enrolled in this experiment. The subjects in case group were calcified to newly diagnosed patients and those previously diagnosed with RA. A topical solution of capsaicin (0.075%) was applied on the volar forearm during the skin test, and evaluations were done after 5, 10, and 20 min. The parameters recorded in capsaicin skin test were time to tingling, area of induration (cm²), and area of redness (cm²).

A faster capsaicin skin reaction was observed in healthy controls compared to the case group (p=0.02). Newly diagnosed and previously diagnosed RA patients were not significantly different in terms of reaction latency (p=0.06). The redness area after 15 (p=0.04) and 20 (p=0.001) min was significantly larger in previously diagnosed RA patients than in newly diagnosed ones. The ​​area of redness and time to tingling did not show any difference between active and inactive RA patients, but after 15 and 20 min, the area of redness was significantly greater in inactive RA patients compared to active RA patients (p=0.01 and p=0.03, respectively).

This study suggested that capsaicin skin test is not an efficient tool for the examination of synovial inflammation and disease activity in RA.