Background/Purpose: Seronegative rheumatoid arthritis (SnRA) and undifferentiated arthritis (UA) are heterogeneous conditions that share many clinical features with other systemic rheumatic diseases. Patients initially diagnosed with SnRA or UA are often reclassified to more specific diagnoses.

We report a retrospective chart review from the military health system (MHS) that examines the clinical characteristics of SnRA and UA, and the degree to which they are reclassified over time.

Methods: The study included MHS beneficiaries diagnosed with SnRA or UA diagnosed in 2016 or 2017. The inclusion criteria consisted of a negative rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibody at presentation, synovitis on a rheumatologist’s exam, and treatment with a disease modifying anti-rheumatic drug (DMARD).

Patients were excluded if chart review revealed an alternative diagnosis. We obtained data including the number of clinic visits, the number and distribution of involved joints, DMARD use, the presence or absence of erosions, and any extra-articular manifestations at presentation. We then analyzed these data for potential predictors of future diagnostic reclassification.

Results: 1338 patients were screened, and 133 patients were included. Of the included patients, the index diagnosis was SnRA in 20 (17.7%) patients, and UA in 113 (85%) patients. 74 (55.6%) were female, and 59 (44.3%) were male. Of the included patients with an index diagnosis of SnRA, 13 (65%) met the 2010 ACR classification criteria for RA. 85 (63.9%) of the included patients were later reclassified to other diagnoses. Reclassification diagnoses included SnRA (52.1%), SpRA (9.4%), PsA (14.6%), SpA (14.6%), and other (9.4%).

Using binomial logistic regression, we analyzed the relationship between diagnostic reclassification and multiple predictors including the age of diagnosis, the number of clinic visits, the number of transitions of care, and the distribution of joint involvement.

The model was statistically significant (X2(7) = 15.747, p = 0.028) and explained 15% of the variance in diagnostic reclassification (Nagelkerke R2). While most predictor variables failed to reach significance, more clinic visits were associated with greater odds of diagnostic reclassification (OR 1.07, CI 1.03-1.12).

In the reclassified group, the average number of clinic visits was 18.5 (IQR 10-25) over 7 years compared to 12 (IQR 6-16.5) over 6.7 years in the not reclassified group, which is a difference in average follow-up of every 4.5 vs 6.7 months.

Looking for other potential differences between the reclassification diagnoses, we used Chi-Squared testing to compare treatment modalities and the presence of extra-articular features. No significant differences were found in treatment patterns. The only difference in extra-articular features was seen in the PsA group, which had higher rates of cutaneous features.

Conclusion: Our data may indicate a potential association with the frequency of follow-up clinic visits with the likelihood of future diagnostic reclassification in SnRA and UA, suggesting that more frequent follow up for these patients may improve diagnostic accuracy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/outcomes-in-seronegative-rheumatoid-arthritis-and-undifferentiated-arthritis/