FAQ on What an Autopsy Might Show
Written By Monte Willis MD, PhD, FASCP, FCAP
How is the diagnosis of myocarditis made on autopsy?
A: The diagnosis of myocarditis is not generally obvious by looking at the heart or other organs. Making the diagnosis first requires a high degree of clinical suspicion by the physicians taking care of the patient, the physicians and family requesting the autopsy, and by the physician performing the autopsy. Since there are a number of people on this team, it is critical that they understand the non-specific nature of myocarditis. They must also have a high degree of suspicion the myocarditis may be a cause of disease.
Myocarditis, or inflammation of the heart, may elicit characteristic electrical activity in the heart (seen by electrocardiography/ECG), elevated C-reactive protein levels (CRP) or increased erythrocyte sedimentation rate (ESR). Markers of cardiomyocyte damage such as elevated circulating troponin can be elevated (i.e. in the blood)1. ECG changes (heart monitor) indicative of myocarditis include diffuse T waves and saddle shaped ST-segment elevations, which can be seen in pericarditis as well (inflammation of the outer membrane of the heart) 1. Histological analysis of the heart tissue may reveal edema (swelling), inflammatory cells including lymphocytes and macrophages, and focal cell death of cardiomyocytes, which directly lead to the failure of the heart 1.
What does it mean to diagnose something by histology (or histological analysis)?
A: Many disease processes occurs on the microscopic level and cannot be seen by other means. In order to see what is going on in tissue, physicians will look at finely cut and stained tissue sections to identify the disease process going on. The disease process in myocarditis can only be definitively diagnosis by histological investigation of very small pieces of heart tissue. In severe cases the heart may be enlarged (dilated) and the ventricular (pumping) chambers may have thin walls.
How is myocarditis diagnosed histologically?
A: Using a microscope, thinly sliced sections of specially stained heart are looked at under high magnification. At this level, a physician can identify small inflammatory cells that are found in the heart that are causing damage to the heart itself. These cells include lymphocytes, monocytes and neutrophils and occasionally eosinophils, each with roles in killing infections, infected cells. These cells may also cross-react with normal (heart) cells to damage them as well. Cell death of the cardiomyocytes (the contracting heart cells) may or may not be seen.
How can infectious etiologies be tested for on autopsy?
A: In general, the heart looks pretty normal in patients with myocarditis by the naked eye. In general, clinical signs suggestive of myocarditis have to be present to focus a histological analysis of the heart, although it may be picked up on routine analysis. Symptoms in adults may be mild or severe, such as chest pain, rapid or abnormal heartbeat, shortness of breath, fluid retention in the lower legs, and fatigue. Children with myocarditis may have fever, difficult or rapid breathing, fainting, or discoloration of the skin.
There are different histologic patterns in the heart tissue, which may give physicians some insight into the etiology. For example, if lymophocytes are predominantly found, it might indicate a viral or autoimmune cause. If eosinophils are found, it might indicate a hypersensitivity myocarditis or hypereosinophilic syndrome. If granulomas are found, cardiac sarcoidosis or giant cell myocarditis may be the cause. If neutrophils predominate, bacterial, fungal, or early viral infection may be the cause. While these classifications of disease based on histology is complicated by the limited amount of tissue obtained from a biopsy in live patients, this is not an issue generally at autopsy. A presumptive diagnosis may be confirmed by indirect methods such as serology (looking for antibodies against specific infectious agents known to be able to cause myocarditis).
On autopsy, acute (recent onset) myocarditis is characterized by diffuse inflammatory cell infiltration by histology. Subacute myocarditis can manifest as dilation (enlargement) of the ventricles (which pumps the blood out of the heart), thin ventricular walls, and edema (fluid) in the tissues. In chronic myocarditis, irregular scarring with dilated chambers, thin (or thickened) walls may be present.
- Feldman AM, McNamara D. Myocarditis. The New England journal of medicine 2000;343:1388-98.