What scores can be used to rule out abnormalities in headache patients, such as subarachnoid hemorrhage?

Clinical Scores for Ruling Out Abnormalities in Headache Patients

The Ottawa Subarachnoid Hemorrhage (SAH) Rule is the most validated and effective clinical decision tool for ruling out subarachnoid hemorrhage in patients with acute headache, demonstrating 100% sensitivity in multiple validation studies. 1

Ottawa SAH Rule

The Ottawa SAH Rule is designed for alert patients over 15 years of age with new severe non-traumatic headache reaching maximum intensity within 1 hour. According to this rule, patients require further investigation for SAH if they have any of the following criteria:

1. Age ≥40 years
2. Neck pain or stiffness
3. Witnessed loss of consciousness
4. Onset during exertion
5. Thunderclap headache (instantly peaking pain)
6. Limited neck flexion on examination

Evidence Supporting the Ottawa SAH Rule

The Ottawa SAH Rule has been extensively validated in multiple studies:

• Initial validation by Perry et al. showed 100% sensitivity with 15.3% specificity 2
• External validation in a multicenter study demonstrated 100% sensitivity (95% CI 94.6%-100%) with specificity of 13.6% 3
• Additional external validation studies confirmed 100% sensitivity with varying specificity (7.6% in one study, 44.2% in another) 4, 5

Clinical Application Algorithm

For patients presenting with headache:

1. Initial Assessment: Determine if the headache reached maximum intensity within 1 hour

   • If no → Ottawa SAH Rule does not apply
   • If yes → Proceed to step 2

2. Apply Ottawa SAH Rule: Check for any of the six criteria

   • If none present → SAH can be safely ruled out (100% negative predictive value) 3
   • If any present → Proceed to diagnostic testing

3. Diagnostic Testing:

   • For patients presenting within 6 hours of headache onset without neurological deficits:

     • Non-contrast head CT on high-quality scanner interpreted by a board-certified neuroradiologist is sufficient to rule out SAH (sensitivity 98.7%, specificity 99.9%) 1

   • For patients presenting >6 hours from onset or with neurological deficits:

     • Non-contrast head CT followed by lumbar puncture if CT is negative 1

Important Clinical Considerations

• High-Risk Features: Clinical characteristics in history that distinguish SAH headache include occipital location, stabbing quality, presence of meningism, and onset during exertion 6

• Limitations of the Ottawa SAH Rule:

  • Low specificity (7.6-44.2% across studies) means many patients without SAH will still require further testing 4, 5
  • Only applicable to a subset of headache patients (approximately 9% of all ED headache presentations in one study) 5

• Pitfalls to Avoid:

  • Misdiagnosis of SAH occurs in up to 12% of cases and is associated with a nearly 4-fold higher likelihood of death or disability 1
  • The most common diagnostic error is failure to obtain a non-contrast head CT scan 1
  • Atypical presentations such as primary neck pain, syncope, seizure, or focal neurological deficits may not follow typical patterns and require thorough evaluation 1

• Warning Signs: Sentinel or warning headaches may precede major SAH in 10-43% of cases, typically occurring 2-8 weeks before overt rupture 1

When to Pursue Additional Testing

Even if the Ottawa SAH Rule suggests low risk, further evaluation is warranted for patients with:

• "Red flag" symptoms (thunderclap headache, new neurological deficits, altered mental status) 7
• Headache that awakens the patient from sleep
• Headache worsened by Valsalva maneuver
• Marked change in previous headache pattern
• New headache in patients over 50 years old
• Headache in immunocompromised patients or those with cancer
• Persistent headache following head trauma 7

The Ottawa SAH Rule represents the most validated clinical decision tool for ruling out SAH in headache patients, with perfect sensitivity across multiple studies, though its clinical utility is somewhat limited by low specificity.