Head CT: When unnecessary before LP for meningitis

Caveat: This review only applies to those patients in whom you suspect meningitis. This does not apply to those being worked up for subarachnoid hemorrhage.

If ZERO of the following high risk features, it is safe to do LP without a Head CT.

High Risk Features Associated with an Abnormal CT

• Age ≥60 yr
• Immunocompromise (HIV, transplant, immunosuppression)
• History of CNS disease (mass lesion, CVA, focal infection)
• Seizure < 1 week prior to arrival
• Altered level of consciousness
• Unable to answer 2 questions correctly
• Unable to follow 2 commands correctly
• Gaze palsy
• Abnormal visual fields
• Facial palsy
• Arm or leg drift
• Abnormal language / speech

Study: Hasbun et al. NEMJ, 2001

Design: Prospective observational single-site study (n = 301)

Observed results:

• 235/301 underwent head CT
  • 56/235 (24%) had abnormal CT
    • 11/56 had mass effect

Validation arm: Applying the “high risk” criteria back to the enrollment group:

• 235/301 underwent head
  • 96/235 (41%) had no “high risk” features
    • 93/96 (97%) had a normal CT
      • 3/96 (3%) had 2 non-herniations and 1 mild herniation on CT
      • All 3 patients underwent LP without complications.

Results: Time savings for who did not undergo CT imaging (CT-)

• Time to antibiotics (3.8 hr for CT+ vs 2.9 hr for CT-)
• Time to LP (5.3 hr for CT+ vs 3.0 hr for CT-)

Limitations

• Study requires validation on a separate population, different from the derivation group

Conclusion

• If there are no abnormal “high risk” clinical features, you can safely perform a LP without a CT to assess for meningitis (NPV = 97%)
• Skipping the head CT prior to LP decreases time-to-antibiotics and time-to-LP

References

• Hasbun et al. CT of head before LP in adults with suspected meningitis. NEJM. 2001;345(24): 1727-33. [PubMed]