[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Bones, joints and soft tissue](https://durgical.com/en/general-pathology/areas/bone-soft/) › Rheumatoid arthritis: synovitis and pannus

# Rheumatoid arthritis: synovitis and pannus

- Lesion

In rheumatoid arthritis the immune system inflames the joint lining, which grows into a destructive pannus that erodes cartilage and bone.

Updated Nov 12, 2026

## Key points

- Women about three times more than men; peak in the fourth to sixth decades.
- Symmetric polyarthritis of hand and foot small joints (MCP, PIP, wrists), sparing the DIP joints; morning stiffness over an hour.
- Anti-CCP (anti-citrullinated peptide) antibodies are the most specific test; rheumatoid factor is IgM against the Fc of IgG.
- Pannus: proliferating synovium with inflammatory cells and granulation tissue that erodes cartilage and bone; later fibrous then bony ankylosis.
- Deformities: ulnar deviation, swan neck, boutonnière; atlantoaxial subluxation.
- Extra-articular: rheumatoid nodules, interstitial lung disease, vasculitis, pericarditis, scleritis, anaemia of inflammation, secondary AA amyloidosis, Felty syndrome.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Osteoarthritis vs rheumatoid arthritis
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes
- In the lab

- Study Test yourself

- Connections Connections

## What it is

Rheumatoid arthritis is a chronic systemic autoimmune disease that mainly attacks the synovium of small and large joints symmetrically. In genetically susceptible people (HLA-DRB1 'shared epitope', PTPN22), environmental factors such as smoking promote citrullination of proteins, and loss of tolerance produces anti-citrullinated protein antibodies and rheumatoid factor. CD4 Th1 and Th17 cells, B cells, macrophages and synovial fibroblasts sustain inflammation through TNF, IL-6 and IL-17, and the hyperplastic synovium (pannus) destroys cartilage and bone. It also affects skin, lungs, vessels, heart and eyes.

## Structure

- Synovium: villous hyperplasia of lining cells, dense perivascular lymphocytes and plasma cells (sometimes lymphoid follicles), new vessels and fibrin.
- Pannus spreads over and under the cartilage from the joint margin, eroding cartilage and juxta-articular bone.
- Neutrophils and fibrin in synovial fluid; periarticular osteopenia on X-ray.
- Rheumatoid nodule: central fibrinoid necrosis surrounded by palisading macrophages and granulation tissue, in skin over pressure points (forearm extensor surface) or in lungs.
- Rheumatoid vasculitis can affect small and medium vessels.

## Step by step

- Genetic risk (HLA-DRB1 shared epitope, PTPN22) meets triggers such as smoking and periodontal bacteria that citrullinate proteins.
- Citrullinated peptides bind HLA-DR and activate CD4 T cells, which help B cells make anti-CCP and rheumatoid factor, years before symptoms.
- Th1 and Th17 cells, macrophages and immune complexes inflame the synovium; TNF, IL-1, IL-6 and IL-17 rise.
- Synovial fibroblasts become invasive and, with RANKL from T cells, recruit osteoclasts that erode bone.
- Pannus destroys cartilage; the joint becomes deformed and may fuse.

## Osteoarthritis vs rheumatoid arthritis

| Feature | Osteoarthritis | Rheumatoid arthritis |
| --- | --- | --- |
| Primary problem | Cartilage degeneration | Autoimmune synovitis |
| Joints | Weight-bearing joints, DIP and PIP, first CMC; asymmetric | MCP, PIP, wrists, feet; symmetric; DIP spared |
| Morning stiffness | Short (under 30 minutes) | Long (over an hour) |
| Synovium | Mild inflammation | Pannus with lymphocytes and plasma cells |
| Bone changes | Osteophytes, sclerosis, subchondral cysts | Marginal erosions, periarticular osteopenia, ankylosis |
| Labs and systemic disease | Normal labs; none | Anti-CCP, RF, high ESR and CRP; nodules, lung, vessels, anaemia |

## Clinical notes

- Treatment aims at early disease control with disease-modifying drugs (methotrexate) and biologics against TNF, IL-6, B cells or T-cell co-stimulation.
- Cardiovascular disease is the main cause of excess death.
- In Latin America, rheumatoid arthritis is common and access to biologics varies; early referral prevents deformity.

## In the lab

- Anti-CCP antibodies: high specificity; rheumatoid factor: sensitive but less specific.
- Synovial fluid: inflammatory, with many neutrophils and low viscosity.

## Memory aid

RA is the synovium gone rogue: citrulline wakes it, T cells feed it, pannus eats the joint.

## Test yourself

Think of the answer, then tap the question to see it.

## What is pannus?

Proliferating inflamed synovium with granulation tissue that grows over cartilage and erodes cartilage and bone.

## Which antibody test is most specific for rheumatoid arthritis?

Anti-citrullinated protein (anti-CCP) antibodies.

## Which finger joints are typically spared in rheumatoid arthritis?

The distal interphalangeal joints.

## What is a rheumatoid nodule under the microscope?

Central fibrinoid necrosis surrounded by palisading macrophages and granulation tissue.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/general-pathology/rheumatoid-arthritis-synovitis-and-pannus/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/)
- [HLA associations with disease](https://durgical.com/en/immunology/hla-associations-with-disease/)
- [TNF-α](https://durgical.com/en/immunology/tnf/)
- [Interleukin-17](https://durgical.com/en/immunology/interleukin-17/)
- [Type III hypersensitivity (immune complexes)](https://durgical.com/en/immunology/type-iii-hypersensitivity/)
- [Synovial joints: capsule, synovial membrane and articular cartilage](https://durgical.com/en/histology/synovial-joints-capsule-synovial-membrane-and-articular-cartilage/)

## Connections

## Related 5

- [Osteoarthritis](https://durgical.com/en/general-pathology/osteoarthritis/)
- [Juvenile idiopathic arthritis](https://durgical.com/en/general-pathology/juvenile-idiopathic-arthritis/)
- [The lung in autoimmune disease](https://durgical.com/en/general-pathology/the-lung-in-autoimmune-disease/)
- [Anaemia of chronic inflammation: IL-6, hepcidin and locked-away iron](https://durgical.com/en/general-pathology/anaemia-of-chronic-inflammation-il-6-hepcidin-and-locked-away-iron/)
- [Restrictive cardiomyopathy and cardiac amyloidosis](https://durgical.com/en/general-pathology/restrictive-cardiomyopathy-and-cardiac-amyloidosis/)

## Related conditions 5

- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- [Rheumatoid arthritis of the hand and wrist](https://durgical.com/en/conditions/rheumatoid-arthritis-of-the-hand-and-wrist/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Amyloidosis](https://durgical.com/en/conditions/amyloidosis/)
- [Sjögren disease](https://durgical.com/en/conditions/sjogren-disease/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Rheumatoid Arthritis](https://www.ncbi.nlm.nih.gov/books/NBK441999/) (StatPearls (NCBI Bookshelf), 2025); [Burden of illness of rheumatoid arthritis in Latin America: a regional perspective](https://europepmc.org/article/PMC/PMC4617840/) (Clinical rheumatology, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/rheumatoid-arthritis-synovitis-and-pannus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/rheumatoid-arthritis-synovitis-and-pannus/