Diversity in Acute Autoimmune Pericarditis: Nationwide Analysis of In-Hospital Outcomes and Recurrence.

Background: Acute autoimmune pericarditis (AAP) is an uncommon disease with diverse etiology. Data regarding AAP diagnosis and outcomes are scant.

Objectives: This study sought to describe the diagnosis and the rates of in-hospital mortality, cardiac tamponade, and readmission of AAP.

Methods: This study used a nationwide Japanese claim-based database to identify patients with AAP from April 2016 to March 2020 compared with patients with acute idiopathic pericarditis (AIP).

Results: Of 20,469 hospitalized patients with acute pericarditis, 170 had AAP and 5,027 had AIP of new onset. The diagnosis for AAP was systemic lupus erythematosus in 23.5% (40 of 170), rheumatoid arthritis in 19.4% (33 of 170), systemic sclerosis in 8.2% (14 of 170), other in 17.7% (30 of 170), and undifferentiated in 31.2% (53 of 170). During hospitalization, 1.8% (3 of 170) of patients with AAP and 1.5% (73 of 5,027) of patients with AIP died, and cardiac tamponade occurred in 8.8% (15 of 170) of AAP patients and 4.7% (237 of 5,027) of AIP patients. The incidence of cardiac tamponade was highest in patients with systemic lupus erythematosus (15.0%; 6 of 40). AAP was more associated with cardiac tamponade than AIP (adjusted OR: 1.82; 95% CI: 1.02-3.23). There was no difference between the AAP and AIP groups with regard to rehospitalization, although this was more common in patients with undifferentiated forms of autoimmune disease ( = 0.001).

Conclusions: This Japanese national registry study of acute pericarditis revealed no differences in rehospitalization for recurrence between patients with AAP and AIP. It also underscored the diversity in AAP diagnosis, with more than 30% of patients lacking a differentiated diagnosis.