A 16-year-old girl has had increasing frontal headaches over the past four days that have
become unbearable and associated with fevers and rigor. She reports having vomited once, as well
as neck pain/stiffness and photophobia. A lumbar puncture is performed. Her cerebral spinal fluid
(CSF) findings are as follows:
Glucose: 55 mg/dL (normal range 50-80)
Protein: 65 mg/dL (normal range 15-60)
WBC: 90 cells/mm3
; lymphocyte predominance
RBC: 0-1 cells/mm3
Opening pressure: 180 mm H2O
Which of the following is the most likely diagnosis?
- A) Herpes simplex virus (HSV)
- B) Rhinovirus
- C) Echovirus
- D) Flavivirus
- 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.24
This patient has viral (aseptic meningitis). Echovirus is the most common cause.
Photophobia and neck stiffness are highly characteristic of meningitis. Aseptic is more common
than bacterial.28
Bottom line: Echovirus is the most common cause of viral meningitis. At a bare minimum,
know the CSF findings for aseptic, bacterial, and fungal meningitis. RBCs in the CSF for HSV is
also HY.