Reactive Arthritis

When your joints react to an infection somewhere else. The fifth post in our spondyloarthritis series.

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This is the fifth post in our spondyloarthritis series. Today is reactive arthritis, a condition that's relatively uncommon but important to recognize because the treatment can differ meaningfully from the rest of the group.

Reactive arthritis is joint inflammation that develops in response to an infection somewhere else in the body. The joints themselves aren't infected. Instead, the immune system's response to an infection at another site triggers an inflammatory reaction in the joints, usually a few weeks after the original infection.

This is part of why it can be tricky to diagnose. By the time the joint symptoms appear, the original infection has often resolved, and patients don't always make the connection.

A note on the name

You may come across the term "Reiter's syndrome" in older literature or online resources, particularly if you do your own research. Reiter's syndrome was historically used to describe a specific form of reactive arthritis with the triad of arthritis, urethritis, and conjunctivitis.

The name was retired in the early 2000s after broader recognition that Hans Reiter, the German physician the condition was named for, was a Nazi war criminal who conducted experiments on concentration camp prisoners. Major rheumatology journals formally moved away from the eponym in 2003. The condition is now uniformly called reactive arthritis.

Triggers

The classic causes include:

• GI infections. Salmonella, Shigella, Campylobacter, Yersinia, and C. difficile are the bacterial culprits historically described. Viral gastroenteritis can do it too, and is probably underrecognized as a trigger.

• Genitourinary infections. Chlamydia trachomatis is the most common. This is the one where the distinction matters most, because untreated Chlamydia needs antibiotic treatment in its own right.

• Other infections. Reactive arthritis has also been reported after COVID-19, strep throat (post-streptococcal reactive arthritis is its own recognized entity), and a range of other viral illnesses.

Joint symptoms typically appear one to four weeks after the original infection. By then the GI bug or UTI is often gone, which is part of why the connection gets missed.

A different beast: gonococcal arthritis

Worth distinguishing reactive arthritis from gonococcal arthritis, which is a different process. Gonococcal arthritis is a direct infectious arthritis. The bacteria (Neisseria gonorrhoeae) actually get into the joint and cause infection there. The treatment is targeted antibiotics, joint drainage if needed, and prompt management because untreated septic arthritis can damage the joint quickly.

Reactive arthritis after Chlamydia, in contrast, is an immune-mediated process. The joints themselves aren't infected. The treatment approach for the joint inflammation is different, although the Chlamydia infection itself does need antibiotic treatment.

The distinction matters for diagnosis and management.

What it looks like

Reactive arthritis typically presents with:

• Asymmetric arthritis, often involving the lower extremities (knees, ankles, feet)

• Enthesitis (especially the heels)

• Dactylitis (the "sausage digit")

• Inflammatory back pain in some patients, particularly if HLA-B27 positive

• Eye inflammation (conjunctivitis or uveitis)

• Skin findings in some cases (keratoderma blennorrhagicum, circinate balanitis)

• Mouth ulcers

Like other spondyloarthritis subtypes, patients are often HLA-B27 positive, which seems to predispose to a more severe and prolonged course.

Diagnosis

The diagnosis is clinical and depends heavily on the history of a recent infection. When I see a patient with new asymmetric joint inflammation, I ask about recent GI illness, recent UTI symptoms, recent sexual activity (for Chlamydia exposure), recent sore throat, or recent viral illness.

Labs help support the diagnosis. Inflammatory markers (ESR, CRP) are often elevated. HLA-B27 status can be useful. Stool studies or urogenital testing for Chlamydia may be appropriate depending on the suspected trigger. Joint fluid analysis, when done, is sterile (no organisms grow) and typically inflammatory, which distinguishes it from septic arthritis.

This is one of those situations where catching the trigger matters. If Chlamydia is the cause, that needs to be treated. If gonococcal arthritis is on the differential, that needs to be ruled out, because the treatment is very different.

Course

The good news with reactive arthritis is that it's often self-limited. Most patients improve within three to six months, and many fully recover.

A subset, though, have a chronic course. Persistent or recurrent reactive arthritis is more common in HLA-B27 positive patients and in those with severe initial presentations. In these cases, the condition can look more like the other chronic spondyloarthritis subtypes and require longer-term management.

Treatment

A few cornerstones:

• Treat the trigger. If Chlamydia is identified, it needs to be treated with antibiotics. The same goes for any other active infection. Importantly, antibiotics generally don't change the course of the joint disease once the reactive process has been triggered, but treating the underlying infection is still essential.

• NSAIDs. First-line for joint symptom control in most cases.

• Intra-articular steroid injections. Useful when one or two joints are particularly active.

• Sulfasalazine or methotrexate. Considered for patients with persistent disease beyond a few months.

• TNF inhibitors and other biologics. Reserved for chronic, severe reactive arthritis that doesn't respond to the above. Most patients don't need to escalate this far.

The treatment ladder is generally lighter than for the other spondyloarthritis subtypes because most cases resolve. The goal is symptom control while the immune response settles down.

Summary

Reactive arthritis is uncommon but worth recognizing. The clue is the timing: new asymmetric joint pain or back pain a few weeks after a GI bug, UTI, or other infection. Most cases resolve, but identifying the trigger matters, especially if it's a treatable infection like Chlamydia.