Certain histologic findings can be helpful in the diagnosis of myocarditis.
Criteria for myocarditis:
(1) >= 14 leukocytes per square mm, focal or diffuse
(2) includes 0 to 4 macrophages per square mm
(3) includes T-cells (>= 7 per square mm)
Immunohistochemistry is sensitive for the detection of leukocytes. Usually a panel of stains is performed which may include:
(1) leukocyte common antigen (LCA, CD45)
(2) T-cell markers (CD3, CD4, CD8)
(3) B cell markers (CD20)
(4) monocytes (CD68)
Subtypes based on presence of or predominance:
(1) lymphocytic
(2) giant cell
(3) eosinophilic
Counting is often based on the microscopic field area.
number per square mm =
= (number per high power field) / (microscopic area of hpf in square mm)
Differential diagnosis:
(1) leukemia or malignant lymphoma
(2) inflammatory response to myocardial infarction
