The Case

A 38-year-old man presents to the emergency department with sudden onset of a severe frontal headache (HA) beginning two hours earlier while at work. He is feeling nauseated but hasn’t vomited. There was no loss of consciousness, fever, or neck pain. He reports that it feels like his previous tension HA, but it did not resolve with ibuprofen this time. His physical examination is normal.

Background

Headaches represent around 2 percent of emergency department visits each year. Of these presentations, 1 to 3 percent turn out to be a subarachnoid hemorrhage (SAH).^1–3

There are other causes of sudden onset of headache besides migraine and SAH. These include cough, exertion, and sexual intercourse (postcoital) as well as potentially life-threatening conditions like sinus thrombosis, vascular dissection, intracerebral hemorrhage, vasospasm, and aneurysmal subarachnoid hemorrhage.^4–7

Most sudden-onset headache cases are ultimately from benign, non-life-threatening causes like migraine HA. About 5 percent of SAHs are misdiagnosed on the first emergency department visit.⁸ Part of the reason is because 50 percent of SAH patients present with no neurologic deficits.⁹ Unfortunately, one-quarter of aneurysmal SAH victims die within one day, and 50 percent of SAH survivors never return to work.

Early identification of SAH reduces these adverse outcomes if subsequent neurosurgical interventions (coiling or clipping) occur emergently.¹⁰ Therefore, it is important to consider the possibility of aneurysmal SAH in emergency department patients presenting with severe headache.

The traditional method of working up a SAH has been non-contrast CT followed by a lumbar puncture (LP). A recent systematic review and meta-analysis has quantified the limitations of this approach.¹¹ A team out of Ottawa has developed a clinical decision instrument to try to limit the number of patients who need to be investigated further while not increasing the number of missed SAH cases.

Clinical Question

In patients with acute-onset HA, can the Ottawa SAH Rule decrease the number of patients who need further diagnostic evaluation without increasing missed cases of SAH?

Reference

Perry JJ, Sivilotti MLA, Sutherland J, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. CMAJ. 2017;189(45):E1379-E1385.

• Population: Alert patients 16 years and older with new acute severe nontraumatic headache that reaches maximal intensity in less than one hour of onset.
  • Exclusions: Patients with similar HA on three or more occasions over last six months, new neurological deficits, history of trauma or previous aneurysms, SAH, ventricular shunt, hydrocephalus, or brain tumors.
• Predictors: Positive Ottawa SAH Rule.
• Criterion Standard: CT + LP.
• Outcome: Performance of the Ottawa SAH Rule (sensitivity, specificity, likelihood ratios, and negative predictive value).

Authors’ Conclusions

“We found that the Ottawa SAH Rule was sensitive for identifying subarachnoid hemorrhage in otherwise alert and neurologically intact patients. We believe that the Ottawa SAH Rule can be used to rule out this serious diagnosis, thereby decreasing the number of cases missed while constraining rates of neuroimaging.”

Key Results

This prospective study enrolled 1,153 patients, of whom 67 (5.8 percent) had confirmed SAH. Five-hundred ninety potentially eligible patients were not enrolled, of whom 33 (5.6 percent) had confirmed SAH.

• Performance of the Ottawa SAH Rule:
  • 100 percent sensitive (95% CI, 94.6%–100%)
  • 13.6 percent specific (95% CI, 13.1%–15.8%)
  • Positive likelihood 1.16 (95% CI, 1.13–1.19)
  • Negative likelihood ratio 0.0 (95% CI, 0–0.5)
  • Negative predictive value 100% (95% CI, 96.9%–100%)

The Ottawa SAH Rule did not miss any cases of SAH. If the rule had been applied, 5 percent fewer patients (89 percent down to 84 percent) would have undergone additional testing (CT or LP).

Evidence-Based Medicine Commentary

External Validity: The six enrolling sites were the same hospitals that participated in the original Ottawa SAH Rule derivation studies. This could limit the external validity to other nonacademic or nonurban emergency departments.

Power and Precision: The study planned to enroll 1,200 patients with 75 cases of SAH to achieve near 100 percent sensitivity with tight confidence intervals. The study included 1,153 patients with 67 SAH cases. Therefore, the study was slightly underpowered, and the lower end of the sensitivity was 94.6 percent. This is less precise than they were hoping to achieve.

Shared Decision Making: One unmeasured obstacle to more efficient uptake of decision aids is the engagement of patients and families in the complex discussions around diagnostic evaluations. The science of developing patient decision aids is distinct from that of validating clinical decision rules and requires both a rigorous implementation strategy and sustainable funding environments.

Bottom Line: The Ottawa SAH Rule needs external validation, a meaningful impact analysis performed, and patient acceptability of incorporating this rule into a shared decision-making instrument before being widely adopted.

Case Resolution

The patient is not high risk by the Ottawa SAH Rule. After his HA resolves with IV metoclopramide, you explain the differential diagnosis of HA, including SAH. Your clinical gestalt is that the HA characteristics aren’t typical for SAH and more consistent with his previous tension headaches. You discuss the Ottawa SAH Rule and the fact that he has none of the high-risk criteria and his risk of SAH would be less than 1 percent. He is reassured and discharged home with instructions for follow-up.

Thank you to Christopher Carpenter, MD, MSc, of Washington University, who is the deputy editor of Academic Emergency Medicine and a faculty member of an emergency medicine and critical care course.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

References

1. Vermeulen M, van Gijn J. The diagnosis of subarachnoid haemorrhage. J Neurol Neurosurg Psychiatry. 1990;53(5):365-372.
2. Perry JJ, Stiell I, Wells G, et al. Diagnostic test utilization in the emergency department for alert headache patients with possible subarachnoid hemorrhage. CJEM. 2002;4(5):333-337.
3. Morgenstern LB, Huber JC, Luna-Gonzales H, et al. Headache in the emergency department. Headache. 2001;41(6):537-541.
4. Landtblom AM, Fridriksson S, Boivie J, et al. Sudden onset headache: a prospective study of features, incidence and causes. Cephalalgia. 2002;22(5):354-360.
5. Delasobera BE, Osborn SR, Davis JE. Thunderclap headache with orgasm: a case of basilar artery dissection associated with sexual intercourse. J Emerg Med. 2012;43(1):e43-47.
6. Pascual J, Iglesias F, Oterino A, et al. Cough, exertional, and sexual headaches: an analysis of 72 benign and symptomatic cases. Neurology. 1996;46(6):1520-1524.
7. Dodick DW, Brown RD Jr, Britton JW, et al. Nonaneurysmal thunderclap headache with diffuse, multifocal, segmental, and reversible vasospasm. Cephalalgia. 1999;19(2):118-123.
8. Vermeulen MJ, Schull MJ. Missed diagnosis of subarachnoid hemorrhage in the emergency department. Stroke. 2007;38(4):1216-1221.
9. Weir B. Headaches from aneurysms. Cephalalgia. 1994;14(2):79-87.
10. Schievink WI. Intracranial aneurysms. N Engl J Med. 1997;336(1):28-40.
11. Carpenter CR, Hussain AM, Ward MJ, et al. Spontaneous subarachnoid hemorrhage: a systematic review and meta-analysis describing the diagnostic accuracy of history, physical examination, imaging, and lumbar puncture with an exploration of test thresholds. Acad Emerg Med. 2016;23(9):963-1003.