Differential sensitivity of the 2020 revised comprehensive diagnostic criteria and the 2019 ACR/EULAR classification criteria across IgG4-related disease phenotypes: results from a Norwegian cohort

BACKGROUND: We investigated sensitivity of the 2020 Revised Comprehensive Diagnostic Criteria (RCD) and the 2019 ACR/EULAR classification criteria across the four identified IgG4-related disease (IgG4-RD) phenotypes: “Pancreato-Hepato-Biliary”, “Retroperitoneum and Aorta”, “Head and Neck-limited” and “Mikulicz’ and Systemic” in a well-characterized patient cohort. METHODS: We included adult patients diagnosed with IgG4-RD after comprehensive clinical assessment at Oslo University Hospital in Norway. We assigned patients to IgG4-RD phenotypes based on pattern of organ involvement and assessed fulfillment of RCD and 2019 ACR/EULAR classification criteria. Differences between phenotype groups were analyzed using one-way ANOVA for continuous variables, and contingency tables for categorical variables. RESULTS: The study cohort included 79 IgG4-RD patients assigned to the “Pancreato-Hepato-Biliary” (22.8%), Retroperitoneum and Aorta” (22.8%) “Head and Neck-limited” (29.1%), and “Mikulicz’ and Systemic” (25.3%) phenotype groups, respectively. While 72/79 (91.1%) patients in total fulfilled the RCD, proportion differed across phenotype groups and was lowest in the “Retroperitoneum and Aorta” group (66.7%, p < 0.001). Among the 57 (72.2%) patients meeting the 2019 ACR/EULAR classification criteria, proportion was again lowest in the “Retroperitoneum and Aorta” group (27.8%, p < 0.001). CONCLUSION: The results from this study indicate that IgG4-RD patients having the “Retroperitoneum and Aorta” phenotype less often fulfill diagnostic criteria and classification criteria than patients with other IgG4-RD phenotypes. Accordingly, this phenotype is at risk of being systematically selected against in observational studies and randomized clinical trials, with potential implications for patients, caregivers and future definitions of IgG4-RD.