Evidence-based guidelines on the use of diagnostic imaging in patients presenting with migraine have been developed by a multispecialty group called the U.S. Headache Consortium. The 14-member consortium led by the American Academy of Neurology (AAN) included representatives from the American Academy of Family Physicians (AAFP), the American Headache Society, the American College of Emergency Physicians, the American College of Physicians, the American Osteopathic Association and the National Headache Foundation. The guidelines are available at the AAN Web site (http://www.neurology.org) and at the AAFP Web site (https://www.aafp.org).

In addition to recommendations for neuroimaging, the five-part practice parameter includes sections on the methods for developing the guidelines, the treatment of acute migraine attacks, behavioral and physical approaches to treatment and drug prophylaxis of migraine. (See the accompanying table on page 1700 for the diagnostic criteria for migraine.) Using previous analyses by the Agency for Healthcare Research and Quality (formerly the Agency for Health Care Policy and Research) and by the AAN as a foundation for the guidelines, members of the consortium analyzed data from clinical studies on the diagnosis and treatment of migraine and formulated specific recommendations based on evidence and on consensus if data were insufficient.

Information from the U.S. Headache Consortium guidelines will be published in upcoming issues of American Family Physician as a series of five “Practice Guidelines.” The series begins with a summary of the guidelines for neuroimaging in patients with nonacute headache.

The recommendations in the neuroimaging guidelines are graded according to the strength of the evidence in support of the recommendation. Recommendations rated Grade A represent those that are based on multiple well-designed clinical trials that provide consistent findings relevant to the recommendation. Recommendations classified as Grade B are those in which some evidence to support the recommendation is available from clinical studies, but supportive evidence is not optimal. For example, there may have been few randomized trials. Grade C recommendations are those that were developed by consensus of the U.S. Headache Consortium in the absence of sufficient data from randomized control trials.

Aims of the Neuroimaging Guidelines for Headache

According to the consortium, the guidelines on neuroimaging were developed to provide evidence-based recommendations for diagnostic testing in patients with nonacute headache. The consortium members state that they examine three aspects related to neuroimaging: (1) whether there are findings in the history and physical examination that help identify which patients should undergo imaging because of a likelihood of significant intracranial abnormalities; (2) how frequently a cause of nonacute headache is found on computed tomography (CT) or magnetic resonance imaging (MRI) in patients with normal findings on the neurologic examination; and (3) the ability of CT and MRI to detect significant intracranial lesions in patients with nonacute headache.

Analysis of the Evidence on Neuroimaging in Headache

Data were examined from 28 studies that met criteria for inclusion in the meta-analysis; 22 of the studies were retrospective. The six prospective studies were not blinded.

The headache consortium found that most of the studies of patients with nonacute headache and normal findings on neurologic examination were conducted at referral centers, which could result in an overestimation of the prevalence of significant abnormalities in a primary care population. In addition, patients in most of the studies were selected for imaging, which may have skewed the patient population. Most of the studies did not include a description of the criteria for selection of patients for imaging studies. The consortium also found that evidence-based guidelines for any diagnostic testing other than CT or MRI could not be developed because of insufficient data.

The guidelines on neuroimaging include a discussion of the pieces of evidence from eight studies that reported sensitivity and specificity data on different clinical findings as they relate to the presence or absence of abnormalities on CT or MRI in patients with nonacute headache. Likelihood ratios were calculated by combining sensitivity and specificity to express the change in the odds of detecting a significant abnormality on CT or MRI if a certain sign or symptom was or was not present.

Likelihood ratios were derived for the following clinical findings (the number of studies and patients on which the likelihood ratios are based are in parentheses): any abnormality on the neurologic examination (five studies of 568 patients); any neurologic sign or symptom (two studies of 1,461 patients); a rapidly increasing frequency of headaches (one study of 350 patients); a history of syncope (one study of 350 patients); nausea (two studies of 450 patients); headache awakening the patient from sleep (two studies of 450 patients); a history of dizziness or lack of coordination (one study of 350 patients); a history of numbness or tingling (one study of 350 patients); the patient's report of “worst headache in my life” (one study of 350 patients); headache worsened by the Valsalva maneuver (one study of 100 patients); and abnormal skull radiographs (one study of 88 patients).

