Pain in osteoarthritis from a symptom to a disease

Pain is a ubiquitous symptom in osteoarticular diseases, occurring much more commonly than stiffness or disability. Osteoarthritis (OA) of the knee, hand, or hip affects ∼20–30% of adults in various populations [1] and is dramatically increasing in many countries, mostly related to age and obesity, leading to an increased number of people having OA pain, and creating a huge burden related to pain, disability, and healthcare costs [2].

Paradoxically, in comparison to the extensive research focus on inflammation and immunity in joint diseases, for many years OA pain pathophysiology received little attention, and numerous important research questions remain unanswered [3]. OA-related pain is a specific disease, with a complex pathophysiology, including neuropathic peripheral and central abnormalities, together with local inflammation involving all joint structures. Qualitative findings emphasize that it is not a stable and linear condition [4], that pain experience is independent of structural modifications, and that the quality of pain in OA is important to consider, aside from its intensity. OA-related pain is modulated by many factors, including the individual patient's psychological [5] and genetic [6] factors, as well as the theoretical role of meteorological influences. Recent neuroimaging findings have improved our knowledge about the central mechanisms of OA pain, especially in persistent cases [7].

From the patient's point of view, OA pain, like many other pain conditions, is associated with numerous misconceptions and erroneous beliefs about its causes and effective management. In fact, there are major difficulties in getting patients to describe their OA pain: they may think nobody wants to hear about it, or perhaps they feel the need to preserve their self-image and social image. Some people live their lives according to self-imposed stoicism, and some perceive OA as a complex, ever-changing, illogical disease associated with aging [4]. Recently, the IASP and WHO have classified OA pain as a chronic secondary musculoskeletal pain [8], defining a real disease with epidemiological research. Specific questionnaires recently developed for OA pain, assessing all OA-related pain dimensions, may also help to define pain phenotypes.

There is an urgent need to develop better analgesic drugs for people with OA pain, since the analgesics currently prescribed for OA, paracetamol, opioids, and NSAIDs, frequently fail to provide adequate pain relief, or patients may discontinue them because of adverse events. One may expect that future treatments for OA pain will be developed more specifically according to OA pain pathophysiology and pain phenotypes. This review, based on literature and personal research on OA pain over the last 15 years, will summarize the most pertinent discussions and findings on this complex and disabling pain condition.

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