Although the clinical diagnosis of meningitis is often supported by the presence of abnormal number of WBCs in the CSF (AKA pleocytosis), meningitis may be present despite its absence. Among viral causes of meningitis in adults, enteroviruses are associated with lower CSF WBC count compared to herpes simplex and varicella zoster, with some patients (~10%) having 0-2 WBC’s/mm31,2. Of interest, among children, parechovirus (formerly echovirus 22 and 23) meningitis is characterized by normal CSF findings3.
Though uncommon, bacterial meningitis without CSF pleocytosis has been reported among non-neutropenic adults, involving a variety of pathogens such as Neisseria meningitidis, Streptococcus pneumoniae, Hemophilus influenzae, Listeria monocytogenes, E. coli, and Proteus mirabilis4. Cryptococcal meninigitis may also be associated with normal CSF profile in 25% of patients with HIV infection5.
Thus, despite the absence of CSF pleocytosis, appropriate microbiological studies may still be necessary in some patients suspected of meningitis.
- Ihekwaba UK, Kudesia G, McKendrick MW. Clinical features of viral meningitis in adult:significant differences in cerebrospinal fluid findings among herpes simplex
- Dawood N, Desjobert E, Lumley J et al. Confirmed viral meningitis with normal CSF findings. BMJ Case Rep 2014. Doi:10.1136/bcr-2014-203733.
- Wolthers KC, Benschop KSM, Schinkel J, et al. Human parechovirus as an important viral cause of sepsis like illness and meningitis in young children. Clin Infect Dis 2008;47:358-63.
- Hase R, Hosokawa N, Yaegashi M, et al. Bacterial meningitis in the absence of cerebrospinal fluid pleocytosis: A case report and review of the literature. Can J Infect Dis Med Microbiol 2014;25:249:51.
- Darras-Joly C, Chevret S, Wolff M, et al. Cryptococcus neoformans infection in France: epidemiologic features of and early prognostic parameters for 76 patients who were infected with human immunodeficiency virus. Clin Infect Dis 1996;23:369-76.