Pain sensitivity and pain reactivity in osteoarthritis

Objective. To assess experimental pain sensitivity and compare the inflammatory response to pain in 26 osteoarthritis (OA) patients and 33 age-and sex-matched controls from the general population in order to examine the nature of the association between pain and inflammation in OA. Methods. The participants underwent psychophysical pain testing to assess pain sensitivity in response to heat, cold, and mechanical stimuli. Blood samples were taken at baseline and at 4 time points after testing to determine the effect of acute pain on C-reactive protein (CRP), interleukin-6 (IL-6), IL-1β, and tumor necrosis factor α levels. Results. OA patients had lower pressure pain thresholds (P ≤ 0.003) and higher heat pain ratings (P ≤ 0.04) than controls across multiple body sites. OA patients had higher CRP levels than controls (P = 0.007). CRP levels did not change in response to pain testing. Although not statistically significant, OA patients tended to have higher IL-6 levels than controls (P = 0.12). IL-6 levels increased after pain testing in OA patients and controls (P < 0.0001), but the amount of increase was not different between the 2 groups. Among OA patients, heightened pain sensitivity was associated with elevated CRP and IL-6 levels (P ≤ 0.05). Conclusion. Compared with controls, OA patients are more sensitive to experimental pain at multiple body sites. IL-6 levels in OA patients and controls exhibited reactivity to acute painful stimuli, increasing at similar rates after psychophysical pain testing.