According to the guidelines, the presence of an abnormal finding on the neurologic examination significantly increases the likelihood of an abnormality on CT or MRI. Conversely, the absence of an abnormality on neurologic examination decreases the likelihood of a significant lesion on imaging studies. In one study of 350 patients, a significant increase in the odds of finding an abnormality on neuroimaging was seen in patients with a rapid increase in the frequency of their headaches, a history of dizziness or lack of coordination, a history of numbness or tingling, or a history of headache awakening the patient from sleep. However, the absence of such clinical features did not reduce the odds of an abnormality on CT or MRI.

Consortium members found three studies that described similarities between CT and MRI in patients with headache. However, each of these studies included fewer than 100 patients, with only a small proportion of patients undergoing both CT and MRI. On the basis of the limited data, the consortium members concluded that MRI may be more sensitive than CT in identifying clinically insignificant abnormalities, but MRI may be no more sensitive than CT in identifying clinically significant pathology.

Specific Recommendations for Neuroimaging

The consortium members advocate three consensus-based principles for diagnostic imaging: (1) testing should be avoided if it will not lead to a change in management; (2) testing is not recommended if the patient is not significantly more likely than a person in the general population to have a significant abnormality; and (3) testing that is not normally recommended may make sense in individual cases, such as in patients who are excessively worried about a serious problem as the cause of their headaches.

The specific recommendations for and against neuroimaging are as follows:

• Neuroimaging should be considered in patients with nonacute headache and an unexplained abnormal finding on the neurologic examination (Grade B recommendation). This recommendation is based on the finding that an abnormal neurologic examination increases the likelihood of intracranial pathology, such as brain tumor, arteriovenous malformation and hydrocephalus. The absence of abnormalities on neurologic examination reduces the odds of an abnormality on CT or MRI.

• Because of insufficient evidence, no recommendations are made regarding neuroimaging in the presence or absence of neurologic symptoms (Grade C recommendation). While the data suggest that headache worsened by the Valsalva maneuver, headache that awakens the patient, new-onset headache in older patients or progressively worsening headache increases the likelihood of significant intracranial pathology, the absence of such signs and symptoms is less reliable than their presence.

• Neuroimaging is not usually warranted in patients with migraine and normal findings on neurologic examination (Grade B recommendation). A lower threshold for CT or MRI may be applicable in patients with atypical features or with headaches that do not fulfill the definition of migraine (Grade C recommendation). These recommendations are based on the finding that an abnormality is unlikely to be found on CT or MRI in patients with migraine and a normal neurologic examination.

• Because of insufficient evidence, a recommendation regarding neuroimaging in patients with tension-type headaches cannot be made (Grade C recommendation). In two studies, no lesions were found in patients with tension-type headaches and normal neurologic examination.

• Because of insufficient evidence, recommendations regarding the comparative sensitivity of MRI and CT cannot be made (Grade C recommendation). The guidelines state that the greater resolution of MRI appears to be of little clinical importance in the evaluation of nonacute headache. No comparative data exist for the effectiveness of CT scanning with and without enhancement.

Future Research

The consortium points out that the prevalence of a significant intracranial abnormality is approximately 0.2 percent in patients with migraine and normal findings on neurologic examination. Because of insufficient data, such a prevalence is unknown in patients with tension-type headaches and a normal neurologic examination. In addition to research to provide data on the prevalence of intracranial lesions in patients with tension-type headaches, the guidelines state that research is needed to understand the prognostic importance of various clinical features, including syncope, nausea, “worst headache ever” and the frequency of headaches. Also, research is needed to determine the importance of risk factors such as diabetes, multiple sclerosis, hypertension, collagen disease, valvular heart disease, polycythemia and hyperlipidemia.