Rheumatoid arthritis of the hands. Coloured X-ray of a section through the deformed hands of a patient affected by rheumatoid arthritis. Rheumatoid arthritis is a degenerative autoimmune disease that mainly affects the capsule (synovium) around the synovial (flexible) joints, causing chronic inflammation. It can be a debilitating and painful condition and can lead to deformities and loss of functioning and mobility.