Undifferentiated arthritis is a group of inflammatory arthritis with an unclear diagnosis. In addition to these clearly classified rheumatic diseases, there are still many joint pains with unclear causes and pathogenesis, and the rheumatology community currently refers to this group of diseases as “undifferentiated arthritis”. The diagnosis of undifferentiated arthritis is usually considered when peripheral arthritis is present but does not meet the classification criteria of any other autoimmune disease. Most cases of undifferentiated arthritis begin insidiously, with pain in the wrists, metacarpophalangeal joints, and other joints of the extremities. However, in some cases, the symptoms may be limited to joint swelling and pain, but may also be accompanied by extra-articular manifestations such as fatigue. In addition, it is recommended that patients with undifferentiated arthritis go to the hospital to avoid delay.