Association of Pain Sensitization and Conditioned Pain Modulation to Pain Patterns in Knee Osteoarthritis
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OBJECTIVES: To examine the cross-sectional association of ascending pain mechanisms (APM), implicated in pain sensitization (PS), and descending pain modulation with pain patterns and unpredictability of pain. METHODS: The Multicenter Osteoarthritis (OA) Study is a longitudinal cohort of older adults with or at risk of knee OA. Peripheral and central APM were assessed using quantitative sensory tests (QST); pressure pain thresholds (PPTs) using a handheld pressure algometer (knee/peripheral and wrist/central), temporal summation (TS) using weighted probes (wrist/central). Descending modulation was assessed by conditioned pain modulation (CPM) using PPTs and a forearm ischemia test. Pain patterns were characterized based on responses to the Intermittent and Constant OA Pain (ICOAP) questionnaire: 1) no intermittent or constant pain; 2) intermittent pain only; 3) constant pain only; and 4) combined constant and intermittent pain. A question regarding frequency assessed unpredictable pain. We assessed the association of QST measures to pain patterns using regression models with generalized estimating equations. RESULTS: There were 2794 participants (mean age 63.9, BMI 29.5 kg/m2 , 57% female). Lower PS (by wrist PPT) OR = 0.80 (95% CI 0.68, 0.93) and adequate CPM, OR = 1.45 (1.10, 1.92) were associated with having constant +/- intermittent pain compared with intermittent pain only. Higher PS (by PPT and TS) was associated with higher likelihood of unpredictable pain. CONCLUSIONS: Knee pain patterns appear to be related to peripheral +/- central facilitated APM, and descending modulatory mechanisms. These findings highlight the need for a broader approach to understanding pain mechanisms by symptomatic disease progression.
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