Objective: To identify the prevalence of serologically active clinically quiescent (SACQ) patients in a cohort of 290 patients with systemic lupus erythematosus (SLE). We investigated if the presence of anti-double-stranded DNA (anti-dsDNA) or antinucleosome (anti-NCS) antibodies during the SACQ period was associated with future flares.
Methods: SACQ patients defined as clinically inactive for 6 months (global British Isles Lupus Activity Group index [BILAG] scores <6) and serologically active (anti-dsDNA antibodies >50 units/ml on at least 2 occasions by enzyme-linked immunosorbent assay [ELISA]) were identified. Patient sera collected during the defined SACQ period were also tested for anti-NCS antibodies (ELISA). We retrospectively reviewed patient clinical details and episodes of flare using the BILAG activity index.
Results: Twenty-seven (9%) patients were SACQ. Seventeen (81%) patients experienced a flare (total of 91 flares, up to 12 flares per person) in the next 5 years. Median duration to first flare was 15 months (range 2-46). Time to first flare after SACQ period was significantly correlated with the presence of anti-NCS (P = 0.0012), high anti-NCS antibody titers (P = 0.0006), and anti-dsDNA titers 5 times above the normal limit (P = 0.02). Patients with higher absolute anti-NCS antibody titers showed a significant correlation with the number of flares (r = 0.57, P = 0.007).
Conclusion: A minority of patients with SLE are SACQ. The majority of these patients experience a flare in the next 5 years and close followup is recommended. Anti-NCS antibodies may be a better predictor than anti-dsDNA antibodies for future flares.