ASSESSMENT OF CUTANEOUS SENSORY AND AUTONOMIC AXON REFLEXES IN RHEUMATOID-ARTHRITIS

Objective-To assess sensory function in skin overlying the joints of p atients with rheumatoid arthritis, in relation to the pain and tendern ess which commonly arises in structures not directly involved in the i nflammatory process. Methods-An intradermal injection of capsaicin 0.0 5 mu g in 10 mu l was made over the wrists and forearms of 40 patients with rheumatoid arthritis and 46 control subjects. Axon reflex vasodi latation was measured using laser Doppler flowmetry. Cholinergic sympa thetic function was assessed by measuring axon reflex sweating induced by a single intradermal injection of nicotine 0.5 mu g in 0.1 ml. Res ults-Capsaicin induced axon reflex vasodilatation over the wrists was found to decrease with age in normal subjects (r=-0.62, p<0.001). In p atients with rheumatoid arthritis, capsaicin induced axon reflex vasod ilatation was significantly greater over the wrists, but not the forea rms, when compared with age matched normal controls (p<0.01). A minima l correlation between axon reflex vasodilatation and visual analogue p ain score was apparent in the rheumatoid group (r=-0.37, p<0.05). Nico tine induced sweating responses were similar in the rheumatoid and nor mal groups, and both showed a linear age related decline. Conclusions- The results show a selective of capsaicin induced vasodilation in skin overlying joints in patients with rheumatoid arthritis. This suggests that the activity of a subpopulation of periarticular small sensory f ibres is altered, which may explain, at least in part, some of the cli nical findings in this disorder.