Loeffler endocarditis is a restricive cardiomyopathy which is characterized by fibrous thickening of the endocardium, leading to apical obliteration and restrictive cardiomyopathy, resulting in heart failure, thromboembolic events, or atrial fibrillation. Loeffler endocarditis is caused by eosinophilic states which may include hypereosinophilic syndrome, eosinophilic leukemia, carcinoma, lymphoma, drug reactions or parasites, as reported in multiple case series.
Pathophysiologically, the fibrotic stage of Loeffler endocarditis is very similar to the disease entity described as endomyocardial fibrosis, which is indolent in comparison to Loeffler endocarditis. The tropical form of endomyocardial fibrosis is associated with eosinophilia, a common finding in Loeffler endocarditis. Morphologic abnormalities of eosinophils have been noted in patients with Loeffler endocarditis, suggesting that these eosinophils were mature or stimulated. The intracytoplasmic granular content of activated eosinophils is thought to be responsible for the toxic damage to the heart, as reported by Tai and associates.