The following is a CSF sample from a 56-year-old woman with severe rheumatoid arthritis who has presented with fever, malaise and altered mental state
Parameter |
Value |
Normal Range |
Cell count |
75 cells / mm3* |
0 – 5 |
(90% lymphocytes) |
||
Protein |
890 mg/L* |
170 – 550 |
Glucose |
2.0 mmol/L* |
2.8 – 4.5 |
Gram stain |
Negative |
Describe 4 further tests you would perform upon the CSF to establish an infective cause.
College Answer
- Herpes Simplex PCR
- Mycobacterium Tuberculosis PCR
- Mycobacterial Stain and Cultures
- India Ink Stain, Cryptococcal Ag
- Fungal cultures
- Bacterial PCR
Discussion
The question is really asking, "what pathogens can cause a meningitis, but wont be picked up on a routine gram stain?" The answer is "anything that is not a classical bacterium". This is what one might call "aseptic meningitis". LITFL has an excellent summary of this topic.
The list contains the following bugs:
- Mycobacteria:
- M.tuberculosis
- Fungi:
- Cryptococcus neoformans
- Viruses:
- HSV
- VZV
- CMV
- HIV
- Enterovirus
- Random:
- Treponema pallidum
- Borrelia burgdorferi (Lyme disease)
Additionally, one might wish to consider non-infectious causes, such as lymphoma, vasculitis, or drug-induced meningitis (eg. due to cotrimoxazole or azathiaprine)
Interestingly, the most likely causes of CSF lymphocytosis are the common meningitis pathogens -S.pneumoniae, H.influenzae and N.meningitides.
The richness of this pathology is serenaded in a dedicated chapter on meningitis.
References
Powers, William J. "Cerebrospinal fluid lymphocytosis in acute bacterial meningitis." The American journal of medicine 79.2 (1985): 216-220.