Endomyocardial biopsy results are integral for diagnosis and management of myocarditis. Current diagnostic classifications of myocarditis are based on the microscopic and immunochemical characterization of inflammation do not include monocyte/macrophage-predominant (i.e. “histiocytic”) myocarditis as a histologic subtype.
Endomyocardial biopsies from 6 patients with sudden heart failure were reviewed by 3 cardiac pathologists. Routine stains and immunostains to identify T cells and monocytes/macrophages, complement C4d, and endothelium were applied. Electron microscopy was performed in 2 cases.
The 6 patients included 2 with diagnoses of systemic lupus erythematosus (SLE) and 4 without known disease. Microscopy showed space-occupying inflammation in 2 cases and interstitial inflammation in 4. No giant cell myocarditis or eosinophilic myocarditis was found. Immunostains showed infiltration predominantly by macrophages and/or monocytes with markedly fewer T cells. In 4 of 6 cases necrotic cells were immunopositive for complement C4d. Monocytes we identified immunochemically within the microvasculature in 5 cases and by electron microscopy in 2. Patients with SLE had microvascular C4d positivity or interstitial/sarcolemmal staining. Clinical outcomes ranged from spontaneous resolution to persistent heart failure requiring an internal cardioverter/defibrillator.
(1) Heart failure with CD68 predominant inflammation (“histiocytic” myocardial inflammatory disease, HMID) occurs with variable clinical presentation and outcome; (2) HMID may be primary or secondary; (3) some cases of HMID show features suggestive of antibody and/or complement mediated myocardial injury, and (4) HMID is a diagnosis distinct from those in classification systems currently in use.