Exploring the clinical characteristics and long-term outcome of serologically active clinically quiescent...

In the long-term management of IgG4-related disease (IgG4-RD), it is common to observe clinical remission accompanied by elevated IgG4 levels, namely, serologically active clinically quiescent (SACQ). We aimed to determine and characterize the SACQ status in IgG4-RD and evaluate its prognosis.

We performed this single-center study based on a prospective IgG4-RD cohort. SACQ and serologically quiescent clinically quiescent (SQCQ) were defined as clinical remission with elevated but steady (for SACQ)/normal (for SQCQ) serum IgG4 for at least two years. Characteristics and prognoses between the SACQ and SQCQ groups were compared. Univariate and multivariate Cox regressions were used to investigate risk factors for relapse in SACQ patients.

The study included 268 SACQ and 108 SQCQ patients with IgG4-RD. Compared to the SQCQ group, the SACQ group had higher baseline levels of IgG4 and a greater prevalence of proliferative subtype (both P < 0.001). Plasmablasts were increased, while unswitched memory B cells and regulatory B cells were decreased in SACQ patients compared with SQCQ patients. Both groups experienced glucocorticoid (GC) tapering and had similar relapse rates (P = 0.659) during an average follow-up of 55 months, although the SACQ group was at a higher GC maintenance dose. In the SACQ group, serum IgG4 level re-elevation to ≥ 1.269 times the start of SACQ status was associated with relapse (HR 1.40, 95% CI: 1.16-1.42, P < 0.001; AUC = 0.791).

SACQ patients achieved outcomes similar to SQCQ with cautious GC tapering. Monitoring serum IgG4 re-elevation might be useful for predicting relapses in the long-term management of SACQ status in IgG4-RD. Key Points • During clinical remission in IgG4-RD, a considerable proportion of patients still have elevated serum IgG4, which we first define as serologically active and clinically quiescent (SACQ). • SACQ patients achieved relapse rates similar to SQCQ patients with cautious glucocorticoid tapering. • Monitoring serum IgG4 re-elevation might help predict relapses in the long-term management of IgG4-RD SACQ patients.