AB1417 SEROLOGICAL ELEVATION OF IgG4 AND CLINICAL CORRELATION
Authors: P. Martinez Calabuig, J. J. Fragío Gil, R. González-Mazarío, L. Salvador Maicas, M. L. Sanmartín Martínez, S. Moner Marín, A. Sierra Rivera, A. Rueda Cid, J. J. Lerma Garrido, C. Molina Almela, C. Campos Fernández
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> IgG4-related disease (IgG4-RD) is a rare, systemic, immunomediated fibroinflammatory process with uncertain etiology and pathophysiology that can affect multiple organs, presenting common clinical, radiological, and serological characteristics. Although the disease is associated with IgG4, serum levels are not elevated in all patients; it has also been described in other respiratory system diseases (bronchiectasis, asthma, sarcoidosis), pancreatic diseases (chronic pancreatitis), liver diseases (cirrhosis), or in relation to other autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), or inflammatory myopathies. <h3>Objectives:</h3> To determine the prevalence and clinical significance of IgG4 positivity in the blood of patients with an initial suspicion of systemic autoimmune disease. <h3>Methods:</h3> A single-center cross-sectional study was conducted, in which all results from the electronic medical records of patients with elevated IgG4 (&gt;135 mg/dL) from a single center and requested by various hospital departments from January 2010 to August 2022 were analyzed. Demographic data were collected, as well as final diagnoses, including those with IgG4-RD. <h3>Results:</h3> A total of 182 patients with serological elevation of IgG4 were reviewed (Table 1). Of the patients analyzed, only 13 met the diagnostic criteria for IgG4-RD according to the Umehara-Okazaki 2011 criteria, and 7 met the ACR/EULAR 2019 criteria. Among the remaining patients, the majority (45.1%) presented with respiratory pathology, mostly comprising patients with COPD (13.19%), bronchiectasis (8.79%), or asthma (5.5%). An elevation of IgG4 was also observed in other systemic autoimmune diseases (20.33%), being more frequent in patients diagnosed with SLE (3.3%), RA (2.2%), or EGPA (2.75%); or patients diagnosed with some malignancy (10.99%), most frequently in pulmonary (3.3%) or pancreatic and biliary tract cancers (2.2). Finally, elevation of this immunoglobulin was also observed in patients with digestive pathology (9.34%), especially in patients with pancreatitis (6.04). <b>Table 1.</b> Variables Collected from Patients with Elevated IgG4 <h3>Conclusion:</h3> The study reflects that an elevation of IgG4 is not exclusive to IgG4-related disease (IgG4-RD), also appearing in various respiratory pathologies (COPD, bronchiectasis, asthma), autoimmune diseases (SLE and RA), and neoplasms. These data suggest that high levels of IgG4 could indicate a more generalized immunological reaction and would not be useful as a screening tool for IgG4-RD. <h3>REFERENCES:</h3> [1] Stone JH, Zen Y, Deshpande V. IgG4-related disease. N Engl J Med. 2012 Feb 9;366(6):539-51. [2] Iaccarino L, Talarico R, Scirè CA, Amoura Z, Burmester G, Doria A, et al. IgG4-related diseases: state of the art on clinical practice guidelines. RMD Open. 2019 Jan 19;4(Suppl 1):e000787. [3] Wallace ZS, Naden RP, Chari S, Choi H, Della-Torre E, Dicaire JF, et al; The 2019 American College of Rheumatology/European League Against Rheumatism Classification Criteria for IgG4-Related Disease. Arthritis Rheumatol. 2020 Jan;72(1):7-19. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>