How Pannus Develops With Arthritis

In This Article

Pannus is a complication of late-stage osteoarthritis (OA) and rheumatoid arthritis (RA). It occurs when a layer of fibrous tissue grows over the surface of a normal structure in your body. In OA and RA, it's an overgrowth of joint lining (synovium) that invades the space between the bones inside a joint and covers the bones and the protective layer of articular cartilage.

This can cause erosions on the bone, invade the bone and bone marrow, and destroy surrounding structures including the joint capsules and tendons. All of this can cause inflammation and pain that only adds to the effects of an already painful condition. The process is generally less destructive in OA than in RA.

Pannus has become less common as medical science has made advances in diagnosis and treatment, which often prevent OA and RA from progressing into the later stages.

Why Pannus Forms

Osteoarthritis and rheumatoid arthritis damage your joints via different mechanisms, but they do have certain things in common. Both diseases involve certain proteins from the immune system called cytokines, which help regulate inflammation. Researchers theorize that cytokines start a cycle that ends with pannus.

First, the abundance of cytokines causes the blood vessels in the synovium to multiply, which is called hypervascularization. That leads to an increase in blood flow to the area and excessive cell reproduction, which causes synovial thickening. The joint doesn't have enough space to accommodate the excess tissue, so the synovium infiltrates all of the small spaces, covering the structures that surround it.

Research suggests that other immune cells, including interleukin 1beta (IL-1b) and tumor necrosis factor-alpha (TNF-a), may also be involved in pannus.

The word pannus comes from the Latin word for garment or cloth. Medically speaking, it's any abnormal tissue that covers a normal structure and contains blood vessels.

Pannus in OA vs. RA

So far, very little research has been done about how pannus may differ in osteoarthritis versus rheumatoid arthritis. According to a study published in 2019 that directly compared pannus tissues removed from people with both diseases, the samples looked nearly indistinguishable under a microscope.

However, the pannus of OA featured:

  • Less overgrowth of synovial tissues
  • Less fibrous tissue
  • Less inflammation of cells from the immune system
  • Slightly fewer extra blood vessels

These factors likely explain why pannus tends to be less destructive in OA. This may be due to autoimmunity, a complicated immune system dysfunction that characterizes RA but not OA.

Symptoms and Complications

The symptoms caused by pannus are similar to those of OA and RA, with the primary ones being joint pain and inflammation. These result from the destruction of bone and cartilage in the joint.

However, the thickened synovial tissue also contributes to a buildup of excess synovial fluid, which can increase pain and swelling. Proteins in this fluid can cause further damage to joint structures.

If it goes untreated, pannus can lead to not only severe pain, but lost mobility and permanent deformity.

Pannus can also form in places other than the joints, including over the cornea or on a prosthetic heart valve (and produce related symptoms like vision loss as a result). As pannus grows, it may appear tumor-like.

Diagnosis

If your doctor suspects pannus based based on your symptoms, they can order imaging, including an X-ray, ultrasound, magnetic resonance imaging (MRI) scan, or a computed tomography (CT) scan to check for it.

To help your doctor figure out what's causing your symptoms, try to provide details about how you feel such as:

  • How long you've had that particular pain
  • Whether the pain has worsened recently
  • Whether pain is occurring symmetrically (in the same joint on both sides of your body)

Treatment

The fact that you've developed pannus may indicate that your current medication isn't controlling your disease enough, so your doctor may want to switch you to a different drug or add a new one to your regimen.

Drug classes frequently used for cases involving pannus include:

Some research shows the involvement of Janus kinase enzymes in the formation of RA pannus, which could mean that the newer class of drugs called Janus-kinase (JAK) inhibitors could be used to treat pannus in the future.

In more serious cases, or if your pannus doesn't respond to treatment, surgical removal may be an option.

A Word From Verywell

If your arthritis is well treated, you're unlikely to ever develop this complication. Taking your medication, keeping follow-up appointments, and letting your doctor know about any changes in your symptoms can help you manage your disease well, and maintain a good quality of life, in the long term.

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  2. Cajas LJ, Casallas A, Medina YF, Quintana G, Rondon F. Pannus and rheumatoid arthrits: Historic and pathophysiological evolution. Apr 2019;26(2):118-128. doi:10.1016/j.rcreue.2018.10.005

  3. Yang CC, Lin CY, Wang HS, Lyu SR. Matrix metalloproteases and tissue inhibitors of metalloproteinases in medial plica and pannus-like tissue contribute to knee osteoarthritis progressionPLoS One. 2013;8(11):e79662. Published 2013 Nov 4. doi:10.1371/journal.pone.0079662

  4. Veale DJ, Orr C, Fearon U. Cellular and molecular perspectives in rheumatoid arthritisSemin Immunopathol. 2017;39(4):343-354. doi:10.1007/s00281-017-0633-1

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