Typical joint manifestations of rheumatoid arthritis (1) Morning stiffness lasting 1 hour is diagnostic of rheumatoid arthritis (RA). (2) Pain and swelling in multiple joints, small joints, and symmetrical joints, especially in the proximal interphalangeal joints, metacarpophalangeal joints, and wrist joints. The phenomenon of “trigger finger” or “hinge-unlocking” may occur, as well as cystic sensation around the small joints due to synovial thickening, and swelling and pressure pain in the soft tissues on the extensor side of the wrist joint. (3) Joint deformities include pike swelling, ulnar deviation deformity, proximal interphalangeal joint palmar subluxation, crest and valley deformity, ulnar subluxation, buttonhole flower and swan neck deformity, claw-shaped hand, telescope hand, crossed toe deformity, heel valgus deformity, etc. (4) Osteoporosis. Pathological osteoporosis is commonly found in joints eroded by lesions. Common clinical tests associated with rheumatoid arthritis (1) Rheumatoid factor: (See: I. What is rheumatoid factor? What are its clinical implications?) (2) Sedimentation (ESR): clinical significance of increased sedimentation Physiologically increased sedimentation varies with age and gender, generally higher in women than in men, and in some women during menstruation, and from the third trimester of pregnancy to one month after delivery; it also increases in young children. Most rheumatic diseases may increase during the inflammatory phase, such as systemic lupus erythematosus, rheumatic fever, rheumatoid arthritis, ankylosing spondylitis, dry syndrome, dermatomyositis, vasculitis, nodular disease, etc. When the disease improves and remits, it will drop significantly or return to normal. However, increased sedimentation is not unique to rheumatoid arthritis and cannot be used as a specific diagnostic indicator. Increased sedimentation can occur in other acute inflammatory diseases, such as active tuberculosis, anemia, malignant tumors, heavy metal poisoning, etc. (3) C-reactive protein (CRP): CRP is a glycoprotein in the serum of certain diseases, which is an acute reactive phase substance, and its elevation can be seen in various diseases such as acute septic inflammation, tissue necrosis, malignant tumor and rheumatic diseases. It is important for the diagnosis of inflammatory activity in rheumatoid arthritis. (4) Anti-cycloguanine polypeptide antibody (CCP) Anti-cycloguanine polypeptide antibody (CCP) is a newly discovered antibody with high diagnostic significance for rheumatoid arthritis. It has a specificity of 96% and a sensitivity of 76%. Its specificity is significantly higher than that of rheumatoid factor (RF) and can be used for the early diagnosis of rheumatoid arthritis. (5) Anti-keratin antibody (AKA) Anti-keratin antibody (AKA) is related to the activity and severity of rheumatoid arthritis, and often appears early in the disease or even when clinical symptoms are not obvious. Follow-up of those who are positive for antibodies reveals that more often become classic rheumatoid arthritis. Therefore, anti-keratin antibodies are important for the diagnosis and prognosis of rheumatoid arthritis, with a sensitivity of 33% and a specificity of 87% – 95% for the diagnosis of rheumatoid arthritis. (6) Anti-RA33/RA36 RA33 antibody can be found in early rheumatoid arthritis and is beneficial for early diagnosis. RA36 antibody is only found in rheumatoid arthritis and has a high specificity. Therefore, the combination of the two tests is meaningful for the differential diagnosis of rheumatoid arthritis.