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.

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RA and AS can appearTrusted Source similar, but there are differences.

Differences between AS and RA

Here are some differences:

Rheumatoid ArthritisAnkylosing Spondylitis
mainly affects the joints in the arms, legs, fingers, and toesprimarily affects the back
is an autoimmune diseaseit is not yet clearTrusted Source if AS is an autoimmune or autoinflammatory disease, where inflammation results from activity within the body but is not necessarily immune-related
most people with RA have rheumatoid factor (RF) in their bloodblood tests for people with AS are usually nonspecific, but 50% to 70%Trusted Source reveal signs of inflammation
complications of RA include secondary Sjögren disease, which causes dry eyes and mouth•50%Trusted Source of people develop intestinal problems, such as inflammatory bowel disease (IBD)
•25% to 35% have anterior uveitis
•10% develop psoriasis
does not typically involve dactylitis, or “sausage fingers”dactylitis, or “sausage fingers” can occurTrusted Source
affects joints in the knees, hands, and throughout the bodyonly 1 in 3 peopleTrusted Source with AS have peripheral joint involvement
causes rheumatoid nodules, bumps that develop around the affected jointsdoes not involve rheumatoid nodules
risk of RA increases with age, peaking at ages 65 to 80 yearsTrusted Sourceoften appears before the age of 40Trusted Source years, with 80%Trusted Source experiencing symptoms before age 30 years
mostly starts with tenderness and pain in one or more joints, usuallyTrusted Source the small joints in the hands or feetstarts with severe back pain but often has no early symptoms
is more common in femalesmore often affects males
around 40% of peopleTrusted Source with RA will have difficulty working or carrying out daily tasks within 10 years of a diagnosissevere functional loss is rareTrusted Source with AS
tobacco use increases the risk of RArisk factors for AS are unclear, but 70% of people may have intestinal problems before AS appears
around 31.5%Trusted Source of those with RA experience long-term remission from 8 months on average after starting treatmentstudies 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 evidence suggestsTrusted Source the causes are quite different, making it unlikely, but not impossible, that a person will have both.

Learn more about RA and AS.

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 40Trusted Source.
  • 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 includeTrusted Source:

  • 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 increase the riskTrusted Source of the autoimmune diseases IBD and psoriasis, suggesting a possible link. People with RA are also more likelyTrusted Source to develop other autoimmune conditions, such as Sjögren disease.

However, RA and AS rarely occur together, suggesting no link.

Some experts believe AS and RA may shareTrusted Source some underlying factors. However, these factors are unclear.

Doctors sometimes mistake AS for RA if it affects joints other than the vertebrae.

Other conditions that can resembleTrusted Source AS include:

Conditions that can resembleTrusted Source RA include:

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 severely affectTrusted Source a person’s life expectancy, but treatment can help manage disease progression.

Most peopleTrusted Source with AS continue an active life, although pain, discomfort, and some loss of functionality may affect their quality of life. AS can affect life expectancy if a person lives with it for a long time, particularly if cardiovascular issues or other AS complications arise.

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.