Key differences between rheumatoid arthritis and ankylosing spondylitis include the joints they affect and who’s most likely to develop each condition. Some treatment options may also work for one but not the other.

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are among the most common rheumatic (joint) conditions.

RA is an autoimmune disorder that causes joint pain and inflammation. It most commonly affects the joints in your hands, wrists, and knees.

AS is also an autoimmune disorder. It primarily causes pain and inflammation in the joints of your spine.

RA and AS are both types of arthritis, but they’re not the same. Their symptoms and treatment are different. But these conditions can sometimes present in a similar way, making it hard to tell them apart. In the past, doctors sometimes incorrectly diagnosed AS as RA.

Read this article to learn about the similarities and differences between RA and AS, including their diagnoses and the symptoms, treatments, and outlooks for people who have them.

RA usually affects the joints in your:

  • hands
  • wrists
  • knees

It can also affect other joints, including in your:

A hallmark of RA is symmetrical involvement. That means it usually affects joints in both extremities. For example, it would affect both of your wrists or both knees.

Unlike AS, RA doesn’t usually affect the joints of your spine. One exception is your cervical spine, the neck region of your spine.

AS mainly affects the joints of your spine. It can also cause inflammation in your joints, such as in your:

When AS affects nonspine joints, it’s usually symmetrical, but there can be exceptions.

Common symptoms of RA and AS include:

Unique symptoms of RA include:

  • pain, stiffness, tenderness, and swelling in joints of your extremities
  • symptoms in more than one joint
  • symptoms that begin in smaller joints (for example, your fingers or toes)

Unique symptoms of AS, on the other hand, include:

  • severe back pain
  • poor posture or stooped shoulders
  • pain, stiffness, tenderness, or swelling that affects large joints outside of your spine

RA and AS occur in around 0.3% to 1.5% of all people. You might inherit either condition due to a group of genes called human leukocyte antigens (HLAs).

RA is more common in people assigned female at birth, while AS is more common in people assigned male at birth. AS usually begins before 30 years of age. RA typically happens later, between 40 and 50 years of age.

Other risk factors for RA include:

  • smoking and secondhand smoke exposure, especially in childhood
  • obesity
  • history of giving birth (with people assigned female at birth who’ve never given birth being at a greater risk of RA)

Other risk factors for AS include:

  • gut inflammation
  • childhood infections

Diagnosing both RA and AS can be a lengthy process, requiring multiple labs and imaging tests. This is because these conditions can have overlapping symptoms with other joint disorders, and no single test can identify either AS or RA.

The first step in diagnosing either condition is a physical exam. A doctor will ask about your symptoms, medical and family history, and risk factors. They’ll check your joints for swelling, tenderness, and range of motion.

Next, they’ll order imaging and blood tests.

Imaging tests doctors use to diagnose RA and AS include:

  • X-rays: X-rays help a doctor to assess the extent of inflammation in your affected joints and bones.
  • MRI: Doctors use MRI for a more detailed look inside your affected joints.
  • Ultrasound: Ultrasounds create a “map” of affected bones, joints, and tendons.

Blood tests include:

  • Complete blood count (CBC): A CBC helps to confirm or rule out blood conditions (for example, anemia) commonly associated with certain joint disorders.
  • Erythrocyte sedimentation rate (ESR) test: An ESR test can help identify the extent of inflammation in your blood.
  • C-reactive protein (CRP) test: A CRP test measures your inflammation.
  • Antinuclear antibody (ANA) test: An ANA test looks for evidence of an autoimmune condition.
  • Rheumatoid factor test: A rheumatoid factor test can help distinguish RA from other conditions.
  • HLA-B27 test: An HLA-B27 test can detect a genetic marker common in AS.

Related conditions

RA and AS are often associated with other (nonjoint) conditions. This is because a faulty immune system can mistakenly attack multiple organs and tissues.

Common conditions seen in people with RA and AS include:

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Treatment of RA and AS is similar overall, but there are some key differences. Rheumatologists — doctors who treat joint conditions — use a treatment strategy called “treat-to-target (T2T)” when managing both RA and AS. T2T involves setting a treatment target and following a strict monitoring protocol with necessary adjustments to reach the target.

Doctors use the following medications for RA and AS:

Nonpharmacological treatment for RA and AS includes the following:

It’s difficult to estimate the outlook for people with either RA or AS because it depends on many factors.

While neither RA nor AS are fatal, complications can shorten your life span by 10 to 15 years. But with newly available treatments over the last few decades, many people with these conditions live past 80 or even 90 years of age.

Living with RA or AS can significantly affect your quality of life, mental health, and emotional well-being. Be sure to let a doctor know if you have any difficulties dealing with your condition. They’ll be able to help you.

Can a person have both RA and AS?

It’s pretty rare for people to have both RA and AS at the same time. This is because these conditions have different mechanisms of development.

Still, it’s not impossible. A 2021 Chinese study observed 22 people with both RA and AS in a span of 6 years.

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Here’s a quick summary of the key similarities and differences between RA and AS.

Rheumatoid arthritisAnkylosing spondylitis
Who gets it?• more common in people assigned female at birth
• usually begins after 40
• more common in people assigned male at birth
• usually begins before 30
Symptoms• pain/swelling in joints of your extremities
• begins in smaller joints
• severe back pain
• pain/swelling in large joints outside of your spine
Diagnosis• physical exam
• imaging
• blood tests, including rheumatoid factor test
• physical exam
• imaging
• blood tests, including the HLA-B27 test
Treatment• NSAIDs and corticosteroids for pain
• biologics
• JAK inhibitors
• NSAIDs and corticosteroids for pain
• biologics
• JAK inhibitors
Outlook• not fatal but may affect life expectancy• not fatal but may affect life expectancy

RA and AS are different types of arthritis. Although related, they have different symptoms and causes. These conditions do have many similarities, which can complicate diagnosing them.

Treatment of RA and AS is similar, but there are key differences. Neither is fatal, but some people may develop complications that can shorten their life span.