Eosinophilic meningitis caused by primary angiitis of the central nervous system.

Eosinophilic meningitis is defined as the presence of 10 eosinophils/mm(3) in the cerebrospinal fluid (CSF) or eosinophils accounting for more than 10% of CSF leukocytes. A 76-year-old man who developed cognitive dysfunction and consciousness disturbance had eosinophilic meningitis (his CSF contained 19.0% eosinophils). Because the etiology was unknown, we performed a brain biopsy. The pathological findings showed inflammatory infiltration in the small-sized arteries of the meninges. The patient was ultimately diagnosed as having primary angiitis of the central nervous system (PACNS). Eosinophilic meningitis occurring in a patient with PACNS is extremely rare, and this is the first report of this condition in Japan.