Synovitis is a medical condition that refers to inflammation of the synovial membrane, which lines joints that possess cavities, known as synovial joints. The condition is usually painful, particularly when the joint is moved, and the joint usually swells. Synovitis may occur in association with arthritis as well as lupus, gout, and other conditions. It is more commonly found in rheumatoid arthritis than in other forms of arthritis, and can thus serve as a distinguishing factor, although it is also present in many joints affected with osteoarthritis. In rheumatoid arthritis, the fibroblast-like synoviocytes, highly specialized mesenchymal cells found in the synovial membrane, play an active and prominent role in the synovitis. Long-term occurrence of synovitis can result in degeneration of the joint.

The symptoms of synovitis include joint tenderness or pain, swelling, and hard lumps called nodules. The joint pain is usually accompanied by warmth and stiffness that’s worse in the morning. The symptoms are often short-lived and may be felt in different parts of the body at different times. However, when synovitis is caused by overuse of a joint, the pain usually remains in one spot.

A rheumatologist will aim to diagnose the cause of the patient’s pain by first determining whether it is inside the joint itself, meaning true synovitis, or if it is actually caused by an inflammation of the tendons, referred to as tendonitis. Imaging, such as an MRI or musculoskeletal ultrasound, is often required to make a firm diagnosis. Treatment for synovitis includes rest, ice, immobilization, and oral nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, and may include steroid injections into the joint. Surgery may be indicated in longstanding cases.