Is a CT Scan Necessary Prior to LP in Suspected Meningitis?
Abstract & Commentary
Synopsis: In this nicely performed prospective study, Hasbun and colleagues evaluated the usefulness of computed tomography (CT) in adults with suspected meningitis. They wanted to find out if the presence or absence of certain clinical features could predict that the CT scan would be normal. If the CT scan was likely to be normal, it could be avoided in the future during evaluation of adult patients with suspected meningitis, with potentially significant cost savings.
Source: Hasbun R, et al. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med. 2001;345:1727-1733.
Hasbun and colleagues evaluated all patients older than 16 years of age who presented to the Yale-New Haven hospital emergency department with clinically suspected meningitis irrespective of whether a CT scan was performed. They excluded patients who had a CT scan done before a full examination as described in the study protocol. They also excluded patients if they did not undergo a lumbar puncture subsequent to CT scan, as they could not decide in those patients if there would have been any complications of lumbar puncture or whether the patient had meningitis. Out of 511 patients who were screened, 301 patients entered the study. Hasbun et al collected extensive routine data, including clinical features, immune status, comorbidity index, laboratory results, and management decisions. They also tried to follow a large number of clinical and laboratory features for 1 week after the entry into study, an effort that was successful in almost all the patients. They used the Modified NIH stroke scale to evaluate patients’ neurological status. Two neuroradiologists evaluated the CT scans and were in agreement in all but 3 cases. The CT scans were categorized as normal, showing focal abnormality (with or without mass effects), or demonstrating a nonfocal abnormality, with or without mass effects.
Out of 301 patients in the study, 27% had pre-existing conditions; the majority of these (25%) were due to HIV infection. Eight percent of the patients had a history of central nervous system disease. Headache was the most common symptom (79%), followed by fever (67%); photophobia was seen in 50%. Most patients (91%) had normal mental status (GCS 14 or 15), and about 17% had abnormal findings based upon the NIH stroke scale. A total of 235 patients (78%) underwent CT scan of head before undergoing lumbar puncture. Resident doctors and attending physicians requested CT scan in equal proportions of the patients seen by them. Among 201 physicians who were surveyed in the hospital, more than half said they ordered CT scan because they suspected focal brain findings; a third thought it was "standard of care," and 5% indicated that they ordered scans to avoid litigation. Five percent of the physicians had more than one of the above reasons. A total of 76% (179 patients) of the CT scans were normal. Twenty-four percent (56 patients) had abnormal scans. Only 11 patients out of these 56 had mass effect on CT scan. Nine patients had focal abnormality and a mass effect, whereas only 2 patients had nonfocal abnormality and a mass effect.
After analysis, Hasbun et al came up with a group of findings that were associated with an abnormal CT scan finding. These included age > 60, immunocompromised state, history of CNS disease, history of seizure within one week of presentation, and abnormal findings on neurological examination. The abnormal findings on neurological examination included abnormal level of consciousness, inability to answer 2 questions correctly, inability to follow 2 commands correctly, gaze palsy, abnormal visual field, arm, or leg drift, or abnormal language. A total of 235 patients underwent lumbar puncture after undergoing CT scan. Among them, 96 patients had none of these characteristics at baseline. In 93 of these 96 patients, the CT scan was normal and the CT scan showed mass effect in only 1 patient. Among all 235 patients who underwent CT scan, only 4 had an abnormal CT scan that resulted in a change in the clinical decision to avoid lumbar puncture. All 4 of these patients had one or more characteristics that would have predicted an abnormal CT scan.
Of 289 patients in whom data were available 1 week after lumbar puncture, none had developed herniation. Thus, Hasbun et al concluded that in adults with suspected meningitis, clinical features can be used to identify patients who have a normal CT scan and, thus, can have this examination deferred.
Comment by Uday B. Nanavaty, MD
Why did I call this a nicely done study in spite of the fact that only 5 of these 301 patients ended up with confirmed diagnosis of bacterial meningitis? I liked the study for several reasons. Most importantly, the study showed that even as we enter 2002, simple things included in the history and physical examination can be used to make valuable decisions, and that history and physical examination done correctly can be not only money saving but also time saving. As noted by Hasbun et al, patients waited on an average 2 more hours when CT scan was performed before lumbar puncture, which on an average was delayed up to 3 hours after arrival.
Another feature I like about the study is that Hasbun et al took a comprehensive approach to the evaluation of the presenting clinical problem. They included facts such as that it took on an average about 10 minutes to complete the rather detailed neurological examination that was part of the protocol. That would be a short time considering the time spent obtaining a CT scan prior to performing a lumbar puncture.
Hasbun et al did not highlight the reasons, symptoms and signs used to suspect acute meningitis. A previous systemic review (Attia J, et al. JAMA. 1999;282:175-181) of diagnosis of acute meningitis in adults had suggested that complete absence of the classic triad of fever, neck stiffness. and an altered mental status virtually eliminates the possibility of meningitis. That particular review had further suggested that abnormal mental status is a very sensitive symptom to suggest meningitis, and that a completely normal mental status in a low-risk patient would be another reason not to suspect meningitis.
Dr. Nanavaty is Senior Research Fellow, Department of Critical Care Medicine, National Institutes of Health.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content