Background/Purpose: We aimed to study the prevalence of subtypes of lupus arthritis and determine their association with clinical features, serology, and type I interferon signature.

Methods: This is a retrospective analysis of a prospective SLE cohort with arthritis defined by the ACR or EULAR/ACR SLE classification criteria at presentation and SLEDAI 2K over follow-up identified from a single-center SLE database (July 1970-Aug 2024) from both inception and prevalent cohorts. Demographic, clinical, laboratory (including interferon signature), radiographic features, and treatment variables were retrieved from the database. Descriptive statistics were used to outline features across three subtypes of arthritis: ND arthritis (determined by clinical examination), arthritis with reducible deformities or Jaccoud’s Arthropathy (JA), and arthritis with non-reducible deformities or rhupus. Factors associated with deforming arthritis were determined using binary logistic regression, including age, sex, disease duration, antibodies, adjusted mean SLEDAI-2K, and Type 1 IFN scores. Time to deformities and predictors were studied in the inception subgroup using fine and gray time-to-event analyses.

Results: Arthritis was observed in 1,248 of 2264 (55.12%) patients, of whom 908 (72.6%) had ND, 239 (19.2%) had JA, 101 (8.1%) had rhupus. The median age at diagnosis of SLE was comparable, though a higher proportion of females was observed in JA (p=0.03).The distribution of organ involvement and antibodies was similar across the three subtypes, except nervous system involvement (p=0.03) and anti-Ro antibodies (p=0.04) being more frequent in rhupus. Rheumatoid factor and anti-citrullinated protein antibody positivity did not differ significantly. The proportion of patients with high interferon signature was the highest in JA, followed by ND arthritis, and lastly, rhupus (p< 0.01). Radiographs (n, 95) revealed erosive disease in 10 of 43 (23.2%) with JA, 12 of 36 (33.3%) with rhupus, and 2 of 16 (12.5%) with non-deforming arthritis. (Table 1)In the multivariable analysis, rhupus was associated with a lower odds for a high type I IFN signature (0.20 [0.07, 0.56]) with a direction of positive association towards rheumatoid factor (3.04 [0.97, 9.51] and anti-Ro (2.75 [0.91, 8.33]) positivity when compared with ND arthritis. No associations were observed with JA when compared with ND arthritis. (Figure 1)The time to development of deformities from enrollment was 2.07 (1.15, 7.6) years for JA and 4.64 (1, 9.78) years for rhupus within the inception cohort. Anti-RNP was predictive of JA on multivariable analysis [4.88 (1.02, 23.5)].

Conclusion: Arthritis was observed in half the cohort, with the majority being non-deforming. Among deforming arthritis, JA was more common than rhupus. JA and ND arthritis were associated with a high IFN signature score while rhupus was characterized by a low IFN signature score. This sheds light on two different mechanisms for deforming arthritis in SLE. Erosions were observed in both types of deforming arthritis blurring the line of radiologic differences historically outlined between them.

Table 1: Demographic, clinical and treatment characteristics of the cohort

Figure 1: Multivariable logistic regression analyses to identify associations with Jaccoud’s and rhupus, non-deforming arthritis being the reference. (n=318)

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterizing-arthritis-subtypes-in-sle-prevalence-clinical-features-and-the-role-of-type-i-interferon-signatures/