Complex regional pain syndrome, also known as reflex sympathetic dystrophy, refers to a group of painful diseases marked by persistent regional pain that appears to be disproportionate in time or severity to any known trauma or other lesion. Changes in the somatosensory systems, which process noxious, tactile, and temperature information; the sympathetic systems, which innervate skin structures like blood vessels and sweat glands; and the somatomotor systems, which control movement, cause complex regional pain syndrome. The modifications indicate that the central nervous system representations have been updated. Patients with complex regional pain syndrome also have abnormalities in their peripheral nervous system. Pain (spontaneous pain, hyperalgesia, allodynia), active and passive movement disorders (including an increased physiological tremor), abnormal regulation of blood flow and sweating, oedema of skin and subcutaneous tissues, and trophic changes of skin, skin organs, and subcutaneous tissues are the most common symptoms. Inflammation caused by the nerves' release of certain pro inflammatory chemical signals, sensitised nerve receptors that send pain signals to the brain, dysfunction of the local blood vessels' ability to constrict and dilate appropriately, and maladaptive neuroplasticity are all clinical features of the complex regional pain syndrome. The signs and symptoms of the complicated regional pain system usually appear close to the site of the injury.