A 17-year-old right-handed girl with a history of catamenial headaches presented with a 1-week history of severe holocranial headache, nausea, vomiting, and photophobia following a viral prodrome with arthralgia. Initial evaluation was unremarkable. She re-presented with persistent, now positional headache worse when supine, nuchal rigidity, vertigo, horizontal and vertical nystagmus, lateral gaze restriction without papilledema. Brain MRI revealed ventriculitis, choroid plexitis, and meningitis with FLAIR hyperintensity in the parieto-occipital and cerebellar regions, leptomeningeal and oculomotor nerve enhancementCSF revealed lymphocytic pleocytosis (WBC 1200), elevated protein, and hypoglycorrhachia. Atypical cells in CSF raised concern for malignancy but cytology favored a reactive process. Broad infectious and autoimmune testing, including meningoencephalitis panel, EBV, HSV, and mNGS were negative. CSF Lyme IgM and IgG were elevated but confirmed negative on serum and CSF Western blot. Autoimmune workup showed elevated CSF ACE and inflammatory cytokines (IL-2, IL-6, IL-10). Imaging ruled out systemic sarcoidosis.
Further history revealed rodent exposure at workplace. LCMV serologies were positive in both serum and CSF, confirming neuroinvasive LCMV. The patient was treated with doxycycline, symptoms resolved except for mild residual headache on discharge.