Polyclonal B-cell lymphocytosis mimicking malignant lymphoma in a newborn

Area of Science:

• Pediatric Hematology
• Immunology
• Neonatal Medicine

Background:

• Neonatal fever and lymphocytosis can mimic serious conditions like leukemia.
• Distinguishing benign reactive lymphocytosis from malignancy is crucial in newborns.

Observation:

• A 17-day-old infant presented with fever and atypical peripheral blood lymphocytes.
• These lymphocytes exhibited large size, irregular nuclei, and immature features, raising concern for malignant lymphoma.
• Initial presentation suggested a potential leukemic phase of lymphoma.

Findings:

• Immunophenotyping identified the lymphocytes as CD19-positive B cells expressing both kappa and lambda light chains.
• Molecular studies confirmed a polyclonal immunoglobulin heavy-chain gene rearrangement, indicating a non-clonal origin.
• Cytogenetic analysis revealed a normal karyotype, and infectious workup was negative.

Implications:

• This case highlights the importance of comprehensive immunophenotypic and molecular analysis in diagnosing neonatal lymphocytosis.
• It demonstrates that unusual lymphocyte morphology in neonates can represent a benign, self-limiting condition.
• Accurate diagnosis prevents unnecessary aggressive treatment for conditions like lymphoma.