Background/Purpose:  Patients with knee osteoarthritis (OA) often start with acute intermittent, activity-related pain, which evolves to additionally experiencing chronic, persistent pain; why this transition happens is not known. It is possible that peripheral and central sensitization, which is associated with knee pain severity in knee OA, contributes to the transition from solely acute intermittent pain to chronic, persistent pain. We assessed whether a marker of sensitization, pressure pain threshold (PPT), was associated with change from intermittent to chronic, persistent pain over time in a large cohort of older adults with or at risk of knee OA.

Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded cohort longitudinal cohort of persons with or at high risk of knee OA. Subjects had a standardized somatosensory evaluation of mechanical pressure pain thresholds (PPT) at the wrist and patella and completed pain questionnaires at baseline and two years later. PPT was assessed with an algometer (1cm² tip, 0.5 Kg/sec) as the point at which the subject felt the pressure change to slight pain. The average of 3 PPT trials was categorized into sex-specific tertiles. Lower PPT indicates more sensitization/pain sensitivity; at a site of disease (e.g., knee), it indicates peripheral sensitization, while at a site without disease (e.g., wrist), it indicates central sensitization. The Intermittent and Constant OA Pain (ICOAP) instrument assesses presence and severity of intermittent and constant pain, and for intermittent pain, its frequency (5-point Likert scale for each). Using the knee-specific ICOAP, pain patterns were defined as: 1) no intermittent or constant pain; 2) intermittent pain only (of at least mild severity occurring at least sometimes); and 3) constant pain (of at least mild severity) with or without intermittent pain. Among subjects with either no pain or intermittent pain only at baseline, we evaluated the relation of baseline PPT to incidence of constant pain using logistic regression. We compared the two highest PPT tertiles with the lowest tertile as there appeared to be a threshold effect. All analyses were adjusted for age, sex, BMI, depressive symptoms, catastrophizing, and clinic site.

Results: There were 1951 subjects included (mean age 68, 60% female, mean BMI 31), of whom ~8% developed constant pain over two years. A low level of peripheral sensitization, as reflected by medium and high knee PPT tertiles, was associated with a lower risk of developing incident constant pain [OR: 0.64 (0.40-1.00, p= 0.05)]. Similarly, a low level of central sensitization as measured by wrist PPT was also associated with a lower risk of incident constant pain [OR: 0.52 (0.32-0.86, p=0.01)].

Conclusion: Lower levels of peripheral and central pain sensitization are associated with lower rates of evolution or progression of the pain pattern from intermittent or no pain to constant pain over time. These findings support the hypothesis that sensitization plays an important role in changing a patient’s pattern and severity of OA-related pain. These findings have implications for understanding the transition from acute to chronic pain.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/relation-of-pain-sensitization-to-the-evolution-from-intermittent-to-chronic-persistent-pain-in-knee-osteoarthritis-the-multicenter-osteoarthritis-study/