From the Guidelines
Lymphocytosis in a 12-month-old infant is most likely caused by a viral infection, as this is a common cause of elevated lymphocyte count in infants.
Possible Causes of Lymphocytosis
- Viral infections: Such as respiratory syncytial virus, influenza, or adenovirus, which are common in infants and can cause an increase in lymphocyte count 1.
- Bacterial infections: Although less common, bacterial infections such as pertussis or tuberculosis can also cause lymphocytosis.
- Immunodeficiency disorders: Such as severe combined immunodeficiency (SCID), which is a rare condition that can cause an abnormal immune response and elevated lymphocyte count 1.
Diagnostic Approach
A complete blood count (CBC) and differential count can help identify lymphocytosis, and further testing such as flow cytometry and immunoglobulin levels can help diagnose underlying conditions 1.
Management
Treatment of lymphocytosis depends on the underlying cause, and may include antiviral or antibacterial medications, as well as supportive care such as hydration and rest. In cases of immunodeficiency disorders, immunoglobulin replacement therapy and hematopoietic stem cell transplantation may be necessary 1.
From the Research
Causes of Lymphocytosis
The causes of lymphocytosis (elevated lymphocyte count) in a 12-month-old infant can be varied. Some possible causes include:
- Infectious diseases, such as infectious mononucleosis (IM) 2
- Reactive lymphocytosis, which is usually self-limiting and normalizes after cessation of the inflammatory stimulus 3
- Lymphoproliferative disorders, such as chronic lymphatic leukaemia (CLL) 4, 5
- Normal variations in lymphocyte count 6
Diagnostic Approach
To determine the cause of lymphocytosis, a thorough clinical review, including history, examination, and preliminary investigations (blood tests, blood film), is necessary 5. Further diagnostics may include:
- Heterophil antibody (HA) and Epstein-Barr virus (EBV) titers to rule out infectious mononucleosis 2
- Cytometry, bone marrow examinations, biopsies of other organs, and molecular analyses to differentiate between reactive and neoplastic conditions 3, 6
- Watch and wait strategy if the distinction between malignant lymphoproliferation and reactive lymphocytosis cannot be made immediately 3
Considerations in Infants
It is essential to note that the studies provided are mostly focused on adults or older children, and the causes and diagnostic approaches may differ in infants. However, the general principles of diagnostic evaluation and consideration of various causes, including infectious and neoplastic conditions, remain relevant 2, 3, 6, 4, 5.