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    Lumbar puncture on a patient with suspected meningitis

    By   ·  1 minute read

    You perform lumbar puncture on a patient with suspected meningitis. Red blood cells (RBCs) are found in the cerebrospinal fluid (CSF). You compare the RBC counts in the first and last tubes to help differentiate the cause of the RBCs. 

    image (24)

    If the first and last tubes have the same number of RBCs, and, after being centrifuged, the samples have the appearance of the tube on the right in the picture above, the most likely diagnosis is which of the following?

    • subarachnoid hemorrhage
    • traumatic tap
    • fungal meningitis
    • subdural hematoma
    • epidural hematoma
    The correct answer is:

    subarachnoid hemorrhage

     

    Normal CSF has no RBCs. RBCs found in CSF suggest either a traumatic tap or a subarachnoid hemorrhage. If the first tube of CSF has many RBCs but they clear by the last tube, traumatic tap is suggested.

    A sample revealing xanthochromia, which is yellow hue resulting from the degradation of hemoglobin, is suggestive of subarachnoid hemorrhage (see above image).

    By contrast, someone with bacterial meningitis would be expected to have no or nearly no RBCs (or, if RBCs are present, they would clear by the final sample tube), decreased glucose, elevated protein, more than 1000 leukocytes/mm3 with 85%-90% neutrophils, and a positive Gram stain and culture.

    References:

    Garcia CG, McCracken GH Jr. Acute bacterial meningitis beyond the neonatal period. In: Long SS, et al. Principles and Practice of Pediatric Infectious Disease. 4th ed., 2012:272-278.

    Lehman R, Schor N. Neurologic evaluation. In: Kliegman RM, et al. Nelson Textbook of Pediatrics. 19th ed., 2011.

     

    This question appears in Med-Challenger Pediatric Medicine Exam Review with CME

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