Is CT Necessary Before LP in Suspected Meningitis?
Is CT Necessary Before LP in Suspected Meningitis?
Abstract & Commentary
Synopsis: This prospective emergency department study identified clinical criteria that have a 97% predictive value for a normal head CT in patients that could safely undergo LP without a CT scan.
Source: Hasbun R, et al. N Engl J Med. 2001;345:1727-1733.
In this study, Hasbun and colleagues prospectively selected 11 elements of the Modified National Institutes of Health (NIH) Stroke Scale and tested how well they predict which suspected meningitis patients will have normal computed tomography (CT) of the head. The criteria tested were absence of: age older than 60, history of immunocompromise, history of central nervous system disease, seizure within 1 week, an abnormal level of consciousness, inability to answer 2 consecutive questions correctly, gaze palsy, abnormal visual fields, facial palsy, arm drift, leg drift, and abnormal language. At the Yale New Haven Emergency Department, 301 patients were enrolled sequentially from 1995-1999. Two hundred thirty-five (78%) underwent CT before lumbar puncture (LP). Of these, 189 (76%) had normal head CT. Ninety-six (40%) of these patients had none of the abnormal clinical findings listed, and of these 93 (97%) had normal head CT. The 3 patients with normal clinical findings but abnormal CT underwent LP without brainstem herniation. Among the 56 (24%) patients with abnormal clinical findings and abnormal CT, 4 had findings that caused clinicians to avoid LP and 2 of these patients eventually died with brain herniation without LP. Had these 11 clinical findings been used as criteria to not order CT prior to LP, 40% fewer scans would have been ordered without apparent harm. Hasbun et al also found that patients that had LP without first having CT had: 1) a shorter time from admission to LP, 3.0 hours vs. 5.3 hours (P < 0.001); and 2) a trend toward shorter time to antibiotic therapy, 2.9 hours vs. 3.8 hours (P = 0.09).
Comment by Mark Potter, MD
Bacterial meningitis is a medical emergency that requires collection of cerebrospinal fluid for optimal diagnosis and treatment. Since the 1950s, however, fatal brain stem herniation has been recognized as a rare complication of LP. Elevated intracranial pressure, especially in the setting of unilateral brain lesions, inflammatory lesions (eg, toxoplasmosis, subdural empyema, brain abscess), intracranial hemorrhage, cerebral edema, sagittal sinus thrombosis, or central vein thrombosis increases the risk of herniation. CT scanning can identify many of these risk factors and is commonly ordered prior to LP. In this study, 44% of physicians surveyed cited the standard of care or fear of litigation as their reason for ordering the CT prior to LP. Concerns persist, however, about negative effects of routine CT scanning before LP. Concerns about delays in antibiotic treatment have been somewhat mitigated by the widely accepted practice of starting empiric antibiotic therapy prior to LP if LP is to be delayed for any reason. The exact effect of antibiotics before LP on the diagnostic use of cerebrospinal fluid cultures continues to be debated. The extra costs of scanning and prolonged ED time are also concerns. No broad consensus guideline currently exists to aid clinicians in determining when CT is needed prior to LP. This article provides some support to those seeking a clinical basis for more selective use of CT scanning in cases of suspected meningitis, but further validation in other settings and with larger cohorts will be needed to establish a clear evidence-based standard in this area.
Dr. Potter is Assistant Professor of Family Medicine, Loyola University Medical School, Chicago, Ill.
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