Background:IgG4-related disease (IgG4-RD) is generally considered a chronic fibro-inflammatory condition with insidious presentation and subclinical course. Our clinical experience, however, suggests that a sizable proportion of patients experience multiple accesses to the emergency department (ED), either at disease onset or during the disease course.Objectives:In the present study we aimed (i) to assess the prevalence of acute manifestations of IgG4-RD at disease onset requiring referral to the ED, and (ii) to calculate the diagnostic delay from the initial acute presentation.Methods:We revised our database and identified patients admitted to the ED because of symptoms lately attributed to IgG4-RD onset (Group 1) and those that were referred to our outpatient clinic without previous urgent manifestations (Group 2). Acute manifestations were clustered based on the anatomical district affected by IgG4-RD. Epidemiological, clinical, and serological features of Group 1 and Group 2 were compared.Results:The study included 141 patients with IgG4-RD. 76 (54%) presented to the ED at disease onset. The most common clinical manifestations requiring admission to the ED were jaundice (53%), abdominal pain (41%), and fever (10%). Gastrointestinal involvement was the most frequent cause of referral to the ED (71% of cases), followed by involvement of the retroperitoneum (14.5%), and of the nervous system (6.6%). Pancreato-biliary involvement was significantly more frequent in Group 1. Head, neck, salivary and lacrimal gland involvement was more frequent in Group 2. The diagnostic delay was significantly shorter in Group 1 than in Group 2.Conclusion:Clinical manifestations associated with IgG4-RD onset require referral to the ED in the majority of cases. This finding contrasts with the general view of IgG4-RD as a condition with non-acute presentation.References:[1]Bledsoe JR, Della-Torre E, Rovati L, Deshpande V. IgG4-related disease: review of the histopathologic features, differential diagnosis, and therapeutic approach. APMIS. 2018;126:459-476.[2] Della-Torre E, Lanzillotta M, Doglioni C. Immunology of IgG4-related disease. Clin Exp Immunol.2015;181:191-206.[3]Lanzillotta M, Campochiaro C, Trimarchi M, Arrigoni G, Gerevini S, Milani R, et al. Deconstructing IgG4-related disease involvement of midline structures: Comparison to common mimickers. Mod Rheumatol. 2017;27:638-645.[5]Della-Torre E, Stone JH. “How I manage” IgG4-Related Disease. J Clin Immunol. 2016;36:754-763.[6]Perugino CA, Mattoo H, Mahajan VS, Maehara T, Wallace ZS, Pillai S, et al. Emerging Treatment Models in Rheumatology: IgG4-Related Disease: Insights Into Human Immunology and Targeted Therapies. Arthritis Rheumatol. 2017;69:1722-1732.[7]Stone JH, Zen Y, Deshpande V. IgG4-related disease. N Engl J Med. 2012;366:539-51.[8]Kamisawa T, Zen Y, Pillai S, Stone JH. IgG4-related disease. Lancet. 2015;385:1460-71[9]Umehara H, Okazaki K, Masaki Y, Kawano M, Yamamoto M, Saeki T, et al. Comprehensive diagnostic criteria for IgG4-related disease (IgG4-RD), 2011. Mod Rheumatol. 2012;22:21-30.Disclosure of Interests:Gaia Mancuso: None declared, Emanuel Della Torre: None declared, Marco Lanzillotta: None declared, Giuseppe Alvise Ramirez: None declared, Lorenzo Dagna Grant/research support from: The Unit of Immunology, Rheumatology, Allergy and Rare Diseases (UnIRAR) received unresctricted research/educational grants from Abbvie, Bristol-Myers Squibb, Celgene, Janssen, Merk Sharp & Dohme, Mundipharma Pharmaceuticals, Novartis, Pfizer, Roche, Sanofi-Genzyme, and SOBI., Consultant of: Prof Lorenzo Dagna received consultation honoraria from Abbvie, Amgen, Biogen, Bristol-Myers Squibb, Celltrion, Novartis, Pfizer, Roche, Sanofi-Genzyme, and SOBI.