Distinct pain sensitization mechanisms dictate constant vs. intermittent pain in knee OA
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Among patients with, or at risk for, knee osteoarthritis, knee pain patterns could potentially be linked to peripheral ascending pain mechanisms and descending modulatory mechanisms, according to data published in Arthritis Care & Research.
“The pain experience in patients with knee osteoarthritis changes over time,” Lisa C. Carlesso, PT, PhD, of McMaster University in Ontario, Canada, told Healio Rheumatology. “It is initially experienced intermittently with weight bearing activities but progresses to become more persistent with unpredictable flares. We wanted to better understand why this change may occur.”
To analyze the link between ascending pain mechanisms, implicated in pain sensitization, and descending pain modulation with pain patterns and unpredictability of pain, Carlesso and colleagues examined data from the Multicenter Osteoarthritis Study, a longitudinal cohort of older adults with or at risk of knee OA.
Researchers studied peripheral and central ascending pain mechanisms using quantitative sensory tests, including pressure pain thresholds using a handheld pressure algometer, and temporal summation using weighted probes. Meanwhile, descending modulation was analyzed using conditioned pain modulation and pain pressure thresholds, as well as a forearm ischemia test.
Pain patterns were characterized based on responses to the Intermittent and Constant OA Pain (ICOAP) questionnaire. Pain categories included no intermittent or constant pain, intermittent pain only, constant pain only and combined constant and intermittent pain. Unpredictable pain was assessed through a question regarding frequency. The association of quantitative sensory tests with pain patterns was examined using regression models with generalized estimating equations. In all, Carlesso and colleagues analyzed data on 2,794 participants.
According to the researchers, lower pain sensitization (OR = 0.8; 95% CI, 0.68-0.93) — assessed by wrist pressure pain thresholds —and adequate conditioned pain modulation (OR = 1.45; 95% CI, 1.1-1.92) were associated with having constant pain, either with or without intermittent pain, compared with intermittent pain only. Higher pain sensitization — assessed using pressure pain thresholds and temporal summation — was associated with a higher likelihood of unpredictable pain.
“We found that people having constant and unpredictable pain had more pain sensitization or alterations of signaling in their nervous systems, compared to those with intermittent pain,” Carlesso said. “These results indicate, for the first time, the potential underlying mechanism in the nervous system responsible for why people experience these different pain patterns with knee osteoarthritis. Understanding the mechanisms contributing to the pain experience will ultimately help us tailor our treatments to the individual and, in this case, their pain pattern.”
“In addition, this data supports the clinical relevance of using information beyond pain severity, such as whether the pain is intermittent, constant or unpredictable, to inform a person’s care,” she added. “By understanding the different mechanisms that may be contributing to these different pain patterns, we can use interventions that will help re-establish normal signaling in their nervous systems to diminish their pain response.”
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