Colour is clear and colourless, that is usually normal or viral meningitis. (In Bacterial meningitis the CSF looks turbid).
WBC = 850 ul. That indicates meningitis. (WBC to RBC ratio is more than 1:500, that excludes traumatic tap). However, count of 850 is not helpful in differentiating viral from bacterial meningitis. (CSF WBC in viral meningitis is usually < 1000 while CSF WBC for bacterial meningitis is usually > 500).
WBC differential however can help us in making this differentiation. In bacterial meningitis the predominant cells are the polymorphs. Here it is 99% monocytes that is usually viral (Fungal and TB meningitis also shows monocytes only in CSF however the count is usually less than 500).
With no bacteria seen on microscopy with the WBC count and differential that we see, this patient is most likely have viral meningitis.
Viral meningitis is usually associated with normal CSF glucose and CSF protein less than 1 g/L. This patient CSF glucose is low and CSF protein is high.
Viral meningitis is usually caused by enteroviruses. Meningitis due to these viruses is usually associated with normal CSF glucose and CSF protein < 1 g/L.
Meningitis due to HSV is usually associated with low CSF glucose and elevated CSF protein. PCR confirmed HSV meningitis.
It is important to consider HSV as it causes acute necrotising encephalitis. We should start acyclovir ASAP to those patients to limit the replication of the virus.
Next, why this patient has mild xanthochromia? The presence of high protein in the CSF can lead to falsely elevated bilirubin level.
High CSF protein levels can be caused by:
- Conditions where CSF circulation is impeded (spinal tumours)
- Meningeal inflammation (Purulent or TB meningitis and HSV)
- Increased Blood-Brain Barriers permeability (Encephalitis, Guillain-Barré syndrome).
- Local immunoglobulin production (Multiple sclerosis).
- The presence of pus or blood in the CSF.