What is synovitis?

In a way, it's a fancy term for "arthritis," which means joint inflammation.

But there is a difference between synovitis and arthritis. Synovitis describes prominent joint inflammation in which the most dramatic inflammation is of the synovium. This is a thin layer of cells that lines our joints.

Some types of arthritis, such as osteoarthritis, cause little if any synovial inflammation. This is quite different from the marked synovial inflammation seen in rheumatoid arthritis.

Doctors may suspect synovitis after hearing details of a person's joint pain. For example, synovitis tends to cause:

• swelling
• limited motion
• stiffness that is worse in the morning

A physical exam is often helpful to confirm synovitis. For example, a doctor may diagnose synovitis in a finger joint if there is swelling, warmth, soreness when touched, and a thickening of the joint that feels "spongy."

For a deep joint, such as the hip, synovitis cannot be diagnosed by a physical exam alone. Making this diagnosis may require an MRI or even a biopsy of the joint.

The difference between synovitis and joint disease that is non-inflammatory is important. Joint diseases in which synovitis is a dominant feature are treated differently from joint disease with less synovial inflammation.

For example, if an infection is not involved, drugs that suppress the immune system are used to treat chronic synovitis. But these drugs usually don't work when there is no synovitis.

Because there are more than 100 types of arthritis, the presence or absence of significant synovitis is an important way to classify these diseases and to guide treatment.