Marked Neutrophilic Cerebrospinal Fluid Pleocytosis Following Intravenous Immunoglobulin Mimicking Bacterial Meningitis.

Intravenous immunoglobulin (IVIG) is an established therapy for immune-mediated neurological disorders and is generally well-tolerated, although rare neurological adverse effects have been reported. We describe a woman in her 40s treated with IVIG for suspected acute inflammatory demyelinating polyneuropathy following Campylobacter infection. Within 48 hours of therapy, she developed a headache and fever without meningism. Neuroimaging was unremarkable. Cerebrospinal fluid (CSF) analysis demonstrated marked pleocytosis with neutrophilic predominance, initially suggestive of bacterial meningitis. However, inflammatory markers and microbiological investigations were negative. Symptoms resolved rapidly following the discontinuation of IVIG without antimicrobial therapy. A diagnosis of IVIG-induced aseptic meningitis was made. This case highlights that IVIG can produce marked CSF pleocytosis mimicking bacterial meningitis and underscores the importance of clinical correlation to avoid unnecessary antimicrobial treatment.