Natural History of Patients With Histologically Proven Acute Eosinophilic Myocarditis

Acute Eosinophilic Myocarditis is a rare form of heart inflammation caused by the accumulation of eosinophils, a type of white blood cells, within the heart muscle. Among the few patients who undergo heart biopsy for suspected myocarditis, eosinophilic forms account for a small percentage of cases, estimated at about 5–15% of myocarditis with complications. The disease may be associated with systemic conditions such as eosinophilic granulomatosis with polyangiitis (EGPA), hypersensitivity reactions to medications, hypereosinophilic syndromes, inflammatory bowel diseases, infections or blood disorders, although in many patients no clear cause is identified (i.e.: the so-called idiopathic forms).

Inflammation of the heart muscle can reduce its ability to pump blood effectively. Patients may experience shortness of breath (which is the most common symptom at presentation), chest pain, fever or marked fatigue, and in some cases the disease can progress rapidly and require intensive medical care. Because previous knowledge was based mainly on small case series, the overall course of the disease and its long-term implications were not well defined.

To address this gap, researchers from 53 hospitals across Europe, North America, Asia and Australia created the largest International Registry of patients with biopsy-proven acute eosinophilic myocarditis. The study included 156 patients, with a median age of 48 years.

One of the key findings is that eosinophilic myocarditis (EM) does not always present with elevated eosinophil levels in the blood. In many patients, routine blood tests alone would not have suggested the diagnosis. This underlines the importance of careful clinical evaluation and, when appropriate, endomyocardial biopsy to confirm the clinical suspicion and guide treatment decisions.

Many patients were seriously ill at admission and required advanced supportive treatment.
Early clinical features helped identify patients at higher risk. In particular, lower systolic blood pressure and reduced left ventricular ejection fraction (a marker for the heart´s pumping function measured by imaging techniques like e.g. echocardiography/cardiac ultrasound) were associated with a more complicated course.

Cardiac magnetic resonance imaging (cardiac MRI), a detailed heart scan taking highly detailed, 3D pictures, provided further useful information. In most patients, the scan showed areas of heart muscle injury using a contrast technique called late gadolinium enhancement (LGE), which may help assess the extent of inflammation and support risk evaluation.

Treatment with immunosuppressive therapy during hospitalization, especially corticosteroids and additional targeted agents in selected cases, was associated with improved survival free from heart transplantation or death. These data support the pivotal role of the early recognition of the disease and prompt initiation of appropriate anti-inflammatory therapy.

By analyzing data from a large international population, this study offers clearer information about presentation, prognosis, and treatment response in acute EM. These findings may help physicians refine early risk assessment, guide therapeutic decisions, and support the development of more personalized and effective treatment strategies in the future.

The figure below summarizes the main findings of the study.

Link to full article

Ammirati E et al. Circulation. 2026 Feb 6. doi: 10.1161/CIRCULATIONAHA.125.074797.
https://doi.org/10.1161/circulationaha.125.074797

Ammirati E, Palazzini M, Lehtonen J, Potena L, Mäyränpää MI, Rågback J, Foà A, Uribarri A, Thiele H, Vidal-Burdeus M, Freund A, Gustafsson F, Tschöpe C, Elsanhoury A, Ihle J, Rudi WS, Grabmaier U, Merlo M, Melenovský V, Weislova I, Jellinghaus S, Linke A, Baldovini C, Adorisio R, Kuchynka P, Paleček T, Krejčí J, Poloczková H, Caterino AL, Gilotra NA, Lovell JP, Macomb EP, Shih J, Hong K, Rossi VA, Ruschitzka F, Cavallini C, Riccini C, Kamal M, Huang F, Groh M, Gentile P, Garascia A, Lala A, Shimokawa H, Vandenbriele C, Sionis A, Schmidt M, Grosu A, Bollano E, Turco A, Crespo-Leiro MG, Couto-Mallon D, Cannatà A, Bromage DI, Narducci ML, Cicchitti V, Ianni U, De Luca L, Mistrulli R, Frea S, Raineri C, Schroeder JW, Arias AM, Emdin M, Corda M, Pasqualucci D, Greulich S, Gawaz M, Manuylova T, Martínez-Sellés M, Hernández Pérez FJ, Martín Centellas A, Dominguez F, Gaillet A, D’Alessandris N, Trankle C, Halushka MK, Moroni F, Abbate A, Basso C, Sinagra G, Veronese G, Camici PG, Adler ED, Bernasconi DP, Klingel K, Cooper LT Jr.

Natural History of Patients With Histologically Proven Acute Eosinophilic Myocarditis. Circulation. 2026 Feb 6. doi: 10.1161/CIRCULATIONAHA.125.074797. Epub ahead of print. PMID: 41645905

Prepared by Marco Merlo and Ruth Biller