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    Meningitis – Diagnosis

    Infections, Neurological

    Last Updated Aug 26, 2019
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    • Meningitis is caused by bacterial, viral, or fungal pathogens.
    • Annual incidence of invasive meningococcal disease is approximately 0.3-3 per 100,000 population worldwide, and 0.58 per 100,000 population in Canada.
    • Bacterial meningitis has a mortality rate of 15% even with early diagnosis and treatment.
    • Typical bacterial pathogens in include:
      • Streptococcus pneumonia (60%)
      • Neisseria meningitides (15%)
      • Haemophilus influenza (7%), and
      • Listeria monocytogenes (3%) (Neonates (usually < 29 days old), age > 50 yrs, immunocompromised, pregnant)
      • Group B Streptococcus in neonates.
    • Chronic meningitis is often caused by fungal infection and is associated with an immunocompromised host (HIV/AIDS, chronic steroid therapy, cancer patients):
      • Cryptococcus neoformans
      • Coccidioides immitis
      • Aspergillus
      • Candida
      • Mucormycosis (diabetics; direct extension of sinus infection).
    • Viral encephalitis may also present with meningismus and/or delirium.
    • Rash or petechiae suggest meningitidis,but can occur in overwhelming S. pneumococcal infection (especially in asplenic patients).

    Diagnostic Process

    • In adults with community-acquired acute bacterial meningitis, the sensitivity of the classic triad of fever, neck stiffness, and altered mental status is low (44%), but almost all (95%) present with at least two of the four symptoms of headache, fever, neck stiffness, and altered mental status (van de Beek et al., 2004; n= 696 patients).
    • Absence of all of these symptoms essentially rules out the diagnosis.
    • Other tests for meningeal irritation have low value:
      • Kernig sign (5% sensitivity, 95% specificity)
        • unable to fully extend knee with the hip flexed at 90 degrees
      • Brudzinski sign (5% sensitivity, 95% specificity)
        • spontaneously flexes the hips and knees during passive neck flexion
      • Jolt accentuation (97% sensitivity, 60% specificity)
        • headache accentuated by rapid horizontal rotation of the head.
    • Routine blood work can be normal even in the presence of severe CNS infection.
    • Blood cultures should be obtained before antimicrobials (as 50 – 90% are positive).
    • Definitive diagnosis cerebrospinal fluid (CSF) analysis, culture, and PCR.
    • Empirical treatment should be considered if LP delayed > 30 minutes.


    Indications for head CT scan before LP

    • Controversial whether performing the LP or the increased intracranial pressure is the inciting event causing brain herniation/death in the setting of acute bacterial meningitis.
      • 5% of patients with bacterial meningitis will herniate even without an LP.
      • A normal head CT does not preclude increased intracranial pressure or impending brain herniation.
    • Current guidelines recommend empiric antibiotics, supportive care, and obtaining neurological opinion while forgoing the LP if there is clinical suspicion of increased intracranial pressure or impending brain herniation:
      • Altered mental status or GCS.
      • Immunocompromised (i.e. HIV infection, immunosuppressive therapy, solid organ or hematopoietic stem cell transplant, asplenic).
      • Known CNS disease (i.e. mass lesion, stroke, focal infection).
      • New-onset seizure.
      • Papilledema focal neurological deficit.

    LP without a head CT scan is considered safe if none of the above are present

    • Prospective study of 301 adults with suspected meningitis: 78% underwent head CT before LP and 24% had abnormal CT findings but only 5% had a mass effect (Hasbun, et al., 2001).

    If LP cannot be performed in suspected meningitis, do not delay antimicrobial therapy

    • If LP is delayed > 30 minutes: obtain blood cultures, administer steroids before or at the same time as initiation of empiric antimicrobial therapy.
    • A pathogen can still be cultured from the CSF in most patients up to several hours after the administration of antimicrobial agents, with the exception of meningococcus. Polymerase chain reaction (PCR) is useful in these cases.

    Relative Contraindications for LP

    • Increased ICP (ie. mass effect on CNS imaging or clinical signs of impending herniation).
    • Platelets < 50,000 plts/μL.
    • INR > 1.4 or on anticoagulation.
    • Suspected spinal epidural abscess.
    • Infection at the puncture site.

