CT (Almost) Never Before LP

The guidelines describing the patients with suspected bacterial meningitis for whom neuroimaging is indicated prior to lumbar puncture are quite broad. The Infectious Disease Society of America includes virtually every imaginable mental status or immune system impairment, and guidelines in Europe are similar. The anachronistic concern: cerebral herniation in the setting of increased intracranial pressure leading to an otherwise potentially avoidable death. But, guidelines in Sweden are different. In Sweden, their neuroimaging guidelines suggest only those virtually comatose or with focal neurologic signs should undergo CT prior to LP.

In this review of patients with acute bacterial meningitis from a Swedish registry, the authors attempt to parse out whether a decision to perform CT is not only unnecessary – but also potentially harmful. They analyze 815 patients ultimately diagnosed with bacterial meningitis and stratify them by those who received LP without CT, LP before CT, and CT before LP. Presenting features and comorbid medical conditions were abstracted retrospectively, and the results were analyzed with respect to the varying guideline recommendations, mortality, and functional outcomes.

The clear winner: CT rarely before LP, as in Sweden. By their guidelines, only ~7% of those ultimately diagnosed with bacterial meningitis had indication for CT prior to LP – but, unfortunately, 52% of patients underwent imaging anyway. The reason for “winning” if adherent to the Swedish strategy, however, was not just reduced resource utilization – it was mortality and functional outcomes. Mortality was almost halved in those for whom Swedish guidelines were followed, only rarely CT prior to LP. The authors attribute the signals for the underlying mortality difference to a greater percentage of patients receiving antibiotics within 1 hour or 2 hours when no CT was performed.

This probably overstates the magnitude of harm relating to CT use, as delays in antibiotics are probably more accurately delays in diagnosis, rather than logistics impacting timely delivery of antibiotics. After all, even in those with LP prior to CT, only 41% received steroids plus adequate antibiotics, so I expect the magnitude of effect seen here likely ties more reliably to confounding individual patient factors not easily adjusted for in a retrospective analysis.

That said, I do think the Swedes are doing the right thing – the vast majority of CTs were unhelpful. Their guidelines for neuroimaging – deep coma and/or lateralizing neurologic signs – will probably pick up any relevant findings (like the subdural empyema in this series), and reduce waste while obviating any possible delays in care.

“Lumbar puncture performed promptly or after neuroimaging in adult bacterial meningitis: A prospective national cohort study evaluating different guidelines”
https://academic.oup.com/cid/article-abstract/doi/10.1093/cid/cix806/4110207/Lumbar-puncture-performed-promptly-or-after

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