Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are long-term inflammatory diseases. Both cause joint damage that worsens with time.
RA is an autoimmune disease that involves joint inflammation and other symptoms such as dry eyes and interstitial lung disease. An autoimmune disease happens when the immune system mistakenly attacks healthy tissues, causing inflammation and damage.
AS mainly affects joints in the axial spine, which includes the bones and joints of the back, head, neck, and ribs. AS involves arthritis-like symptoms but can also lead to inflammatory bowel disease and uveitis.
Experts have not yet confirmed whether AS is an autoimmune disease, but some evidence suggests it may be.
RA and AS
Differences between AS and RA
Here are some differences:
| Rheumatoid Arthritis | Ankylosing Spondylitis |
|---|---|
| mainly affects the joints in the arms, legs, fingers, and toes | primarily affects the back |
| is an autoimmune disease | it is |
| most people with RA have rheumatoid factor (RF) in their blood | blood tests for people with AS are usually nonspecific, but |
| complications of RA include secondary Sjögren disease, which causes dry eyes and mouth | • •25% to 35% have anterior uveitis •10% develop psoriasis |
| does not typically involve dactylitis, or “sausage fingers” | dactylitis, or “sausage fingers” |
| affects joints in the knees, hands, and throughout the body | only |
| causes rheumatoid nodules, bumps that develop around the affected joints | does not involve rheumatoid nodules |
| risk of RA increases with age, peaking at ages | often appears before the |
| mostly starts with tenderness and pain in one or more joints, | starts with severe back pain but often has no early symptoms |
| is more common in females | more often affects males |
| around | severe functional loss |
| tobacco use increases the risk of RA | risk factors for AS are unclear, but 70% of people may have intestinal problems before AS appears |
| around | studies suggest an average of 25% of people with AS are in long-term remission 5 years after diagnosis |
Similarities between AS and RA
Some similarities include:
- They are both chronic (long term) inflammatory diseases.
- They both affect the joints.
- Both can run in families.
- Both are likely occur when a person with certain genetic features is exposed to certain environmental factors.
- Both involve flares and remission but continue to worsen over time.
- The rate of progression varies between individuals in both diseases.
- Both RA and AS increase the risk of lung and cardiovascular disease and eye problems.
Scientists are still exploring why RA and AS occur. Current
RA and AS share some symptoms but not all.
Ankylosing spondylitis symptoms
A doctor may suspect AS if a person has back pain plus at least four of the following:
- Symptoms starting
before age 40 . - It begins gradually but insidiously, meaning it causes damage even while symptoms are mild.
- Exercise reduces pain.
- Rest does not improve symptoms.
- Pain and stiffness are worse in the morning and ease with movement.
In time, spinal fusion can result, where the vertebrae grow together, making them inflexible.
Learn about the stages of AS.
Rheumatoid arthritis symptoms
Common symptoms of RA
- joint pain, tenderness, and swelling that develop over a few weeks to a few months
- joint stiffness, especially in the morning
- a “boggy” feeling on touching the tissues around the joint, it may feel mushy with a soft quality to it
- reduced range of motion in the joints
- weak grip in the hands
- rheumatoid nodules
- joint deformities as RA progresses
- complications such as heart, lung, and eye problems or dry eyes and dry mouth
RA does not involve the lower back, although it can affect the area around the neck.
Learn about the stages of RA.
It is rare for AS and RA to occur together, but some people have both.
The authors of a 2022 study note that there are only 81 recorded cases, but there could be more. They also cite a 2017 study that looked at 286,601 people with RA and found that 1.16% also had AS.
Experts consider RA and AS to be separate diseases.
The affected joints, age groups, and development are all different. Blood and imaging tests produce different results.
AS appears to
However, RA and AS rarely occur together, suggesting no link.
Some experts believe AS and RA
Doctors sometimes mistake AS for RA if it affects joints other than the vertebrae.
Other conditions that
- mechanical low back pain, for instance, due to an injury
- lumbar spinal stenosis
- diffuse idiopathic skeletal hyperostosis
Conditions that
- osteoarthritis
- psoriatic arthritis
- systemic lupus erythematosus (lupus or SLE)
- Sjögren disease
- polymyalgia rheumatica
- gout
- calcium phosphate deposition disease, or pseudogout
Both AS and RA are long-term conditions that worsen over time. They both involve flares and remissions. During a flare, symptoms can be severe. During remission, they may be mild or disappear.
In both cases, the outlook can vary widely depending on factors such as:
- severity
- access and response to treatment
- current age and age at onset
- complications
- body weight
- lifestyle factors, such as exercise and diet
In the later stages of RA, a person may have difficulty moving or doing daily tasks, but not everyone reaches this stage. They may also develop potentially life threatening complications, such as cardiovascular disease. RA can
Learn more about the outlook for RA and the outlook for AS.
Rheumatoid arthritis resources
Visit our dedicated hub for more research-backed information and in-depth resources on rheumatoid arthritis.
AS and RA are both long-term inflammatory diseases, but they have different causes and symptoms. AS primarily affects the back, while RA causes joint pain and swelling. So far, there is no evidence of a link between them.
Treatment can help manage both conditions and prevent complications.