Atypical lymphocytosis due to infections is classically seen in viral and chronic bacterial infections. A four year old boy with acute streptococcal infection presented at Al-Nahdha Hospital, Muscat, Oman, with follicular tonsillitis and bilateral cervical lymphadenitis. The blood film showed 33% atypical lymphocytes. Serologically, immunoglobulin M (IgM) antibodies were positive for cytomegalovirus, herpes simplex virus, and Epstein Barr virus, but the patient responded dramatically to antibiotics.
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Acute bacterial infections usually produce neutrophilic leucocytosis. Chronic bacterial and viral infections typically cause lymphocytosis. However, acute streptococcal infections can lead to atypical lymphocytosis as well as elicit false positive viral antibody results.
Atypical lymphocytes are shown here. These WBC’s are “atypical” because they are larger (more cytoplasm) and have nucleoli in their nuclei. The cytoplasm tends to be indented by surrounding RBC’s. Such atypical lymphocytes are often associated with infectious mononucleosis from Epstein-Barr virus (EBV) infection.
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Causes of Atypical Lymphocytosis
Lymphocytosis is a feature of infection, particularly in children. In the elderly, lymphoproliferative disorders, including chronic lymphocytic leukaemia and lymphomas, often present with lymphadenopathy and a lymphocytosis.
Causes of absolute lymphocytosis include:
- acute viral infections, such as infectious mononucleosis(glandular fever), hepatitis and Cytomegalovirus infection
- other acute infections such as pertussis
- some protozoal infections, such as toxoplasmosis and American trypanosomiasis (Chagas disease)
- chronic intracellular bacterial infections such as tuberculosis or brucellosis
- chronic lymphocytic leukemia
- acute lymphoblastic leukemia
- lymphoma
- post-splenectomy state
- smoking
Causes of relative lymphocytosis include: age less than 2 years; acute viral infections; connective tissue diseases, thyrotoxicosis, Addison’s disease, and splenomegaly with splenic sequestration of granulocytes.
read more about Signs and Symptoms of Lymphocytosis
Atypical lymphocytosis, viral and bacterial illnesses
Atypical lymphocytosis is most commonly attributed to viral and bacterial illnesses. It can also be a result of some types of autoimmune disorders. Immunizations, drug reactions, and radiation or chemotherapy treatments can also cause elevated lymphocytes to become atypical.
A person of any age can develop atypical lymphocytosis, but there are some people who are more susceptible than others. Children under the age of two do not have a developed immune system. Adults with connective tissue diseases or otherwise weakened immune systems may have an increase of atypical lymphocytes. Patients with acute or chronic leukemia may also have an occurrence of atypical lymphocyte increase.
