Central pain mechanisms in the rheumatic diseases: future directions.

Abstract

Pain is a prominent component of many rheumatologic conditions, and is the result of a complex physiologic interaction of central and peripheral nervous system signaling that results in a highly individualized symptom complex. Pain is frequently categorized as acute or chronic (generally greater than three months duration). Chronic pain is not simply acute pain that has lasted longer, and is more likely to be influenced by input from the central nervous system, whereas acute pain is often attributable primarily to inflammation and/or damage in peripheral structures (i.e., nociceptive input). The prominent role of central factors in chronic pain is highlighted by the fact that there is currently no chronic pain condition in which the degree of tissue inflammation or damage alone (e.g., as measured by radiographs, magnetic resonance imaging (MRI), or endoscopy) accurately predicts the presence or severity of pain. Central factors alter pain processing by setting the “gain”, such that when peripheral input is present, it is processed against a background of central factors that can enhance or diminish the experience of pain. There are very large inter-individual differences in these central nervous system factors that influence pain perception, such that some individuals with significant peripheral nociceptive input (e.g. from joint damage or inflammation) will feel little or no pain, whereas others are very pain sensitive, and they can experience pain with minimal or no identifiable abnormal peripheral nociceptive input. This emerging knowledge has important implications for pain management in individuals with chronic rheumatologic disorders.