Definition
• A rare, frequently fatal inflammatory disorder of cardiac muscle of unknown origin, characterized by widespread giant cells, chronic inflammation, and degeneration and necrosis of myocardial fibers
Clinical features
Epidemiology
• Uncommon disorder that typically affects young to middle-aged adults; slight male preponderance
Presentation
• Usually previously healthy patients present with a history and symptoms characteristic of a flulike syndrome
• Congestive heart failure and ventricular tachycardia are the most common clinical manifestations
Prognosis and treatment
• Compared with the more commonly encountered lymphocytic myocarditis, giant cell myocarditis is more aggressive and is associated with greater mortality
• Tends to follow a rapidly deteriorating course unless immunosuppressive therapy is instituted or heart transplantation is performed
• The median survival rate from onset of symptoms until time of death or transplantation is 5.5 months
Pathology
Histology
• Diffuse intramyocardial infiltrate consisting of lymphocytes and macrophages with multinucleated giant cells
• Eosinophils are a common component of the inflammatory reaction
• The hallmark finding, the giant cells, represent fused epithelioid cells, usually 40 to 50 μm in diameter with large cytoplasmic mass containing greater than 20 nuclei, usually of the Langhans type
• Peripheral fibrosis may be present, perhaps reflecting the chronicity of the process
• Geographical areas of myocyte damage or necrosis are evident on low magnification
Immunopathology/special stains
• Not contributory
Main differential diagnoses
• Cardiac sarcoidosis
• Characterized by well-formed granulomas and fibrosis with few or no eosinophils
• Myocyte necrosis is usually absent
• Rarely seen as isolated cardiac involvement; lymph node or lung involvement almost always present
• Infectious granulomatous diseases
• Myocardial involvement is rarely isolated
• Giant cells and granulomas can be seen in tuberculosis, cryptococcosis, syphilis, or measles myocarditis
• Special stains may demonstrate visible microorganisms
• Rheumatic myocarditis
• Aschoff granulomas with giant cells often show central fibrinoid necrosis surrounded by a collection of lymphocytes, plasma cells, and macrophages
• Most commonly located in the endocardium of the atria and the perivascular spaces of the ventricles
• Foreign body reaction
• Birefringent material under polarized light
• Myocardial reaction to pacemaker leads and cardiac assist devices at the device–tissue interface
Fig 1 Giant cell myocarditis. Endomyocardial biopsy fragments showing dense diffuse infiltrate of lymphocytes and macrophages.
Fig 2 Giant cell myocarditis. Multinucleated giant cells and lymphocytes are present in significant numbers.
Fig 3 Giant cell myocarditis. Several eosinophils are intermixed with lymphocytes and giant cells.