Differential Diagnoses of Eosinophilic Myocarditis in Endomyocardial Biopsies and Accompanying Challenges

Parasitic infections, hypersensitivity myocarditis, and hypereosinophilic syndrome are collectively regarded as eosinophilic myocarditis. Endomyocardial biopsy is the gold standard for the diagnosis in such types of myocarditis, particularly in patients with unexplained heart failure or ventricular arrhythmias. A number of pitfalls should be remembered by the pathologist, namely a focal lesion in the left side of the heart, which is missed if the biopsy is taken from the right ventricle. Endocardial fibrosis can be a non-specific finding or it may represent a specific pathology such as hypereosinophilic syndrome. In order to overcome this problem, adequate and deep sampling from the myocardium would facilitate its identification. Finally, if superficial sampling of the myocardium is done, the pathologist may only observe pieces of thrombi rather than the myocardium proper. Therefore, one is advised to look for even minute collections of inflammatory cells, including eosinophils in the mural thrombi.