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.
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.
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?
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).
“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.”
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.