An 18-year-old man presents to hospital with fever, increasing confusion, and aphasia. A CT
scan of the head is unremarkable. EEG shows temporal complexes and patterns of slowing. A
lumbar puncture is performed. Cerebral spinal fluid (CSF) findings are as follows:
Glucose: 70 mg/dL (normal range 50-80)
Protein: 75 mg/dL (normal range 15-60)
WBC: 220 cells/mm3
; lymphocyte predominance
RBC: 45 cells/mm3
Opening pressure: 180 mm H2O
Which of the following is the most likely diagnosis?
- A) Flavivirus
- B) Rhinovirus
- C) Echovirus
- D) Herpes simplex virus (HSV)
- E) Hanta virus
0 voters
EXP:
Opening pressure
• 10-100 mm H2O in young children; 60 to 200 mm H2O age >8; up to 250 mm H2O in obesity.1
• Fungal opening pressure increases proportional to fungal burden.2, 3 Even though ↑ opening
pressure is not specific for fungal meningitis, this association is HY on the USMLE.
• Opening pressure in HSV encephalitis is usually normal or increased.4 • In TB, opening pressure is ↑ roughly half the time.5
• In bacterial meningitis, opening pressure is >200 mm H2O in 90% of cases and >500 mm H2O in
15% of cases.6
• In viral, opening pressure is usually normal.7
Red blood cells (RBCs)
• Normal CSF should not have RBCs.7
• Unusual finding in CSF infections,7 and not characteristic of echovirus aseptic meningitis.8
• Presence of RBCs (>4-49/mm3
) in an infective setting is highly characteristic of HSV
encephalitis.9, 10
WBC count
• Normal range is 0-5/mm3
.
11
• >1,000 per mm3 in bacterial and <100 per mm3 in viral.7
• 10-500 cells/mm3 in fungal.12
• Usually 100-500 cells/mm3 in tuberculosis13, although other studies have shown means of 71
cells/mm3
.
14
• HSV usually ranges >100-250 cells/mm3
.
15
WBC type
• Normal CSF has mononuclear predominance at 0-5/mm3
.
11
• Neutrophils predominate in bacterial meningitis.7
• Lymphocytes predominate in viral, fungal, tubercular, and herpetic.7, 13, 15
Protein
• Normal range is 15-60 mg/dL.11
• Bacterial is usually 100-500 mg/dL.16
• Viral is usually <95 mg/dL.17
• Fungal is usually 20-150 mg/dL.18
• TB is usually 100-500 mg/dL.13
• For HSV, roughly half of patients are 60-100 mg/dL of protein; the other half has >100 mg/dL.19
Glucose
• Normal range is 50-80 mg/dL.7
• Bacterial is <40 mg/dL in 60% of patients.20
• Normal for viral.20
• Decreased in fungal and tuberculous meningitis.21
• Normal or decreased in HSV.22, 23
Meningitis is an infection of the meninges, the tissue membranes surrounding the brain and spinal
cord. Encephalitis is inflammation of the brain parenchyma itself