Beyond diagnosis: exploring the significance of IgG4+ plasma cell count through immunostaining in IgG4-related disease.

Objectives: To evaluate whether the grade of IgG4+ plasma cell infiltration in biopsies is associated with clinical or serologic outcomes in IgG4-RD.

Methods: We included 57 patients with biopsy proven IgG4-RD according to the Comprehensive Diagnostic Criteria and/or the 2019 ACR/EULAR Classification Criteria. We collected histological, clinical (disease duration, phenotype, remission and relapses) and serological variables.

Results: 29 (50.9%) patients were men, mean age 49.9 years, with a median disease duration of 22 months. The distribution among clinical phenotypes were 14% pancreato-hepato-biliary, 12.3% retroperitoneal/aortic, 29.8% head and neck-limited, 29.8% Mikulicz/systemic and 14% undefined. Thirty-nine patients had a proliferative and 18 a fibrotic phenotype. Most biopsies were from lacrimal gland, lymph node, pancreas, orbit, kidney, retroperitoneum and thyroid gland. Thirty-nine (68.4%) patients had <100 IgG4+ plasma cells/HPF and 18 (31.6%) ≥100 IgG4+ plasma cells/HPF. Patients with ≥100 IgG4+ plasma cells/HPF were more likely to belong to the pancreato-hepato-biliary and the proliferative phenotypes, had fewer relapses and a higher remission rate. On multivariate analysis, the OR for remission at last follow-up was 6.7, 95% CI 1.1-4.42, p=0.03. The log-rank test showed a difference in relapse-free survival between the two groups (HR 2.6, 95% CI 1.2-5.6, p=0.01). According to the ROC analysis, patients with more than 61 IgG4+ plasma cells were less likely to relapse.

Conclusions: A count of ≥100 IgG4+ plasma cells/HPF may identify patients with a proliferative phenotype, fewer relapses and a higher remission rate.