Curriculum · Neurology
Structured approach to the patient with suspected CNS infection
What it is
When a patient with a suspected CNS infection is approached, the focus rests on three things:
- Age and risk factors.
- The symptoms and their duration.
- The CSF findings.
These three are what the approach is built on, and they are taken together rather than one at a time. What the CSF analysis will tell you is whether the picture is bacterial or viral, on 4 parameters. What it will not tell you is the type of bacteria or virus; that comes from the history and the CSF culture. Typical CSF findings in patients with viral and bacterial meningitis, viral first and bacterial second:
- Opening pressure: 250 mm H2O or below; 200-500 mm H2O.
- Leukocyte count: 50-1000/uL; 1000-5000/uL.
- Leukocyte predominance: lymphocytes; neutrophils.
- Glucose level: above 45 mg/dL, that is 2.5 mmol/L; below 40 mg/dL, that is 2.2 mmol/L.
- Protein level: below 200 mg/dL, that is 2000 mg/L; 100-500 mg/dL, that is 1000-5000 mg/L.
- Gram stain: negative; positive in 60%-90%.
- Culture: negative; positive in 70%-85%.
The rows do not carry the same weight. Leukocyte count is marked important and set first, and the note beside its viral value reads if low, exclude bacteria. Protein level is marked important and set second, with its viral value underlined. Glucose level is marked as not that specific.