Background: Diagnosing IgG4-related periaortitis/retroperitoneal fibrosis (IgG4-PA/RPF) without biopsy of PA/RPF lesions is often challenging owing to various secondary causes of PA/RPF.

Objectives: This study was aimed at exploring clinical findings other than those of PA/RPF biopsy that may be useful for differentiating IgG4-PA/RPF from mimickers.

Methods: In this multicenter cross-sectional study, we analyzed 75 Japanese patients diagnosed with IgG4-related disease (IgG4-RD) having cardiovascular and/or retroperitoneal manifestations, along with 20 mimickers identified by experts. We performed an intergroup comparison of clinical characteristics other than biopsy findings of PA/RPF lesions between IgG4-RD and mimickers. In addition, factors related to the final diagnosis of IgG4-RD by experts were assessed by age-, sex-, and serum IgG4 level-adjusted logistic regression analyses.

Results: The final diagnoses of mimickers mainly consisted of Takayasu arteritis, giant cell arteritis, infectious aortic aneurysm, lymphoma, plasmacytoma, and urinary tract carcinoma. Compared with mimickers, IgG4-PA/RPF was associated with higher levels of serum IgG4 and IgE; higher eosinophil counts; lower levels of serum C3, C4, CH50, and C-reactive protein; male predominance; allergic predisposition; fewer cases with physical pain and/or fever; fewer instances of thoracic aorta involvement; more iliac artery involvement; prevalence of major extra-PA/RPF lesions of IgG4-RD; and higher inclusion scores of the American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria [1]. Age-, sex-, and serum IgG4 level-adjusted logistic regression analysis indicated that iliac artery involvement [odds ratio (OR) 8.701, 95% confidence interval (CI) 1.006-75.243], presence pf extra-PA/RPF lesions (OR 9.097, 95% CI 1.055-78.419), and inclusion scores of the ACR/EULAR classification criteria for IgG4-RD (OR 1.155, 95% CI 1.025-1.301) were positively related to a final diagnosis of IgG4-RD. However, two cases of follicular lymphoma with periaortic lesions, paravertebral lesions in the thorax, renal pelvic lesions, and/or focal pancreatic lesions could be differentiated only based on biopsy.

Conclusion: The present study suggests that in the absence of PA/RPF biopsy findings, iliac artery involvement, presence pf extra-PA/RPF lesions, and high inclusion scores of the ACR/EULAR classification criteria for IgG4-RD are useful for differentiating IgG4-PA/RPF from mimickers. Nevertheless, biopsy is still necessary to differentiate some cases of low-grade lymphoma from IgG4-RD.

REFERENCES: [1] Wallace ZS, et al. The 2019 American College of Rheumatology/European League Against Rheumatism classification criteria for IgG4-related disease. Ann Rheum Dis. 2020;79:77-87.

Acknowledgements: We sincerely thank all the members of Department of Nephrology and Rheumatology, Kanazawa University Hospital.

Disclosure of Interests: None declared.