Staining with two observational methods for the diagnosis of tuberculous meningitis

Ziehl-Neelsen (Z-N) staining of cerebrospinal fluid (CSF) for acid-fast bacilli (AFB) is the cornerstone of the laboratory diagnosis of tuberculous meningitis (TBM). However, the sensitivity of conventional Z-N staining for the detection of AFB in CSF specimens is suboptimal. The present study aimed to compare the practicality of modified Z-N staining with light microscopy and fluorescence microscopy in the same smear without auramine O. A total of 155 patients with 223 CSF specimens were enrolled and grouped according to the uniform case definition. The smears of each CSF specimen were subjected to modified Z-N staining and then observed using a light microscope under transmitted light and under fluorescence with a green-excitation wavelength in the same microscopic field. The results for different groups, inspection times, and prior to and following treatment were compared. Results indicated that the fuchsin-stained AFB were visible as bright orange-red fluorescing rods under fluorescence, or as red, lightly curved rods under transmitted light. The sensitivity of fluorescence microscopy was 96.2% while that of light microscopy was 84.6%. The positive rate of fluorescence microscopy was 79.2% prior to treatment compared with 61.7% post-treatment. In the same microscopic field, a greater number of AFB were observed using fluorescence compared with transmitted light, and AFB that were not visible under transmitted light were clearly observed under fluorescence. Furthermore, transmitted light and fluorescence could be interchanged directly when equivocal smears were encountered. The combination of modified Z-N staining and fluorescence microscopy without auramine O is sensitive and convenient for the diagnosis of TBM.