Reactive arthritis and ankylosing spondylitis are both part of a group of conditions called spondyloarthritis (SpA), which mainly affects the joints and spine. For many people, reactive arthritis is a temporary condition. However, reactive arthritis can sometimes progress to a different type of SpA, such as ankylosing spondylitis.

In this article, we’ll explore how these two conditions are similar and how they differ. We’ll also explain how ankylosing spondylitis can sometimes develop in people who start out with reactive arthritis.

What Is Reactive Arthritis?

Reactive arthritis is a rare kind of joint inflammation that happens after your body fights off a bacterial infection, usually in the gastrointestinal (digestive) or genitourinary (urinary) tract. This kind of arthritis often causes swelling and pain in the knees, ankles, or other large joints in the legs, but it can show up in other joints too. Reactive arthritis is usually asymmetrical, affecting one side of the body more than the other. For most people, reactive arthritis goes away on its own in about three to 12 months.

You might hear this condition referred to by its abbreviation (ReA) or as Reiter’s syndrome, which are older names for reactive arthritis.

What Is Ankylosing Spondylitis?

Ankylosing spondylitis, a type of SpA that mainly affects the spine, is considered a more severe type of axial spondyloarthritis. “Axial” means it affects the central part of your body, like your neck, chest, spine, and sacroiliac joints (where the spine connects to the pelvis). Over time, other joints outside the spine, like your hips or shoulders, might also be affected.

In ankylosing spondylitis, the immune system mistakenly causes inflammation in the joints of the spine. Ankylosing spondylitis is a type of chronic arthritis, meaning you have this condition for life.

Causes

Both reactive arthritis and ankylosing spondylitis are associated with a genetic mutation (change) in a gene called human leukocyte antigen-B27 (HLA-B27). This gene helps your immune system recognize the difference between your own cells and foreign invaders, such as bacteria or viruses. Having a certain version of this gene increases your risk of developing a form of spondyloarthritis.

However, not everyone with a mutated copy of HLA-B27 ends up with spondyloarthritis. Researchers believe that SpA must be triggered by a factor such as:

• Certain infections
• Exposure to toxins
• Cigarette smoke
• Alcohol use

Reactive Arthritis Triggers

Certain types of bacterial infections can lead to reactive arthritis. The most common bacterial trigger is Chlamydia trachomatis (chlamydia), a sexually transmitted infection that spreads through sexual contact.

Reactive arthritis can also develop after a gastrointestinal infection caused by bacteria such as:

• Salmonella
• Shigella
• Yersinia
• Campylobacter

These bacteria can cause illness if you eat contaminated food, don’t handle prepared food properly, or come in contact with an infected person’s feces (poop). However, not everyone with an infection caused by one of these bacteria will get reactive arthritis. You’re more likely to develop reactive arthritis if you have an HLA-B27 mutation. Additional risk factors include:

• Being male
• Being under 40 years old
• Having human immunodeficiency virus (HIV)
• Living with another autoimmune disease

Ankylosing Spondylitis Triggers

Researchers don’t know the exact cause of ankylosing spondylitis. Genetics are thought to play an important role. According to the Spondylitis Association of America, more than 95 percent of Caucasian people diagnosed with ankylosing spondylitis have a specific version of the HLA-B27 gene.

Researchers believe that an imbalance in gut bacteria may allow some harmful bacteria to leak into the blood. The immune system may then become confused and trigger inflammation that leads to ankylosing spondylitis in people who are already at risk.

Symptoms

Both reactive arthritis and ankylosing spondylitis can cause joint pain and stiffness. In the early stages, people with reactive arthritis may have some symptoms that usually don’t show up in ankylosing spondylitis. But if reactive arthritis doesn’t go away, symptoms can begin to look more like ankylosing spondylitis.

Reactive Arthritis Symptoms

Symptoms of reactive arthritis may begin a few days or weeks after exposure to bacteria linked to the condition. The symptoms can come and go and range from mild to severe. Most people start to feel better within about three to 12 months.

Joint pain, swelling, and stiffness most often affect the knees, feet, and ankles and sometimes the lower back. Over time, many people with reactive arthritis develop sacroiliitis (inflammation in the sacroiliac joints).

People with reactive arthritis often have symptoms that affect the urinary tract and the eyes. In the urinary tract, reactive arthritis can cause urethritis (inflammation of the urethra — the tube that allows urine to leave the body). In the eyes, inflammation from reactive arthritis can cause:

• Conjunctivitis — Affects the lining of the eyelid
• Uveitis — Affects the inside of the eye
• Iritis — Affects the iris (the colored part of the eye)

Conjunctivitis causes red, itchy eyes, while uveitis and iritis can make eyes painful, swollen, and sensitive to light.

