Differential diagnosis Many disorders can simulate rheumatoid arthritis: Crystal-induced arthritis Systemic lupus erythematosus (SLE) Sarcoidosis (rarely causes a polyarticular arthritis) Reactive arthritis Psoriatic arthritis Ankylosing spondylitis Infectious causes such as hepatitis C, parvovirus B19, alpha virus, Lyme disease, and Whipple disease Osteoarthritis Some patients with crystal-induced arthritis, especially calcium pyrophosphate arthritis, may meet criteria for rheumatoid arthritis; however, synovial fluid examination should clarify the diagnosis.