Atypical Bilobed Lymphocytes in CSF: Diagnostic Insights into Varicella Zoster Virus Meningitis and Herpes Zoster with Temporal Presentations.

Background: Varicella-zoster virus (VZV) is a known cause of viral meningitis, which can occur with or without the hallmark vesicular rash. While atypical lymphocytes are commonly described in peripheral blood during primary VZV infection, their presence in cerebrospinal fluid (CSF) during VZV reactivation is rarely reported. Case Presentation: We describe two cases of VZV meningitis in immunocompromised young adults with atypical lymphocytes identified in the CSF. The first case involved a 19-year-old man with HIV who presented with meningitis symptoms, followed by the appearance of a dermatomal rash three days after initiation of acyclovir, consistent with herpes zoster. The second case involved a 21-year-old woman with systemic lupus erythematosus who presented with a vesicular rash and subsequent headache. In both cases, CSF analysis revealed mononuclear pleocytosis, mildly elevated protein, and the presence of bilobed or binucleated monocytoid lymphocytes on Wright's stain. CSF polymerase chain reaction confirmed VZV infection, and both patients recovered fully following intravenous acyclovir treatment. Conclusion: These cases highlight the diagnostic value of identifying atypical lymphocytes distinct from Mollaret's cells-specifically bilobed or binucleated monocytoid lymphocytes in CSF cytology. Recognizing these distinct morphological features can aid in differentiating VZV meningitis from other viral etiologies. Although previously associated with primary VZV infection, such cytological findings may also occur in reactivation and should prompt consideration of VZV as an etiology, even in the absence of cutaneous lesions. Early recognition facilitates timely antiviral therapy and favorable clinical outcomes.