Reactive arthritis that is due to chlamydia transmission is infection responds to antibiotic therapy. Other infectious causes of the condition do not.

So it is worth checking the synovial fluid of affected joints for evidence of chlamydia polymerase chain reaction (PCR), according to Dr. Atul Deodhar, professor of medicine at Oregon Health and Science University in Portland.

In a recent randomized trial, 6 months of rifampin plus either azithromycin or doxycycline significantly improved outcomes versus placebo in patients with chlamydia-induced reactive arthritis. Synovial fluid PCRs were positive for chlamydia in all 42 patients (Arthritis Rheum. 2010;62:1298-307).

The study "has changed my practice. I now send synovial fluid for PCR. I have found several patients" positive for chlamydia, "and we are treating them with antibiotics," Dr. Deodhar said; he also sends urine samples for chlamydia testing.

The primary end point in the study – an improvement of 20% or more in at least four of six variables such as swollen joint count – was achieved by 17 of 27 antibiotic patients (63%) but only 3 of 15 placebo patients (20%). Six patients treated with antibiotics but none of the patients in the placebo group went into complete remission during the trial. Patients on antibiotic were also more likely to clear chlamydia from their joints.

It’s a different story when reactive arthritis is triggered by gastrointestinal pathogens such as salmonella, shigella, campylobacter, and yersinia. In those cases, "avoid antibiotics," Dr. Deodhar said.

He and his colleagues found antibiotic therapy just didn’t help in a population study of 575 likely reactive arthritis cases among 6,379 people with culture-confirmed GI infections. His team confirmed reactive arthritis in 54 of the 82 (66%) subjects they were able to exam. Enthesitis was the most frequent finding; arthritis was less common (Ann. Rheum. Dis. 2008;67:1689-96).

Some patients had been given antibiotics for their GI infections, others not. It "didn’t really make any difference to patients developing or not developing reactive arthritis or the severity of it. Antibiotics are not going to prevent people with dysentery from developing reactive arthritis," Dr. Deodhar said.

They also found that the presence or absence of human leukocyte antigen B27 did not predict risk. In sporadic reactive arthritis cases, the presence of the antigen is "not actually that important in deciding if someone has or does not have reactive arthritis," he said.

Onset of reactive arthritis comes a few days to a maximum of several weeks following the inducing infection. Asymmetrical mono- or oligoarthritis of the lower extremity is the most common joint finding. Uveitis, dactylitis, and enthesitis are also possible.

Besides antibiotics for chlamydia-induced disease, sulfasalazine and tumor necrosis factor inhibitors may help with difficult cases.