As one might expect, patients with monoarthritis, or the inflammation of a single joint, tend to have better prognoses than those whose disease impacts multiple joints. So it follows that researchers have focused more on the more complicated polyarthritis than monoarthritis, explains Ellen Sauar Norli, a rheumatologist at Norway’s Martina Hansens Hospital.

“Other reasons why there are few studies on patients with recent-onset monoarthritis might be that patients with monoarthritis are more often initially taken care of by general practitioners,” says Norli, lead author of a new study published in Arthritis Care & Research. “The arthritis might resolve before the patient is seen by a rheumatologist.”

Norli and colleagues studied joint distribution and two-year outcomes among 347 patients with monoarthritis of less than 16-weeks duration. About a third of the patients had monoarthritis at the beginning of the study, and a quarter appeared to develop chronic inflammatory rheumatic disease.

The most frequently affected joints were knees (49.3 percent), ankles (16.7 percent), and wrists (14.1 percent), and 91 of the patients (26.2 percent) developed chronic inflammatory disease. Of the latter, 21 (6.1 percent) had RA and 16 (4.6 percent) had psoriatic arthritis.

[Read more about rheumatoid arthritis symptoms.]

Joint diseases, Norli says, vary according to the typical involvement of the affected joints. RA, the most common chronic inflammatory rheumatic disease, tends to impact small joints in hands and feet, while ankles and knees tend to be impacted in spondyloarthritis.

“If monoarthritis is the start of a chronic inflammatory disease, one could expect that inflammation of one small joint more often would predict rheumatoid arthritis, than inflammation of one large joint,” Norli says.

Patients with monoarthritis in their ankles had a particularly small chance of developing chronic inflammatory rheumatic disease. None in the study had RA or psoriatic arthritis.

“Baseline factors associated with developing one of these diseases were wrist involvement, female sex, smoking, lengthy duration of swelling, positive ACPA (anti-citrullinated protein antibodies) and RF (rheumatoid factor), and elevated erythrocyte sedimentation rate,” reports MedPage. “Almost 60 percent were treated with DMARDs (Disease-modifying antirheumatic drugs), while half also were given systemic corticosteroids. Only 13 percent of those who did not develop the chronic inflammatory diseases received corticosteroids.”

[Learn what it feels like to have rheumatoid arthritis.]

But it’s difficult to say why monoarthritis in the wrist doubled the chance of rheumatic disease, while its presence in the ankle halved that likelihood.

“I don’t have the full answer to this question,” Norli says. “Moreover, these are the results of one study, and further studies of recent-onset monoarthritis are needed.”

The fact that different joints are susceptible in different ways to different diseases may partially explain her and her colleagues’ results. “Of the 58 patients with ankle monoarthritis, 17 percent had a reactive arthritis diagnosis (most often self-limiting) at baseline, whereas this was the case for only 4 percent of the 49 patients with wrist monoarthritis,” she says.

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