This endomyocardial biopsy was taken from a 46-year-old man with recent-onset arrhythmias, dyspnea, and fatigue.
The histopathology shows myocytes involved by a lymphocytic inflammatory process causing multifocal myocyte damage. The appearance is diagnostic of an active lymphocytic myocarditis.
The diagnosis of active myocarditis based on the Dallas criteria, which requires inflammation of the myocardium with myocyte injury/damage that is not characteristic of ischemic injury.
Commonly accepted criteria for myocyte injury include lymphocytic “scalloping” of the sarcolemmic border (see arrows in photo), loss of cross-striations, and hypereosinophilia of the myocyte. If you have inflammation in the absence of myocyte damage, the proper diagnostic terminology is “borderline [inflammation type, e.g. lymphocytic] myocarditis”.
With regard to the differential diagnosis, borderline [lymphocytic] myocarditis shows the relevant inflammation, but without myocyte damage. The distinction can be exceptionally challenging at times.
Sarcoidosis is typified by tight, non-necrotizing granulomatous inflammation. The image shows a predominance of lymphocytic inflammation, without granuloma. It’s been loosely associated with Propionibacterium.
Giant cell myocarditis (GCM) has both giant cells (as the name implies) as well as eosinophils. The cause of GCM is unknown. Roughly 1/5 of individuals have an underlying autoimmune disease, making this a compelling association.
Myocardial infarctions may look different depending on the age of the lesion, but most commonly show neutrophilic inflammation, followed by macrophages, and fibroblasts. Lymphocytes aren’t a predominate part of the picture in this disease process.