EBQ:Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage

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Complete Journal Club Article
Perry, J et al.. "Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study". BMJ. 2015. 18(350):epub.
PubMed Full text PDF

Clinical Question

  • Can cerebrospinal fluid from patients with acute headache after traumatic lumbar puncture be distinguished from subarachnoid hemorrhage?

Conclusion

  • No xanthochromia and red blood cell count < 2000 × 106/L can reasonably excludes the diagnosis of aneurysmal subarachnoid hemorrhage.

Major Points

  • In ruling out traumatic subarachnoid hemorrhage, the traumatic tap which causes blood to mix with cerebrospinal fluid can complicate the diagnosis of subarachnoid hemorrhage in up to 30% of LPs.[1]

This study was a predefined subsidy of the Canadian subarachnoid hemorrhage (SAH) rule and provides data to classify the likelihood of a subarachnoid hemorrhage based on LP results. Using a threshold of 2000x106/L in the final CSF tube provides for a sensitivity of 100% (CI 74.7-100%) and specificity of 91.2% (88.6-93.3%). For xanthochromia however the sensitivity was only 46.6% (CI 22-72.6%) for diagnosing subarachnoid. Combining the RBC threshold with xanthochromia the sensitivity for subarachnoid hemorrhage is 100%[2]


Study Design

  • Planned substudy from the prospective multi center cohort study, designed to derive and validate the Ottawa SAH (subarachnoid hemorrhage) rule
  • Conducted between November 2000 - December 2009
  • Multicenter at 12 canadian academic EDs

Population

N=1739

Patient Demographics

  • Mean Age: 43yo
  • Sex: 40% Men/60% Women

Inclusion Criteria

  • Age >15
  • Alert patients (GCS =15)
  • ED patents with acute non-traumatic headache undergoing LP to rule out subarachnoid hemorrhage
  • Within 14 days of headache onset

Exclusion Criteria

  • Recurrent headaches (3 or more with similar character/intensity over 6 month or greater period
  • Transfered from other hospital with confirmed subarachnoid
  • Presence of focal neurologic deficits or papilledema
  • History of
    • Subarachnoid hemorrhage
    • Aneurysm
    • VP shunt
    • Brain neoplasm

Interventions

  • Computed tomography and/or lumbar puncture was performed at the discretion of the treating physician
    • Some LPs were performed before CT scans
  • Patients discharged without having both computed tomography imaging and a normal result on lumbar puncture were assessed by telephone interview one month and six months after assessment in the emergency department as well as a review of medical records to identify any recorded subarachnoid hemorrhage.
  • Patients without telephone follow-up or subsequent hospital encounters at the enrolling sites were further checked against the coroner’s records to identify any deaths compatible with subarachnoid hemorrhage

Outcomes

Subarachnoid hemorrhage definition:

  • Blood in the subarachnoid space on CT brain
  • Xanthochromia on examination of CSF
  • Red blood cells in the final tube of CSF fluid and aneurysm shown with cerebral angiography requiring any neurovascular intervention or resulting in death.

Normal LP = 1098 Abnormal LP = 641 (36.9%)

  • No aneurysmal subarachnoid = 626
  • Aneurysmal subarachnoid 15
  • Xanthochromia = 7
  • No Xanthochromia = 8

Primary Outcome

There were 15 (0.9%) patients with aneurysmal subarachnoid hemorrhage based on abnormal results of a lumbar puncture.

Secondary Outcomes

The presence of less than 2000 × 106/L red blood cells in addition to no xanthochromia excluded the diagnosis of aneurysmal subarachnoid hemorrhage

  • Sensitivity of 100% (95% confidence interval 74.7% to 100%)
  • Specificity of 91.2% (88.6% to 93.3%).


Subgroup analysis

Characteristics or patients in Canadian SAH Rule Study

All patients in the SAH Rule derivation and validation cohort[3]

  • Neck Pain or stiffness: 33.7%
  • Median time of headache onset to peak: 60 seconds
  • CT performed: 81.7%
  • Mean time from headache onset to LP: 18 hours
  • Median RBC count in last tube: 0
  • Aneurysmal subarachnoid hemorrhage: 3.5%

Characteristics of patients with abnormal LP

Positive xanthochromia

  • Aneurysmal subarachnoid hemorrhage: 46.6%
  • No Subarachnoid: 2.6%

Median RBC count in last tube (x106)

    • Aneurysmal subarachnoid: 28741
    • No subarachnoid: 20

Angiography rate

  • Aneurysmal subarachnoid hemorrhage: 15%
  • No subarachnoid: 64.5%

Criticisms & Further Discussion

  • Although this study is useful for defining the number of RBCs concerning for a SAH it does not help guide the workup for patients with a negative CT and positive lumbar puncture. There was also a great percentage of patients who underwent CT angiography for a small percentage of SAH.
  • A study by Gorchynski found that RBC counts ≤ 500 x106/L in the 4th CSF tube had a 100% negative predictive value for subarachnoid hemorrhage[4]
  • Caution should be used for assessing abscess of SAH based on the percentage drop in RBC count since the presence of SAH was demonstrated in patients with a 25% reduction of RBCs between the 1st and 4th tubes[5]

External Links

Funding

Funded by the Canadian Institutes of Health Research (grants: 67107, 153742), the Ontario Ministry of Health and Long Term Care, and the physicians of Ontario through the Physician’s Services Incorporated Foundation

References

  1. ↑ Gorchynski J, Oman J, Newton T. Interpretation of traumatic lumbar punctures in the setting of possible subarachnoid hemorrhage: who can be safely discharged? Cal J Emerg Med 2007;8:3–7.
  2. ↑ Perry JJ et al. Should spectrophotometry be used to identify xanthochromia in the cerebrospinal fluid of alert patients suspected of having subarachnoid hemorrhage? Stroke 2006;37:2467–72.
  3. ↑ Perry JJ. et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013 Sep 25;310(12):1248-55.
  4. ↑ Gorchynski J. et al. Interpretation of traumatic lumbar punctures in the setting of possible subarachnoid hemorrhage: who can be safely discharged? Cal J Emerg Med 2007;8:3–7.
  5. ↑ Heasley DC et al. Clearing of red blood cells in lumbar puncture does not rule out ruptured aneurysm in patients with suspected subarachnoid hemorrhage but negative head CT findings. Am J Neuroradiol 2005;26:820–4.
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