Clinical meaning
Chronic pain is defined as pain persisting beyond the expected healing time, typically > 3 months, and represents a distinct disease process rather than merely prolonged acute pain. Central sensitization occurs when persistent nociceptive input from peripheral tissues causes functional and structural changes in the central nervous system, including increased excitability of dorsal horn neurons, reduced descending inhibition, and expansion of receptive fields. This results in amplified pain processing where the nervous system maintains a pain state even after the original tissue injury has healed. Common chronic pain syndromes include fibromyalgia (widespread musculoskeletal pain with central sensitization), chronic low back pain, chronic headache disorders, complex regional pain syndrome (CRPS), and myofascial pain syndrome. Psychosocial factors significantly influence chronic pain through the biopsychosocial model: biological (tissue damage, genetics), psychological (depression, anxiety, catastrophizing, fear-avoidance), and social (disability, isolation, financial stress) dimensions all contribute. Chronic pain management requires a multidisciplinary approach addressing all three dimensions.