Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) rheumatoid arthritis ?
    ### Response:
    Rheumatoid arthritis is a disease that causes chronic abnormal inflammation, primarily affecting the joints. The most common signs and symptoms are pain, swelling, and stiffness of the joints. Small joints in the hands and feet are involved most often, although larger joints (such as the shoulders, hips, and knees) may become involved later in the disease.
    