Discriminative features of immunoglobulin G4-related disease (IgG4-RD) and associated autoimmune rheumatic diseases (ARDs) in a nationwide observational cohort: study from the Egyptian College of Rheumatology.

Objective: The objective of this study is to present the clinical characteristics of immunoglobulin G4-related diseases (IgG4-RD) patients and describe associated overlap with autoimmune rheumatic diseases (ARDs).

Patients And Methods: This cross-sectional study included 81 patients with IgG4-RD who were recruited from 13 specialized rheumatology departments and centers across the country in collaboration with the Egyptian College of Rheumatology (ECR). Patients underwent a thorough history-taking and clinical examination. We reviewed patients' medical records and recorded the medications they used. The presence of comorbidities or cumulative manifestations was determined. Laboratory investigations, imaging, and biopsy histopathology were assessed.

Results: The mean (SD) age was 41.4 (14.6) years with 60 females and 21 males (F/M 2.9:1). The diagnosis was definite in 50 (61.7%), probable in 19 (23.5%), and possible in 12 (14.8%). The most common cumulative clinical features are IgG4-related respiratory disease in 19 (23.5%), autoimmune pancreatitis (AIP) in 18 (22.2%), and Riedel's thyroiditis in 17 (21.0%). Approximately 80% were administered corticosteroids, whereas 40% received azathioprine as adjunct therapy. Approximately 16% developed a relapse with this combination and transitioned to an alternative steroid-sparing treatment. Twelve individuals (14.7%) required rituximab. Fifty percent of patients receiving rituximab (six patients) exhibited complete improvement, while the remaining had partial improvement. Ten (12.3%) patients had associated ARDs: five (6.2%) with systemic lupus erythematosus (SLE), four (4.9%) with rheumatoid arthritis (RA), and one with vasculitis. Of the four patients with associated RA, three were rheumatoid factor (RF) negative. IgG4 was in all cases, RF was positive in 18.5%, and antinuclear antibody was in 14.7%.

Conclusion: IgG4-RDs exhibit a wide range of presentations, closely associated with ARDs. Awareness among clinicians about this condition will increase their consideration and rate of prompt diagnosis, which is essential to prevent damage to critical organs. Key Points • IgG4-RDs have a myriad spectrum of presentation with a close link to rheumatic diseases. • Awareness among clinicians about this condition will increase their consideration and rate of prompt diagnosis. • The lack of reliable biomarkers for this condition has been an important hurdle for diagnosis.