Ankylosing spondylitis primarily affects the spine, but peripheral joints can also be involved. In the past, the disease was thought to be a variant of rheumatoid arthritis, called central or rheumatoid spondylitis. It is now known to be completely different from rheumatoid arthritis and is a separate disease. It is characterized by: (1) mostly male patients; (2) the age of onset is mostly 15-30 years old; (3) it is genetically related, with multiple patients in the same family, and HLA-B27 is 90% to 95% positive; (4) serum rheumatoid factor is mostly negative, and rheumatoid nodules are rare; (5) it mainly invades the sacroiliac joints and spine, which easily leads to bony joint ankylosis, intervertebral ligament calcification, and bamboo-like changes in spine radiographs; (6) Hand and foot joints are rarely involved; (7) pathological changes are tendonitis at the attachment point of the bone attachment of the joint capsule; (8) if there are lesions in the joints of the extremities, more than half of the patients are asymmetric; (9) conjunctivitis and uveitis may be combined. Rheumatoid arthritis is characterized by symmetrical swelling and pain of multiple joints, accompanied by morning stiffness of the joints. At the beginning, the disease often starts with generalized fatigue, loss of appetite, emaciation, numbness and tingling in the hands and feet, followed by pain and stiffness in one or two joints, especially morning stiffness, which can last for several hours, but the appearance of the joints is not abnormal. Some patients may develop fever and other symptoms.