Answer: Giant cell myocarditis

Histology: The explanted heart was remarkable for an intense diffuse lymphocytic infiltrate with numerous associated multinucleated giant cells. Numerous myocyte necroses were present, and in some areas the myocardium was completely replaced with scar tissue.

Discussion: Idiopathic giant cell myocarditis is a rapidly progressive form of myocarditis characterized by an intense inflammatory cell infiltrate with multinucleated numerous giant cells. The prognosis is extremely poor. In one series the 5-year transplant free survival after diagnosis was only 22%. Even after transplantation, the disease can recur in the patient’s new heart. The major entity to consider in the differential diagnosis is cardiac sarcoid. Patients with cardiac sarcoid are more often African-American and present with heart block more frequently than do patients with giant cell myocarditis. Well-formed granulomas and extra-cardiac disease (particularly mediastinal lymphadenopathy) should both suggest cardiac sarcoid.

Reference(s):
– Okura et al., A clinical and histopathologic comparison of cardiac sarcoidosis and idiopathic giant cell myocarditis. J Am Coll Cardiol., 2003; 41: 322-329.
– Scott et al., Recurrence of giant cell myocarditis in cardiac allograft. J Heart Transplant 2001; 20:375-380.
– Cooper et al., Idiopathic giant cell myocarditis- natural history and treatment. N Engl J Med 1997; 336: 1860-1866.