Older terms used to describe complex regional pain syndrome are reflex sympathetic dystrophy syndrome and causalgia. Guide to Complex Regional Pain Syndrome Complex regional pain syndrome is a chronic pain condition thought to be a disorder of the nervous system. Repetitive stress injuries include a large group of conditions that primarily affect the soft tissues, including the nerves, tendons, ligaments, and muscles. TMD disorders fall into three main categories: myofascial arthritis joint pain, internal derangement of the joint, and degenerative joint disease, such as osteoarthritis or rheumatoid arthritis in the jaw joint. Guide To Temporomandibular Disorders TMD is not just one disorder, but a group of conditions, often painful, that affect the jaw joint and the muscles that control chewing.