B. Viral meningitis – Explanation
The CSF lymphocytosis combined with a glucose greater than half the serum level points towards a
viral meningitis. TB meningitis is associated with a low CSF glucose
Meningitis: CSF analysis
The table below summarises the characteristic cerebrospinal fluid (CSF) findings in meningitis:
| Bacterial | Viral | Tuberculous | |
| Appearance | Cloudy | Clear/cloudy | Fibrin web |
| Glucose | Low (< 1/2 plasma) | Normal* | Low (< 1/2 plasma) |
| Protein | High (> 1 g/l) | Normal/raised | High (> 1 g/l) |
| White cells | 10 – 5,000 polymorphs/mm3 |
15 – 1,000 lymphocytes/mm3 |
10 – 1,000 lymphocytes/mm3 |
The Ziehl-Neelsen stain is only 20% sensitive in the detection of tuberculous meningitis and
therefore PCR is sometimes used (sensitivity = 75%)
*mumps is unusual in being associated with a low glucose level in a proportion of cases. A low
glucose may also be seen in herpes encephalitis
Serum glucose 4.9 mmol/l
Lumbar puncture reveals:
Opening pressure 14 cmCSF
Appearance Cloudy
Glucose 1.7 mmol/l
Protein 1.9 g/l
White cells 900 / mm3 (90% polymorphs)
