Aretz et al reported histopathologic criteria for the diagnosis of myocarditis in endomyocardial biopsies. These can help standardize the diagnosis and reporting of biopsy findings. The criteria were developed at a meeting of the American College of Cardiology in Dallas, Texas.


Histopathologic features of myocarditis - all of the following:

(1) inflammatory infiltrate of the myocardium

(2) necrosis and/or degeneration of adjacent myocytes (degeneration may take the form of cytoplasmic vacuolization, irregular cellular outlines or cellular disruption) in conjunction with the inflammatory cell infiltrate

(3) exclusion of other causes, especially ischemic damage


Terminology to be used on the first endomyocardial biopsy:

(1) definite myocarditis with or without fibrosis (when all of the criteria are present)

(2) borderline myocarditis with or without fibrosis (equivocal, when some of the criteria are present)

(3) negative for myocarditis (when none of the criteria are present)


Terminology for subsequent biopsies:

(1) persistent or ongoing myocarditis with or without fibrosis

(2) resolving or healing myocarditis with or without fibrosis

(3) resolved or healed myocarditis with or without fibrosis


If a previous biopsy showed healed myocarditis and the current biopsy shows definite or borderline myocarditis, then the tissue is interpreted as a first biopsy (? recurrent myocarditis?).


Description of histologic features in the biopsy:

(1) type of inflammatory infiltrate: lymphocytic, eosinophilic, neutrophilic, granulomatous, giant cell, or mixed

(2) intensity of inflammatory infiltrate: none, mild, moderate or severe

(3) distribution of inflammatory infiltrate: focal, confluent or diffuse

(4) amount of fibrosis: none, mild, moderate or severe

(5) distribution of fibrosis: focal, confluent, or diffuse

(6) anatomic distribution of fibrosis: endocardial, replacement, interstitial

(7) presence and type of micro-organisms (viral inclusion, parasite, other)


Differential diagnosis for myocarditis:

(1) ischemic change associated with coronary artery disease

(2) biopsy of previous biopsy site

(3) tissue artifact

(4) myocarditis associated with vasopressor agents

(5) myocarditis secondary to other drugs

(6) leukemic or lymphomatous infiltrate

(7) nonspecific inflammation in idiopathic, dilated cardiomyopathy


Reasons for discrepancy between pathologic and clinical diagnosis:

(1) overdiagnosis by clinician

(2) misdiagnosis by pathologist (over or under interpretation of findings)

(3) focal disease missed on random biopsy (risk reduced by taking multiple biopsies)

(4) biopsy done during healing or healed phase when inflammation is reduced


Indications for rebiopsy:

(1) discrepancy between clinical and pathologic diagnosis

(2) diagnosis of borderline myocarditis

(3) inadequate specimen


To read more or access our algorithms and calculators, please log in or register.