Loeffler Endo(myo)carditis: Clinical Characteristics and Outcomes from a Tertiary Center Case Series

Background: Loeffler endocarditis is a rare cardiac condition characterized by myocardial infiltration with eosinophilic leukocytes, resulting in progressive cardiac dysfunction. Its low incidence and variable clinical presentations contribute to frequent misdiagnosis. Early identification is crucial to prevent progression to an irreversible restrictive phenotype. Due to its rarity, only small case series exist to evaluate its presentation, therapeutic strategies, and prognosis.
Methods: In this study, we retrospectively analyzed clinical presentation, laboratory findings, multimodal imaging, treatment and outcomes in a cohort of 16 patients diagnosed with Loeffler endo(myo)carditis between 2017 and 2024 at a tertiary high volume heart center.

Results: The median age was 44 years (range 13-69 years), with a predominance of male patients (n=12; 75%). Dyspnoea was the most common presenting symptom (n=10; 62.5%), while peripheral eosinophilia was observed in only 43.8% (n=7) of patients. The median left ventricular ejection fraction (LVEF) at presentation was 48%. Mean NT-pro-BNP at the time of diagnosis was 5210 ng/l. Cardiac magnetic resonance (CMR) imaging showed a predominance of subepicardial late gadolinium enhancement (LGE) in 85% of patients with available CMR data, though epicardial LGE was also seen in 46%. Left ventricular thrombi were found in 43% of cases. Based on this data we propose the diagnostic algorithm shown in Figure 1.
Treatment primarily consisted of corticosteroids (mean starting dose 86 mg, range 30-200 mg or 1.1 mg/kg as proposed by the WHO consensus document on eosinophilic disorders) and anticoagulation, administered to 87% of patients. All patients received beta-blockers and the majority additionally received RAAS inhibitors and aldosterone antagonists. Under therapy, LVEF remained stable, but NT-pro-BNP improved in 89% of cases. Where a thrombus was present, it resolved with treatment in all instances, and LGE extent decreased in 50% of patients. One patient experienced cardiac arrest due to ventricular fibrillation at the index hospitalization. No malignant arrhythmias were detected during follow-up. There were no deaths during the evaluation period of median 26 months (range 0 to 153 months), though one patient required cardiac transplantation.

Conclusion: The current findings suggest that timely diagnosis and treatment can significantly improve outcomes in Loeffler endo(myo)carditis. Multicenter trials and registries are needed to better understand the optimal management and prognosis of this rare condition.

Figure 1: Proposed diagnostic algorithm