Clinical Reasoning: A 26-Year-Old Woman With Headache and Eosinophilia.

Headache accompanied by eosinophilia in blood or CSF presents a complex clinical challenge. We present a case of a 26-year-old woman with headache, peripheral eosinophilia with meningeal enhancement, and intracranial vasculopathy on imaging. This case illustrates a systematic approach to a patient with meningitis, peripheral eosinophilia, and cerebral vasculitis, which includes comprehensive clinical history taking and appropriate investigative workup to differentiate between infectious and noninfectious causes and timely tissue sampling to conclusively determine the causative agent.