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When Is CT Important Before Lumbar Puncture for Suspected Meningitis?

In patients with bacterial meningitis, deterioration can be rapid, and the sooner antibiotics are administered, the better the outcome (Ann Intern Med 1998; 129:862). However, empiric antibiotic therapy before culturing spinal fluid, blood, or both may prevent isolation and culture of the infecting organism. And because of concern that spinal tap might cause cerebral herniation, it is common practice first to obtain a CT scan of the head to exclude a mass lesion in patients with suspected meningitis. To review the risks associated with spinal tap and the benefits of obtaining an initial CT scan, these researchers prospectively reviewed the management of 301 patients older than 16 who were admitted to the emergency department with suspected meningitis.

CT was performed on 235 patients before spinal tap. Baseline clinical features associated with a high risk for abnormal findings on CT were age greater than 60, immunocompromise, history of a CNS lesion, a seizure within 1 week before presentation, an abnormal level of consciousness, and abnormal focal signs on examination (using the modified NIH stroke scale). Of 96 patients undergoing initial CT who had no risk factors for abnormal CT, only 3 had abnormal CT scans; none of the 3 had complications of the tap. Of 11 patients with mass effect on CT, 10 were identified based on the presence of 1 or more risk factors at baseline. Four patients had abnormal CT findings that precluded lumbar puncture; all 4 had at least 1 of the baseline risk factors. Lumbar puncture was performed an average of 2 hours later in the group that underwent initial CT than in the group that did not first undergo CT.

Comment: In adults with suspected bacterial meningitis without the described risk factors, performing immediate spinal tap and blood culture is likely the best management. In the presence of baseline risk factors, management should be: (1) blood culture (which may be positive even when spinal cultures are negative; see N Engl J Med 1993; 328:21), (2) intravenous antibiotics, and then (3) CT scan, followed by spinal tap unless the CT scan indicates increased risk for cerebral herniation.

— Michael Ronthal, MD, MBBCH, FRCP

Dr. Ronthal is Associate Professor of Neurology, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA.

Published in Journal Watch Neurology January 24, 2002

Citation(s):

Hasbun R et al. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med 2001 Dec 13; 345:1727-33.

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