Myocarditis - Lymphocytic
The diagnosis of myocarditis requires the presence of an inflammatory infiltrate as well as myocyte dropout, necrosis or degenerative changes. In this case of viral myocarditis, the infiltrate is predominantly lymphocytic.
This photo shows an extensive lymphocytic infiltrate along with myocyte dropout and necrosis. Lymphocytic myocarditis is usually secondary to viral infection; adenovirus and coxsackie are the most commonly involved viruses.
Myocarditis presents a wide clinical spectrum from sudden cardiac death to an asymptomatic state. Arrhythmias, heart block, failure, fever, chest pain, and non-specific ECG changes are all possible as presenting symptoms or findings. Primary myocarditis refers to myocardial inflammation in cases in which the primary injury is located within the myocardium or, at least, the myocardium is the major focus of infection. Known causes of primary myocarditis are cardiotoxic drugs, radiation, and infectious agents including viruses, bacteria, fungi, protozoa, and helminths. Infectious primary myocarditis can be acquired via the blood stream or by continuity with infection elsewhere. Viral myocarditis is usually a disease of children and young adults. With the immunosuppressed being especially vulnerable. RNA and DNA viruses have been associated with myocarditis. Enteroviruses, especially Coxsackie B, have been thought to be the most common cause. They have also been implicated in dilated cardiomyopathy in some of those who survive the initial episode of myocarditis. The list of viral agents less frequently causing myocarditis is long. It includes echoviruses, influenza, the viruses causing childhood exanthems, RSV, lymphocytic choriomeningitis virus, CMV, EBV, adenovirus and hepatitis B virus. Viral identification by PCR has been applied to endomyocardial biopsy tissue as well as to postmortem tissue. Previously thought to be a rare cause of myocarditis, the adenovirus is now recognized as a prominent player. In one series of autopsy cases of myocarditis, a viral genome could be identified by PCR in 59%. Of those positive cases, 53% and 35% were positive for adenovirus and enterovirus, respectively.