Other symptoms of reactive arthritis include:

• Diarrhea
• Rash
• Mouth ulcers (sores)
• Heel pain
• Fever
• Fatigue (constant tiredness that doesn’t improve with rest)

Ankylosing Spondylitis Symptoms

The symptoms of ankylosing spondylitis usually start between ages 17 and 45. Most people first notice pain and stiffness in their lower back and buttocks due to sacroiliitis. Over time, the joint involvement can spread to the neck, shoulders, hips, and feet.

Ankylosing spondylitis symptoms that affect other parts of the body are similar to those of reactive arthritis. About one-third of people with ankylosing spondylitis develop uveitis or iritis. Other shared symptoms include fatigue, diarrhea, and rash.

Diagnosis

Reactive arthritis and ankylosing spondylitis are typically diagnosed by a rheumatologist — a doctor who specializes in inflammatory conditions of the joints, muscles, tendons, and bones. These conditions can be tricky to diagnose because symptoms vary from person to person.

To make a diagnosis, a rheumatologist will look at your medical history, do a physical exam, and order tests. If you’ve had a recent gastrointestinal or sexually transmitted infection, that could point to reactive arthritis. To check for infections linked to reactive arthritis, your healthcare provider might order tests such as:

• A throat, urine, or cervical culture (swab), depending on the infection
• Urinalysis (urine tests)
• Stool tests
• Joint aspiration (removing synovial fluid from a swollen joint with a needle to check for signs of inflammation)

Imaging tests, such as X-rays, can help look for signs of arthritis. For example, people with ankylosing spondylitis may have erosions (bone damage) on the sacroiliac joints.

No single blood test can specifically check for reactive arthritis or ankylosing spondylitis, but an HLA-B27 test may help identify who’s at risk. Other blood tests can look for signs of inflammation and help rule out other causes.

Treatment

Your treatment plan depends on your symptoms and how much they’re affecting your life. For both reactive arthritis and ankylosing spondylitis, the first step is usually a nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen or naproxen. These medications can help reduce joint pain and inflammation.

If NSAIDs aren’t enough, your doctor may recommend other medications. For example:

• Corticosteroid (steroid) injections can be used to reduce pain and swelling in joints with severe inflammation. These drugs usually provide quick but temporary relief.
• Disease-modifying antirheumatic drugs (DMARDs) may help reduce ankylosing spondylitis symptoms that affect peripheral joints (outside the spine). Researchers are studying whether one type of DMARD, called sulfasalazine (Azulfidine), can also help people with reactive arthritis.
• Biologic medications can reduce inflammation and may help slow disease progression. These advanced treatments are often used for ankylosing spondylitis if other treatments aren’t working well.

People with reactive arthritis may also benefit from antibiotics, especially if the infection that triggered the arthritis is still present. In some cases, long-term antibiotic treatment may help.

Nondrug treatments to help manage symptoms in people with either type of arthritis include:

• Physical therapy to keep joints flexible and strong
• Hot or cold therapy to soothe pain and stiffness
• Regular exercise to stay active and mobile
• Stress management to support mental and emotional health

Your healthcare team can help you understand the best treatment options for you.

How Often Does Reactive Arthritis Progress to Ankylosing Spondylitis?

Most people make a full recovery from reactive arthritis. However, the symptoms can come back for about 15 percent to 20 percent of people and may become a chronic (long-term) form of arthritis. While most people with chronic reactive arthritis have mild symptoms, some individuals may develop ankylosing spondylitis.

One MySpondylitisTeam member shared, “My arthritis started as reactive arthritis. It finally settled into ankylosing spondylitis about nine months later. My rheumatologist did an HLA-B27 test, and I was positive.”

In a 2018 study, about half of participants who didn’t fully recover from reactive arthritis went on to develop chronic arthritis. Of those, around 3.5 percent developed ankylosing spondylitis within two years.

A 2015 study found that people with reactive arthritis may be more likely to progress to ankylosing spondylitis if they:

• Experience lower back pain from sacroiliitis when their symptoms begin
• Have eye inflammation, such as uveitis
• Develop reactive arthritis from a chlamydia infection

If you’ve been diagnosed with reactive arthritis, talk to your healthcare team about your risk of ankylosing spondylitis and the symptoms you should watch for.

Find Your Team

On MySpondylitisTeam, the social network for people living with spondylitis and their loved ones, more than 99,000 members come together to ask questions, give advice, and share their stories with others who understand life with spondylitis.

Have you been diagnosed with reactive arthritis? How do you manage your symptoms? Share your tips and experiences in a comment below, start a conversation on your Activities page, or connect with like-minded members in Groups.