A Red Herring in the Cerebrospinal Fluid: Xanthochromia Due to Mixed Etiology in the Absence of Subarachnoid Hemorrhage

Xanthochromia in cerebrospinal fluid (CSF) is most commonly associated with subarachnoid hemorrhage (SAH), but other etiologies must be considered when initial imaging is unremarkable. We present the case of a 50-year-old woman with a sudden, severe headache. Computed tomography (CT) of the head was normal, but lumbar puncture revealed xanthochromia, elevated CSF protein (139.5 mg/dL), and no red or white blood cells. Varicella zoster virus (VZV) was detected by CSF polymerase chain reaction (PCR), and MRI demonstrated chronic cervicomedullary stenosis without evidence of hemorrhage or encephalitis. The patient was treated empirically with intravenous acyclovir and fully recovered. The findings suggest a mixed etiology for xanthochromia involving partial mechanical obstruction of CSF flow and a subclinical viral process. This case highlights the importance of considering infectious, inflammatory, and structural causes in the differential diagnosis of xanthochromia when SAH is excluded.