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