A12-year-old girl presents with complaints of intermittent pain and stiffness involving her hands. this pain has been progressively worsening over the past 3 years. she relates that for the past 2 months she has been feeling increasingly tired and has experienced swelling and stiffness of her hands, which appears worse in the morning and is relieved as the day progresses. the physical examination shows she has a low-grade fever. there are multiple symmetrical joint swelling of the proximal interphalangeal and metacarpophalangeal joints with associated warmth, tenderness, and effusion. initial laboratory findings include a cbc that reveals mild anemia, an elevated erythrocyte sedimentation rate, a positive rheumatoid factor, and a negative antinuclear antibody (ana) test. x-rays of the hands and wrists show soft tissue swelling and periarticular osteopenia. what is your diagnosis?