Test Your Knowledge : Ten Questions about Abnormal Cerebrospinal Fluid Results

Question 10. The CSF in West Nile encephalitis typically shows which of the following? A moderate lymphocytic pleocytosis, moderately increased protein, and a normal CSF: plasma glucose ratio A normal cell count, highly elevated protein, and a reduced CSF: plasma glucose ratio No abnormalities Test Your Knowledge: Ten Questions about Abnormal Cerebrospinal Fluid Results This quiz is related to the Learning Forum article in the October issue of PLoS Medicine (DOI: 10.1371/ journal.pmed.0010007).


Question 3. Which of the following is true about the CSF changes in patients with tuberculous meningitis?
The cell count is often elevated, and the cells are mainly neutrophils In detecting M. tuberculosis in the CSF by nucleic acid amplifi cation tests (such as polymerase chain reaction [PCR]), the sensitivity and specifi city are close to 100% A normal CSF does not exclude cerebral tuberculosis Question 4. Which of the following does not cause the CSF picture of "aseptic" meningitis?

Test Your Knowledge: Ten Questions about Abnormal Cerebrospinal Fluid Results
This quiz is related to the Learning Forum article in the October issue of PLoS Medicine (DOI: 10.1371/ journal.pmed.0010007).Answer 1.A glucose level that is less than 50% of the plasma glucose level Normal CSF fi ndings are a glucose level greater than 50% of the plasma glucose level, a protein level of less than 0.5 g/l, and 0-5 cells/µl (usually monocytes).

Answer 2. Moderately elevated CSF lymphocyte count of 200 cells/µl, raised protein, and low glucose
In fungal meningitis, the CSF most commonly shows a moderately elevated lymphocyte count [1].Classically, the glucose is low and protein elevated.Not all patients with fungal meningitis have marked CSF changes-for example, the cellular changes may be minimal in patients with advanced AIDS and cryptococcal meningitis.

Answer 3. A normal CSF does not exclude cerebral tuberculosis
Classical CSF changes in tuberculous meningitis are the following: markedly elevated CSF protein, raised lymphocyte count, and a low glucose.A small proportion of cases may present with neutrophils in the CSF or a mixed picture with both neutrophils and lymphocytes.A systematic review and meta-analysis of nucleic acid amplifi cation tests for tuberculous meningitis found that these tests have a sensitivity of 56% (95% CI 46%-66%) and a specifi city of 98% (95% CI 97%-99%) [1].The CSF may be normal or have only minor changes in cerebral abscesses due to tuberculosis (tuberculomas).

Answer 4. Bacterial meningitis
Aseptic meningitis is usually taken to mean a CSF picture dominated by lymphocytes or mononuclear cells with no organisms seen on microscopy [1,2].Viral meningitis is the most common cause.Tuberculosis must be considered in all cases, as well as other atypical infections such as Lyme disease or brucellosis.Non-infectious causes include drug-induced meningitis, Vogt-Koyanagi-Harada syndrome, connective tissue diseases, and sarcoidosis.

Answer 5. Common bacterial pathogens may be identifi ed by rapid polysaccharide antigen detection
The causative organism in bacterial meningitis may be rapidly diagnosed by CSF detection of bacterial antigens for Haemophilus infl uenzae, pneumococcus, and meningococcus [1].This can be particularly useful if recent antibiotic therapy has led to the CSF culture being negative.PCR detection of bacterial DNA is more sensitive, and PCR is becoming more widespread, but in most laboratories it cannot be deployed in "real time."CSF lactate is raised in bacterial meningitis, and this fact has been used to aid diagnosis in some settings [2].Early antibiotic administration is essential in bacterial meningitis and should not be deferred if there is to be a signifi cant delay in performing a lumbar puncture [3].

Answer 6. Sarcoidosis
Neurosarcoid produces an abnormal CSF in at least 80% of cases.Typical changes include a raised protein and an increased density of cells, which are predominantly monocytes.Low CSF glucose may occur with neurosarcoid, making distinction from tuberculosis diffi cult [1].

Answer 9. Enteroviruses
In the UK, enteroviruses are the most common cause of viral meningitis in immunocompetent adults.CSF changes in viral meningitis are relatively nonspecifi c, with an elevated lymphocyte count and protein level and a normal CSF glucose.PCR is now the diagnostic modality of choice for central nervous system viral infections but is not available in "real time" within most centers.Answer 10.A moderate lymphocytic pleocytosis, moderately increased protein, and a normal CSF: plasma glucose ratio Examination of the CSF in West Nile encephalitis typically shows a moderate lymphocytic pleocytosis, though sometimes there may be no cells, or neutrophils may predominate.Protein concentrations are moderately increased, and the glucose ratio is typically normal [1].
Citation: Yamey G, Lynn W, Lightman S (2004) Test your knowledge: Ten questions about abnormal cerebrospinal fl uid results.PLoS Med 1(1): e011.Copyright: © 2004 Yamey et al.This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Gavin Yamey is the Magazine Editor of PLoS Medicine.William Lynn and Susan Lightman are the Section Editors of the Learning Forum and are on the PLoS Medicine editorial board.*To whom correspondence should be addressed.E-mail: gyamey@plos.orgDOI: 10.1371/journal.pmed.0010011