Which Acute Headaches Do Not Require Investigation?

Abstract & Commentary

By Allan J. Wilke, MD, MA, Chair, Department of Integrative Medicine, Ross University School of Medicine, Commonwealth of Dominica. Dr. Wilke reports no financial relationship to this field of study.

Synopsis: Easily obtained clinical variables can identify patients at very low risk for subarachnoid hemorrhage.

Source: Perry JJ, et al. High risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache: Prospective cohort study. BMJ 2010 Oct 28;341:c5204; doi: 10.1136/bmj.c5204.

These investigators from canada designed a study to identify clinical characteristics that predict subarachnoid hemorrhage (SAH). Their second goal was to take these variables and develop a clinical decision rule. This prospective cohort study was conducted at six tertiary care, university teaching hospitals from 2000 to 2005. The inclusion criteria were: age ≥ 16 years; presentation to an emergency department complaining of a non-traumatic headache, which peaked in intensity within 1 hour of onset or syncope associated with a headache; and a Glasgow Coma Scale score ≥ 15. They excluded patients who had three or more similar headaches over the previous 6 months, patients referred from another facility with a confirmed diagnosis of SAH, patients who returned for reassessment of the same headache and who had already had a head computed tomography (CT) or lumbar puncture (LP) or both, and patients with papilledema, new focal neurologic deficit, history of cerebral aneurysm or SAH, brain neoplasm, or hydrocephalus. Each patient's data were collected on a standardized form.

Of 1999 enrolled patients, 130 (6.5%) had SAH. The remaining 1869 patients were actively followed for 6 months. Twenty (26) were lost to follow-up. The investigators were able to confirm that none of these patients had died in the 6 months after onset. The patients averaged 43 years (age range, 16-93 years) and were predominately female (60%). The headaches had their onset during exertion in 11.5%. Nineteen percent (19%) arrived by ambulance. The average time from the onset of the headache to its peak was 8.8 minutes. More than three-quarters described the headache as "the worst of my life." In 3% of cases there was witnessed loss of consciousness. More than a quarter experienced vomiting. Only 7% had neck stiffness with flexion and extension, although more than a third complained of neck stiffness or pain. The average blood pressure (BP) was 143/81 mm Hg. Most patients (83%) had head CT and/or LP. Twelve (12) patients died. Nine (9) cases of SAH were missed by the radiologists, but were picked up by positive results in cerebrospinal fluid. Head CT also picked up 48 (2.4%) other serious illnesses (e.g., transient ischemic attack, acute ischemic stroke, another type of hemorrhagic stroke, bacterial meningitis, hypertensive emergency, cerebral neoplasm). Most (81%) of the headaches were benign.

The researchers identified 26 possible predictor variables and, in univariate analysis, determined the strength of the association between them and SAH. They then developed multivariate models to predict SAH. They selected variables with good interobserver reliability, statistical significance, and clinical validity. The clinical rules were developed with the goal of 100% sensitivity. They used a sequential stepwise analysis, going from the most predictive variable to the least, until a low-risk group without any cases of SAH remained. In that way, a patient with any one of the variables would remain in the high-risk group and would need to be investigated. This resulted in three rules, each with four criteria:

Rule #1: Age > 40 years, complaint of neck pain or stiffness, witnessed loss of consciousness, and onset with exertion.

Rule #2: Arrival by ambulance, age > 45 years, vomiting at least once, and diastolic BP > 100 mm Hg.

Rule #3: Arrival by ambulance, systolic BP > 160 mm Hg, complaint of neck pain or stiffness, and age 45-55.

The authors excluded "arrival by ambulance" in the first rule specifically to address geographic areas where calling for an ambulance may be problematic. All three rules had 100% sensitivity. The specificity ranged from 28% to 39%. The investigation rates (those patients who received head CT, LP, or both) ranged from 64% to 74%.


A patient walks into your office complaining of the worst headache of her life. It started just a couple hours ago. This is a high stakes office visit. Many physicians, including me, would immediately send her for a head CT. Many physician educators, including me, have taught that a new onset headache in an adult is an indication for CT. This study says otherwise. I chose to review it because I am concerned that we are teaching our students and residents to ignore their clinical investigations and rely unnecessarily on technology.

This group of researchers had previously examined how Canadian emergency physicians managed patients with an acute headache.1 Not surprisingly, the physicians were able to distinguish SAH from other causes of headache solely on clinical grounds, but were loath to do so. I imagine that the results with U.S. emergency physicians would be very similar, considering the litigious nature of our society. This is not a diagnosis any of us would want to miss. On the other hand, the economics of testing every patient with a head CT and/or a lumbar puncture is substantial and subjects the patient to radiation or an invasive procedure. They also demonstrated that a negative head CT and a negative LP rule out SAH.2

About one patient of 40 had a serious illness that wasn't SAH. It is not clear whether any of these patients would have been excluded from investigation by any of the three rules, but I suspect not. The authors state, "For these patients, it was apparent from the documentation that physicians were concerned about the possibility of other pathology before they obtained results of imaging or lumbar puncture."

LPs are frequently performed after a negative head CT. Eight hundred fifty-four (854) patients in this study had both head CT and LP. An article from the United Kingdom in 2006 showed that for low-risk patients who had a negative CT, more than 1000 LPs would have to be performed to diagnose one case of SAH.3 In a study from Sweden published earlier this year, CT alone diagnosed 295 of 296 cases of SAH.4 Two hundred three (203) patients had a negative CT and a negative LP. In other words, LP diagnosed only one patient out of 499. Put down the spinal needle and back away from the patient.

It is important to remember that this study was performed on alert adults who were neurologically intact. Before these decision rules can be adopted, they will have to be independently validated in larger trials. (This group is currently performing its own prospective study of the rules.) If the rules are validated, as many as one patient in five could avoid investigation (the difference between the current rate of investigation of 83% and the low end of 64%) and the resultant exposure to radiation and post-LP headache. In the meantime, if a patient presents with any one of the seven findings from the three rules, the prudent physician should seriously consider SAH and perform a thorough investigation.


1. Perry JJ, et al. Attitudes and judgment of emergency physicians in the management of patients with acute headache. Acad Emerg Med 2005;12:33-37.

2. Perry JJ, et al. Is the combination of negative computed tomography result and negative lumbar puncture result sufficient to rule out subarachnoid hemorrhage? Ann Emerg Med 2008;51:707-713.

3. Coats TJ, Loffhagen R. Diagnosis of subarachnoid haemorrhage following a negative computed tomo-graphy for acute headache: A Bayesian analysis. Eur J Emerg Med 2006;13:80-83.

4. Cortnum S, et al. Determining the sensitivity of computed tomography scanning in early detection of subarachnoid hemorrhage. Neurosurgery 2010;66:900-902.