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CT scan: an extra headache in meningitis or a necessary safety precaution?

Case presentation:

A 47-year-old woman with a past-medical history of fibromyalgia and lupus, presents to the emergency department with one month of progressive pain in her ankles, knees and lower back. She decided to come to the emergency department only when she developed acute onset of headache, neck stiffness, and chills that worsened over the past two days.

  • While her initial symptoms were consistent with prior rheumatologic flairs, the headaches were not. The patient is on several immunosuppressive therapies including mycophenolate and prednisone.

  • Vital signs: T 39.1 oC, BP 132/84, HR 105, RR 14, SpO2 100% on room air

  • Physical exam: No cranial nerve deficits, normal strength, tone, sensation, and reflexes. Mental status intact. Brudzinski negative; Kernig positive.

You are concerned about the possibility of bacterial meningitis in woman who is immunosuppressed. You want to perform a lumbar puncture and start antibiotic therapy.

Clinical question:

When is it necessary to perform a CT examination of the head prior to performing a lumbar puncture?

Summary of the evidence:

  • Acute bacterial meningitis has a case fatality rate between 10-30% even with appropriate treatment. [1]

  • Lumbar puncture is an essential component of the diagnostic pathway. While empiric therapy may be indicated, LP results guide definitive treatment. [2]

  • A review found that cerebral herniation occurs in about 5% of patients with acute bacterial meningitis and accounts for 30% of mortality [3]. The association of LP with herniation is debated in the literature [1,3,4], but because of the reported risk, IDSA guidelines recommend CT scan prior to LP if certain “red flags” are present during the initial evaluation. [2]

  • 2004 IDSA guidelines recommend two pathways in cases of presumed acute bacterial meningitis:

  • For patients with"red flags" (immunocompromise, history of CNS disease, new onset seizures, papilledema, altered consciousness, or a focal neurologic deficit), treatment should progress in this order:

  • Blood cultures

  • Dexamethasone and empiric therapy

  • CT scan

  • Lumbar puncture

  • If no red flags are present, treatment should progress in this order:

  • Blood cultures and lumbar puncture

  • Dexamethasone and empiric therapy

  • The IDSA guidelines and red flags are based in large part on a retrospective study of 301 patients with suspected meningitis. 96 out of the 301 did not have any of the IDSA red flags. In these 96 patients, a lack of red flags equated to a normal head CT 97% of the time (97% negative predictive value) [5]. Of the three patients who were misclassified, only one had a mild mass effect on CT and all three tolerated a lumbar puncture with no evidence of herniation a week after the procedure.

New evidence:

  • A recent retrospective study of a meningitis registry in Sweden, looked at 712 patients and compared the IDSA guidelines to a revised protocol that omitted altered consciousness as a “red flag” necessitating CT [4]. Adequate treatment was started 1.2 hours earlier and mortality and long-term sequala decreased under the revised protocol.

  • As an expansion of the first study, investigators used the same registry to directly compare IDSA guidelines to the new Swedish guidelines that only required CT if there are signs of cerebral herniation on physical exam, arm or leg drift, or prolonged/atypical symptoms [1].

  • In this study, US / IDSA guidelines led to CT scans of 65% of patients compared to only 7% in the new Swedish protocol. This difference in proportion was largely driven by the removal of an immunocompromised state and altered consciousness as red flags

  • Mortality and morbidity were reduced under the Swedish guidelines


  • There is debate in the literature about the association between lumbar puncture and herniation in patients with acute bacterial meningitis.

  • Practice guidelines may shift away from the more conservative IDSA guidelines to less stringent criteria that will lead to fewer patients receiving CT prior to lumbar puncture, especially in settings where there is limited access to CT scans. For now, US health care providers should continue to follow the 2004 IDSA guidelines which are standard of care.

  • The data are clear that acute bacterial meningitis is a medical emergency that confers significant morbidity and mortality. CT scan and lumbar puncture should not delay the initiation of appropriate therapy, particularly in "red flag" patients.


[1] Glimåker M, Sjölin J, Åkesson S, Naucler P. Lumbar Puncture Performed Promptly or After Neuroimaging in Acute Bacterial Meningitis in Adults: A Prospective National Cohort Study Evaluating Different Guidelines. Clin Infect Dis 2017;66:321–8. doi:10.1093/cid/cix806.

[2] Tunkel AR, Hartman BJ, Kaplan SL, Kaufman BA, Roos KL, Scheld WM, et al. Practice guidelines for the management of bacterial meningitis. Clin Infect Dis 2004;39:1267–84. doi:10.1086/425368.

[3] Joffe AR. Lumbar Puncture and Brain Herniation in Acute Bacterial Meningitis: A Review. J Intensive Care Med 2016;22:194–207. doi:10.1177/0885066607299516.

[4] Glimaker M, Johansson B, Grindborg O, Bottai M, Lindquist L, Sjolin J. Adult Bacterial Meningitis: Earlier Treatment and Improved Outcome Following Guideline Revision Promoting Prompt Lumbar Puncture. Clin Infect Dis 2015;60:1162–9. doi:10.1093/cid/civ011.

[5] 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;345:1727–33. doi:10.1056/NEJMoa010399.