Importance of classifying polymorphonuclear cells in cerebrospinal fluid by Samson staining: Four case reports of eosinophilic meningitis

Abstract

Cerebrospinal fluid (CSF) is often examined for the differential diagnosis of meningitis. In the laboratory, we count the white blood cell number and differentiate between mononuclear and polymorphonuclear cells by Samson staining. The increase in the number of polymorphonuclear cells mainly suggests bacterial meningitis; however, the percent increase in the number of eosinophils in CSF is rarely investigated, which is indicative of eosinophilic meningitis. Eosinophilic meningitis is a rare disease and is usually caused by parasitic infection. Pathogenetic factors other than infection, such as intraventricular shunt malfunction, however, can also cause this disease. Here, we present 4 case reports of eosinophilic meningitis, which was suspected on the basis of cytological analysis using Samson staining in the examination of CSF. Although eosinophilic meningitis is diagnosed when the percentage of eosinophils is over 8% of the total CSF white blood cell count determined by May-Giemsa staining, the examination by Samson staining has an advantage because it is easy and fast. Therefore, the cases presented in this report suggest that the classification of polymorphonuclear cells by Samson staining is useful for the differential diagnosis of meningitis.