Characterization of joint pain in human OA.

Characterization and differentiation of joint pain is difficult. Though degenerative changes in joints are frequent causes of pain in hip and knee, these changes are not always painful, and other possible causes of pain must also be considered. In degenerative changes in the spine, the problem is even more complex, as peripheral neuropathic pain, caused by mechanical compression and/or leakage of cytokines irritating nerve roots may be difficult to differentiate from nociceptive pain from intervertebral joints, discs or muscles. We know now that nociceptive pain has often referred to areas of pain with numbness and parestesthethic sensations, previously regarded as characteristic for neurogenic pain. Furthermore, in patients with painful coxarthrosis quantitative sensory testing (QST) has shown disturbed sensory thresholds not only in regions adjacent to the affected hip but also contralaterally. These sensory disturbances, previously noted in neuropathic pain, normalized after successful surgery with relief of pain, thus confirming the relation to the hip joint. Patients with painful coxarthrosis also have moderately increased substance P activity in cerebrospinal fluid. Thus the findings show some similarities with fibromyalgic patients with highly increased substance P in cerebrospinal fluid and sensory disturbances. In conclusion, joint pain has a profound impact on the sensory system and need a multimodal approach.