Background/Purpose: Both animal and human studies have suggested that both peripheral and central sensitization may occur in nociceptive pain states such as OA.  This distinction is important since although peripheral sensitization is due to ongoing peripheral nociceptive input and would respond to more aggressive use of peripherally-directed therapies, if central sensitization or centralized pain is identified, this may indicate that treatments aimed at the central nervous system may be more helpful.  Using quantitative sensory testing (QST), the presence of peripheral sensitization is suggested when there is tenderness (i.e. mechanical hyperalgesia/allodynia) localized to the knee, whereas if both the knee and a distant site are tender this is suggestive of central sensitization.  Although both peripheral and central sensitization are typically identified using sophisticated pain research tools such as quantitative sensory testing (QST) or functional brain imaging, recent studies have suggested that the 2011 Survey Criteria for FM, used as a continuous rather than dichotomous variable, may be helpful in identifying individuals who have centralized pain.  We hypothesized that if this was the case, individuals with knee OA with higher FM scores should have a stronger relationship between the mechanical pain threshold at the knee and that at a distant “neutral” site such as the thumb.  

Methods: As part of a larger study of analgesic outcomes following total knee arthroplasty, a subset of 63 individuals (ages 42 – 81, 24 males, 39 females) scheduled to undergo arthroplasty had a mechanical pain threshold assessed at both their painful knee and dominant thumb, and also completed the 2011 FM criteria.  We then performed a tertile split of the cohort using FM scores, with the lowest tertile of 22 individuals having FM scores of 0-3, the middle tertile of 23 individuals having scores of 4-7, and the highest tertile of 18 individuals having scores of 8 or greater. 

Results: Using non-parametric correlations (Spearman’s rho), we found that in the lowest FM tertile, there was no significant relationship between the mechanical threshold at the knee, and that measured at the thumb (r_s = .305, p = .167).  The middle FM tertile showed a stronger but still statistically insignificant correlation (r_s = .352, p = .099).  However, individuals with KOA in the highest FM tertile displayed a highly significant correlation between the threshold at the knee, and that measured at the thumb (r_s = .651, p =.003).

Conclusion: These data lend further evidence that the 2011 FM Survey Criteria, when used us a continuous rather than dichotomous measure, serve as a surrogate measure for the presence of central sensitization in KOA.  Together with previously published studies from this same cohort suggesting that this measure is also strongly predictive of both opioid and surgery non-responsiveness, this suggests that this measure may provide useful in both research and clinical practice in identifying individual who might benefit from more centrally-directed therapies such as centrally acting analgesics, or non-pharmacological therapies.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-2011-fibromyalgia-fm-criteria-are-helpful-in-identifying-central-sensitization-in-knee-osteoarthritis/