Knee pain patterns in older adults with or at risk for knee osteoarthritis (OA) may be associated with ascending and descending pain mechanisms, according to the results of a cross-sectional prospective cohort study published in Arthritis Care and Research.
In this study, patients (n=1284; ages, 50-79 years) who were at high risk of developing knee OA were recruited between 2003 and 2005. In addition, patients (n=1510; ages, 45-69 years) with OA (ie, Kellgren Lawrence grade £2), and reporting moderate or no knee pain were recruited between 2016 and 2017. Patients were assessed for peripheral and central ascending pain mechanisms, pressure pain thresholds, temporal summation, and descending modulation. Pain patterns were identified based on the Intermittent and Constant OA Pain questionnaire (ICOAP).
In this cohort, mean age was 63.9 years, 57% of participants were women, and the mean body mass index was 29.5 kg/m2. Mean ICOAP scores were: 10.3 for intermittent pain, 2.2 for constant pain, and 6.6 for the total scale. In this cohort, 67% reported not experiencing knee pain (intermittent or constant), 26% reported experiencing intermittent knee pain, 7% reported experiencing constant knee pain, and 18% had unpredictable pain.
Enhanced pain sensitization (ie, greater temporal summation) was found to be associated with higher ICOAP scores on the intermittent subscale (β estimates: intermittent, 0.54; 95% CI, 0.03-1.04; constant, -0.03; 95% CI, -0.38 to 0.31; total score, 0.28; 95% CI, -0.08 to 0.63). Lower pain sensitization (ie, greater pressure pain threshold values) was found to be associated with lower ICOAP scores at the wrist (intermittent: b, -1.44; 95% CI, -1.92 to -0.97; constant: b, -0.64; 95% CI, -0.92 to -0.36; total: b, -1.08; 95% CI, -1.40 to -0.76) and at the knee, and with constant +/- intermittent pain vs intermittent pain only (odds ratio [OR], 0.80; 95% CI, 0.68-0.93). Patients who reported more sensitization to pain were more likely to experience unpredictable pain (OR, 1.08; 95% CI, 1.00-1.18).
Participants with vs without conditioned pain modulation were more likely to experience constant pain (Constant ICOAP score: b, 0.83; 95% CI, 0.25-1.40). Adequate conditioned pain modulation was associated with reporting constant +/- intermittent pain vs intermittent pain only (OR, 1.53; 95% CI, 1.07-2.19).
Limitations of this study include the fact that the duration of pain symptoms for each patient was not known and that variables which were unaccounted for may have triggered ‘unpredictable’ pain.
“Taking a mechanistic approach to understanding pain in knee OA may provide the basis for a targeted and personalized approach to pain management, particularly when paired with validated clinical symptoms,” noted the study authors. “We found that different pain sensitization-related mechanisms were associated with different pain patterns, particularly intermittent vs constant pain.”
Carlesso L C, Law L F, Wang N, et al. The association of pain sensitization and conditioned pain modulation to pain patterns in knee osteoarthritis. [published online September 3, 2020] Arthritis Care Res (Hoboken). doi:10.1002/acr.24437