Histological Features
Histologically, infectious mononucleosis is identified by specific changes in the blood and lymphoid tissues. A hallmark of the disease is the presence of
atypical lymphocytes, which are often larger than normal lymphocytes with abundant cytoplasm and irregular, indented nuclei.
Peripheral Blood Smear
A peripheral blood smear in a patient with infectious mononucleosis reveals an increased number of atypical lymphocytes. These cells are sometimes referred to as "Downey cells." The blood smear may also show lymphocytosis, which is an increased number of
lymphocytes in the blood.
Lymph Node Histology
In lymph nodes, hyperplasia of paracortical areas is commonly observed. This hyperplasia is due to the proliferation of
T-lymphocytes in response to the viral infection. The lymph nodes are often enlarged and may exhibit a mottled appearance.
Spleen and Liver Involvement
The spleen is frequently enlarged (splenomegaly) in cases of infectious mononucleosis. Histologically, the spleen shows lymphoid hyperplasia and sometimes congestion. The liver may also be affected, showing signs of
hepatitis with focal necrosis and inflammation.
Immunohistochemistry
Immunohistochemical staining can be used to differentiate between various cell types and identify viral antigens. For instance, markers such as CD3 and CD8 can help identify T-cells, while CD20 can identify B-cells. EBV-specific antigens can also be detected using specific antibodies.
Diagnostic Criteria
The diagnosis of infectious mononucleosis is often based on a combination of clinical presentation and laboratory findings. The presence of atypical lymphocytes in a peripheral blood smear, along with positive
heterophile antibody tests (such as the Monospot test), are commonly used diagnostic criteria. Serological tests for EBV-specific antibodies can also confirm the diagnosis.
Complications
While infectious mononucleosis is generally self-limiting, it can lead to complications such as splenic rupture, airway obstruction, and secondary infections. In rare cases, the disease can cause
hemolytic anemia or thrombocytopenia.
Treatment and Prognosis
There is no specific antiviral treatment for infectious mononucleosis. Management primarily involves supportive care, including rest, hydration, and analgesics for pain and fever. Most patients recover fully within a few weeks to months, although fatigue can persist longer in some cases.
