Often Misdiagnosed, Adults with pJIA Have Distinct Clinical Features from Rheumatoid Arthritis Patients, Study Reports

Often Misdiagnosed, Adults with pJIA Have Distinct Clinical Features from Rheumatoid Arthritis Patients, Study Reports

Adults with polyarticular juvenile idiopathic arthritis have distinct clinical features from those with rheumatoid arthritis, with greater prevalence of tumor necrosis factor inhibitors, a study reports.

The study, “Comparison of Adults With Polyarticular Juvenile Idiopathic Arthritis to Adults With Rheumatoid Arthritis: A Cross-sectional Analysis of Clinical Features and Medication Use,” was published in the Journal of Clinical Rheumatology.

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease that affects the joints at a young age. Children with polyarticular JIA (pJIA) have inflammation on more than five joints.

About 37%–60% of children with JIA are estimated to have active disease when they reach adulthood. However, when they transition from a pediatric to an adult rheumatology clinic, they are more likely to be misdiagnosed with rheumatoid arthritis (RA).

Misdiagnosis impacts not only studies about disease outcomes, but also treatment recommendations: for example, nonbiological combination disease-modifying antirheumatic drugs (DMARD) are usually mostly considered for rheumatoid arthritis.

“The ideal treatment for the adult [polyarticular] JIA patient is not known, and recommendations are generally extrapolated from the pediatric JIA and adult RA populations,” the researchers wrote, adding that to understand the impact of treatment on the outcome of adults with polyarticular JIA, “the unique characteristics of this population must be more clearly defined.”

Therefore, researchers at Penn State College of Medicine investigated to identify the clinical characteristics that distinguish adult patients with polyarticular JIA from those with rheumatoid arthritis.

The researchers evaluated 45 adults with polyarticular JIA and 94 with rheumatoid arthritis who were followed at the Penn State Hershey Medical Center System between January 2013 and June 2015. JIA patients had been previously diagnosed with JIA by a pediatric rheumatologist.

Overall, adults with polyarticular JIA were younger (27.4 years was the average age) than those with rheumatoid arthritis (56.1 years). In both groups, most patients were female (88.9% JIA patients and 73.4% RA patients).

Polyarticular JIA patients had a longer disease duration (mean of 20.6 years) than the rheumatoid arthritis group (11.1 years). They were also less likely to be positive for rheumatoid factor (RF, 29%) compared to those with rheumatoid arthritis (78.3%). This tendency was seen when researchers analyzed the levels of a molecule called anti-cyclic citrullinated peptide (CCP), where 28.6% of JIA patients tested positive compared with 74.4% of RA patients.

RF and CCP are two antibodies whose levels are generally higher in rheumatoid arthritis patients.

Using two disease classification systems, the 1987 and 2010 Rheumatoid Arthritis Criteria, the researchers found that patients with polyarticular JIA had 88% lower odds of meeting the 2010 criteria for a rheumatoid arthritis diagnosis compared with rheumatoid arthritis patients.

In addition, more polyarticular JIA patients (66.7 %) had a history of methotrexate use (brand names Trexall, Otrexup, among others) — a DMARD that reduces immune system activity and is a first line treatment for both conditions — than those with rheumatoid arthritis (39.4%). Current use was similar between both groups.

Disease duration was found to be a predictor for methotrexate initiation and that for each additional year of disease, the average time to start methotrexate increased by 14%.

More than 48% of JIA patients were using tumor necrosis factor (TNF) inhibitors: 33.3% of the patients in the polyarticular JIA group were currently prescribed Enbrel (etanercept) compared with 8.5% in the rheumatoid arthritis group.

Thirty five percent of rheumatoid arthritis patients were using hydroxychloroquine, an anti-inflammatory sold as Plaquenil (among other brand names) compared with 6.7% in the JIA group.

“Although often considered together in adult rheumatology practice, adults with [polyarticular] JIA are distinct from patients with [rheumatoid arthritis],” the researchers wrote.

“Medication use markedly differed between the [two] populations with greater prevalence and duration of TNFi [inhibitors] use in pJIA patients. Further study is needed to improve outcomes in this unique population,” they concluded.

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