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Sorry, Can't Stop Doing Lumbar Puncture to Rule Out Subarachnoid Hemorrhage

A clinical decision rule performed well, but CT within 6 hours missed 20% of cases.

Depending on the number of slices, computed tomography (CT) of the brain misses up to 7% of subarachnoid hemorrhages (SAH). But a recent study suggested that if CT was performed within 6 hours of headache onset, the miss rate was zero (JW Emerg Med Aug 5 2011). Another study provided a decision rule that excluded all cases of SAH (JW Gen Med Nov 9 2010). Now, researchers retrospectively applied the decision rule and assessed the sensitivity of CT within 6 hours in adults with SAH who presented to 21 Kaiser Permanente emergency departments (EDs) in California from 2000 to 2011. All patients had normal neurological exams, initial negative CT results, and >5 red blood cells/µL of cerebrospinal fluid (CSF). SAH was diagnosed on the basis of presence of CSF xanthochromia or angiography findings of cerebral aneurysm or arteriovenous malformation.

The clinical decision rule would exclude SAH if none of the following are present: age 40, complaint of neck pain or stiffness, witnessed loss of consciousness, or onset of headache with exertion. Of 55 patients with SAH, 2.9% were missed by the clinical decision rule. Negative CT results were obtained within 6 hours of headache onset in 11 patients, for a CT miss rate of 20%; some of the false-negative CT results were obtained with modern, 64-slice scanners.

Comment: Sadly, this study shows that neither history and physical examination nor CT can rule out SAH. The authors suggest that combining this clinical decision rule and CT could allow us to forego lumbar puncture — if a miss rate of 1 in 500 is tolerable — but this requires further study. For now, we should continue to recommend lumbar puncture when ruling out SAH in a patient with a negative CT result.

— Daniel J. Pallin, MD, MPH

Published in Journal Watch Emergency Medicine February 15, 2013

Citation(s):

Mark DG et al. Nontraumatic subarachnoid hemorrhage in the setting of negative cranial computed tomography results: External validation of a clinical and imaging prediction rule. Ann Emerg Med 2012 Oct 1; [e-pub ahead of print]. (http://dx.doi.org/10.1016/j.annemergmed.2012.09.003)

Reader Remarks:

Review and add to remarks on this article

• Mistaken interpretation
  DH N, MSSM, 19 Feb 2013 1:05 PM EST
  Specialty: Emergency Medicine
  Reviewer error: This study neither finds nor concludes that all ED patients evaluated for SAH should undergo LP. Moreover, even... [more]
• Composite disease markers
  Adam Herbstritt, 19 Feb 2013 1:05 PM EST
  Specialty: Emergency Medicine
  'SAH was diagnosed on the basis of presence of CSF xanthochromia or angiography findings of cerebral aneurysm or arteriovenous malformation'... [more]
• This paper is not a game-changer!
  Stacy L Turner, Australia, 19 Feb 2013 1:05 PM EST
  Specialty: Emergency Medicine
  The paper is retrospective, and diagnosis of SAH was made with CSF >5 RBCs/uL and 1 of Cerebral aneurysm or... [more]
• SAH
  Zaw Aung, 19 Feb 2013 1:05 PM EST
  Specialty: Internal Medicine
  We also missed one patient who presents with neck pain, one episode of fainting attack, and headache. Neurological exam is... [more]
• subarachnoid bleeds
  ken mcfadden, 26 Feb 2013 1:11 PM EST
  Specialty: Emergency Medicine
  this is fishy. the 20% false negative rate flys in the face multiple prior studies. given the false positive rate... [more]
• Pretest probability
  me scott, 16 May 2013 3:07 PM EST
  Specialty: Emergency Medicine
  If I do a study on zebras, I will assume that all equines have stripes. If your starting point is... [more]

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