i106 Chronic musculoskeletal pain and the pitfalls of assuming fibromyalgia

Abstract

Fibromyalgia is a disorder of pain processing in patients with psychological vulnerability. Sleep disturbance and fatigue are integral features. A recent meta-analysis of UK studies concluded that chronic pain affected between one third and one half of the population. Most of the cohort had MSK pain although neuropathic or other non-MSK pain was included. For many, fibromyalgia has almost become a shorthand description for unexplained chronic pain. However the prevalence of fibromyalgia is only approximately 5% of patients if the ACR criteria are employed. It is therefore interesting to consider the similarities and differences between fibromyalgia and other chronic MSK pain. Although the 2010 ACR criteria for fibromyalgia dispensed with examining tender points, some clinicians have continued to rely on counting the number of tender points described in the 1990 ACR criteria in order to make the diagnosis of fibromyalgia. This may be misleading. Hyperalgesic or tender points are also tender in healthy individuals by simply increasing the pressure. The tender point examination may therefore be viewed simply as a surrogate method of measuring pain threshold. Given that chronic pain is known to lower the pain threshold, counting tender points in a patient with pain limited to the low back is inappropriate. In addition, some patients with primary enthesitis may have pain in several sites and finding tenderness in these sites may lead to an erroneous diagnosis of fibromyalgia in a patient with psoriatic spondyloarthritis. The converse may apply in patients with fibromyalgic rheumatoid arthritis who are in remission but have widespread tenderness contributing to a high DAS score and leading to inappropriate treatment with biologic drugs. Functional imaging in fibromyalgia has demonstrated abnormal neural connectivity between pain pathways and other neural networks that is highly correlated with pain severity. However, abnormal neural connectivity is not unique to fibromyalgia and has also been demonstrated in other chronic pain conditions such as irritable bowel syndrome and chronic low back pain. These data suggest that there may be similar mechanisms of pain at least in some patients.