    Management of the Patient at high risk for bleeding

    • Best to give antibiotics and rely on blood culture results (consider PCR on delayed LP).
    • If LP is still considered urgent and consider consultation with a haematologist and neurologist.
    • Do not perform an LP in patients with coagulation defects who are actively bleeding, have severe thrombocytopenia (ie. platelet counts <50,000/μL), or an INR >1.4
    • For elective procedures in a patient receiving systemic anticoagulation, stop the following agents for the specified period of time prior to LP:
      • Unfractionated IV heparin drips – 2 to 4 hours.
      • Low-molecular-weight heparin – 12 to 24 hours.
      • Warfarin – 5 to 7 days. Or give FFP or Octaplex.
      • Direct oral anticoagulants (DOACs) apixaban, edoxaban, and rivaroxaban – 48 hours. Dabigatran should be held for 48 to 96 hours based on renal function.
      • Subcutaneous heparin: <10,000 units per day is not believed to pose a substantial risk for bleeding.

    How to perform an LP

    • Patient in the lateral recumbent or prone positions (preferred), or sitting upright.
    • 20-or 22-gauge spinal needles are generally recommended.
    • Smaller needle size (higher gauge) and atraumatic needle tip (as opposed to the conventional cutting tip) lower the incidence of post-dural puncture headache (PDPH).
    • PDPH occurs in as much as 50% of patients when a 20 gauge needle is used, and in 20 to 30% of patients when a 22 gauge needle is used.
    • Typical opening pressure is < 20 cm H20.
    • A total of 8 to 15 mL of CSF is typically removed, however, up to 40 mL of fluid can be removed if special tests (ie. cytology, mycology, virology) are indicated.
    • Collect 1.5 to 2 cc’s of fluid in each of 4 or 5 test tubes.
    • Send for the following laboratory tests for each tube:
      • Tube 1 – cell count
      • Tube 2 – stat gram stain and culture
      • Tube 3 – glucose and protein
      • Tube 4 – cell count (comparison to Tube 1)
      • Tube 5 (optional) – special tests such (ie. virology, mycology, cytology).

    Related Information

    Reference List

    1. UpToDate: Lumbar puncture: Technique, indications, contraindications, and complications in adults

    2. UpToDate: Post dural puncture headache

    3. UpToDate: Clinical features and diagnosis of acute bacterial meningitis in adults

    4. Rosen’s Emergency Medicine: Central Nervous System Infections, Chapter 99, 1328-1340. e9

    5. Oordt-Speets AM, Bolijn R, van Hoorn RC, Bhavsar A, Kyaw MH. Global etiology of bacterial meningitis: A systematic review and meta-analysis. PLoS One. 2018 Jun 11;13(6):e0198772. doi: 10.1371/journal.pone.0198772. eCollection 2018.

    6. Invasive Meningococcal Disease. Government of Canada Public Health Services.

    7. Meningococcal Disease in Other Countries. Centers for Disease Control and Prevention

    8. Lumbar Puncture Quick Guide. Faculty of Medicine, University of Ottawa, 
      Version January 2, 2003.

    9. Brink M, Welinder-Olsson C, Hagberg L. Time window for positive cerebrospinal fluid broad-range bacterial PCR and Streptococcus pneumoniae immunochromatographic test in acute bacterial meningitis. Infect Dis (Lond). 2015;47(12):869-77. doi: 10.3109/23744235.2015.1078907.

    10. Rochwerg B, Almenawer SA, Siemieniuk RAC, Vandvik PO Agoritsas T, Lytvyn L, Alhazzani W, Archambault P, D’Aragon F, Farhoumand PD, Guyatt G, Laake JH, Beltrán-Arroyave C, McCredie V, Price A, Chabot C, Zervakis T, Badhiwala J, St-Onge M, Szczeklik W, Møller MH, Lamontagne F. Atraumatic (pencil-point) versus conventional needles for lumbar puncture: a clinical practice guideline. BMJ. 2018 May 22;361:k1920. doi: 10.1136/bmj.k1920.

    11. van de Beek D1, de Gans J, Spanjaard L, Weisfelt M, Reitsma JB, Vermeulen M. Clinical features and prognostic factors in adults with bacterial meningitis. N Engl J Med. 2004 Oct 28;351(18):1849-59.

    12. Hasbun R, Abrahams J, Jekel J, Quagliarello VJ. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med. 2001 Dec 13;345(24):1727-33.

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