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Analysis of Cerebrospinal Fluid

Прочитайте:
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CSF analysis is essential. Typical patterns of findings in the CSF pressure and CSF analysis follow in the Table 1 regarding bacterial versus viral versus fungal (including cryptococcal) meningitis or encephalitis.

Table. Cerebrospinal Fluid Findings by Type of Organism (Open Table in a new window)

CSF Finding (Normal) Bacterial Meningitis Viral Meningitis* Fungal Meningitis
Pressure (5-15 cm water)
  • Increased
  • Normal or mildly increased
  • Normal or mildly increased in most fungal and tuberculous CNS infections
  • Patients with AIDS and cryptococcal meningitis are at increased risk of blindness and death unless pressure maintained at < 30 cm
Cell counts, mononuclear cells/µL Preterm (0-25) Term (0-22) 6 mo+ (0-5)
  • Normal cell count excludes bacterial meningitis
  • Typically thousands of polymorphonuclear cells, but counts may not change dramatically or even be normal (classically in very early meningococcal meningitis or in extremely ill neonates)
  • Lymphocytosis with normal CSF chemistry results observed in 15-25% of patients, especially if counts < 1000 or if patient is partially treated
  • About 90% of patients with ventriculoperitoneal shunts and CSF WBC count >100 cells/µL are infected, though CSF glucose level often normal, and bacteria often less pathogenic
  • Cell count and chemistry levels normalize slowly (days) with antibiotics
  • Usually < 500, nearly 100% mononuclear
  • < 48 hours, clinically significant polymorphonuclear pleocytosis may be indistinguishable from early bacterial meningitis, particularly with EEE
  • Nontraumatic RBCs in 80% of patients with HSV meningoencephalitis, though 10% have normal CSF results
  • 100s of mononuclear cells
Microorganisms (none)
  • Gram stain 80% effective
  • Inadequate decolorization may cause Haemophilus influenzae to be mistaken for gram-positive cocci
  • Pretreatment with antibiotics may affect stain uptake, causing gram-positive species to appear to be gram-negative and decrease culture yield by an average of 20
  • No organism
  • India ink 80-90% effective for detecting fungi
  • AFB stain 40% effective for TB; increase yield by staining supernatant from at least 5 mL of CSF
Glucose† Euglycemia (>50% serum) Hyperglycemia (>30% serum)
  • Decreased
  • Normal
  • Sometimes decreased
  • In addition to fulminant bacterial meningitis, TB, primary amebic meningoencephalitis, and neurocysticercosis cause low glucose levels
Protein Preterm (65-150 mg/dL) Term (20-170 mg/dL 6 mo+ (15-45 mg/dL)
  • Usually >150 mg/dL
  • May be >1000 mg/dL
  • Mildly increased
  • Increased >1000 mg/dL, with relatively benign clinical presentation suggestive of fungal disease
*Some bacteria (eg, Mycoplasma, Listeria, Leptospira, Borrelia burgdorferi [Lyme disease]) cause alterations in spinal fluid that resemble the viral profile. An aseptic profile is also typical of partially treated bacterial infections (>33%, especially those in children, are treated with antimicrobials) and of the 2 most common causes of encephalitis—the arboviruses and the potentially curable HSV. † Wait 4 hours after glucose load. AFB—acid-fast bacillus; CSF—cerebrospinal fluid; EEE-eastern equine encephalitis; HSV—herpes simplex virus; RBC—red blood cell; TB—tuberculosis; WBC—white blood cell.

The most important diagnostic test in the emergency department (ED) to rule out bacterial meningitis is prompt Gram staining and, if available, polymerase chain reaction (PCR) of the CSF in patients with suspected HSV encephalitis. PCR for HSV DNA is 100% specific and 75-98% sensitive within the first 25-45 hours. Types 1 and 2 cross-react, but no cross-reactivity with other herpes viruses occurs. Arguably, a series of quantitative PCRs documenting the decline of viral load with acyclovir treatment is strongly supportive of the diagnosis of HSV, and selected patients my avoid need for brain biopsy.

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