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.