Background: Acute myocarditis (AM) may be the heralding manifestation of autoimmune and inflammatory disorders (AIID). We aimed to describe the clinical presentation and outcome of patients with AM revealing AIID.

Methods: All consecutive adult patients with AM admitted in a department of Cardiology (Bichat Hospital, Paris, France) from January 2011 to January 2019 were included. Diagnosis of AM was based on clinical manifestations, elevated Troponin, myocardial inflammation on CMR and no evidence for coronary artery disease. AIID were classified using international criteria.

Results: Two-hundred and eighteen (35.3 [26.4-47.1] years, 75.2% males) patients with AM were included. Overall, AM revealed AIID in 15 (6.9%), including systemic lupus erythematosus (n = 3), adult onset Still’s disease (n = 3), sarcoidosis (n = 2), mixed connective tissue disease (n = 1), anti-Jo1 syndrome (n = 1), eosinophilic granulomatosis with polyangiitis (n = 1), antiphospholipid syndrome (n = 1), reactive arthritis (n = 1), Graves’ disease (n = 1) and Crohn’s colitis (n = 1). Left ventricular ejection fraction (LVEF) at onset was <30% in 5 (33.3%) patients with AIID. All but 2 patients with AIID were treated with steroids, immunosuppressive and/or immunomodulatory drugs and LVEF normalized in all by the end of follow-up. By comparing patients with AIID to patients with idiopathic AM (n = 203), multivariable analysis showed that pericardial effusion, lack of chest pain and high CRP level at onset were independently associated with AIID.

Conclusion: Acute myocarditis revealing AIID may be life-threatening at the acute phase but has an overall good prognosis under specific treatment. Pericardial effusion and CRP level at admission suggest an AIID as the cause for AM.