BACKGROUND: Anti-ribonucleoprotein (RNP) (auto)antibodies are frequently detected in patients with systemic lupus erythematosus (SLE) although their associations with SLE disease activity remain incompletely understood. We compared patient characteristics, including disease severity outcomes, between adult patients with SLE with or without anti-RNP antibodies (RNP + versus RNP-).
METHODS: We used data from a national, multicentre registry of SLE patients in Australia, collected prospectively between 2007 and 2023. Anti-RNP status and other serological profiles along with demographics were recorded at enrolment. At each routine clinic visit, medication details and disease activity indicators (SLEDAI-2 K, PGA) were captured, and treat-to-target (T2T) states, lupus low disease activity state (LLDAS) and DORIS remission (REM), were determined. Clinical characteristics were compared between RNP + and RNP- patients at 6 months (182 ± 30 days) and 12 months (365 ± 30 days) from enrolment.
RESULTS: A total of 587 patients were studied. 174 (29.6% (95%CI: 26.1%, 33.4%)) were RNP + with significantly higher disease activity and more medication use at enrolment compared with RNP- patients (SLEDAI-2 K median [IQR]: 8.0 [4.0, 10.0] versus 4.0 [2.0, 8.0], p < 0.001; PGA: 0.9 [0.4, 1.2] versus 0.5 [0.2, 1.0], p < 0.001; daily glucocorticoid dose 6.8 [0.0, 15.0] versus 3.0 [0.0, 10.0] mg/day, p < 0.001). RNP + group had more patients with renal, cutaneous, and serological activity. At enrolment, a greater proportion of RNP + patients had active disease (SLEDAI-2 K ≥ 6) compared with RNP- patients (53% versus 41%, p < 0.007), whereas significantly fewer RNP + patients were in LLDAS (20% versus 32.2%, p-value = 0.004) or REM (11.6% versus 22.6%, p-value = 0.006). RNP + patients were 18-fold more likely to be positive for anti-Sm antibodies, and associations with disease activity attenuated upon adjustment for this, though highest disease activity was observed in patients positive to both anti-RNP and anti-Sm autoantibodies (RNP + Sm +). Disease activity indicators between RNP + and RNP- groups converged within the first 12 months following enrolment. Glucocorticoid and immunosuppressant use remained significantly higher in RNP + Sm + patients.
CONCLUSIONS: Anti-RNP positive patients presented with a higher burden of disease activity, and required more intensive treatment with glucocorticoids and immunosuppressants during the first year since study of follow-up, but this was largely driven by the strong association of anti-RNP positivity with anti-Sm positivity.