STOWE, VT—Navigating a differential diagnosis of headache is fraught with easily overlooked signs and symptoms that suggest a variety of serious underlying conditions. At the Headache Cooperative of New England’s 18th Annual Headache Symposium, David W. Dodick, MD, discussed what warning signs to detect and what pitfalls to avoid when attempting to confirm or eliminate a suspected diagnosis of dangerous headache.
Diagnosis Starts With a History and Examination
Ruling out dangerous headache “is something that takes years of experience and training to be able to do,” said Dr. Dodick, Professor of Neurology at the Mayo Clinic Hospital in Phoenix.
He emphasized that a patient who presents with and/or has a history of headache must be examined closely for symptoms or signs that suggest a possible secondary cause. Dr. Dodick devised an acronym, SNOOP4, that categorizes which of these signs a clinician should watch for when taking a patient history and performing an examination:
Systemic symptoms and signs, such as fever, myalgias, and weight loss, could point to giant cell arteritis or an infection; systemic disease, such as malignancy and AIDS, suggests metastatic disease or an opportunistic CNS infection.
Neurologic symptoms or signs raise suspicion for structural, neoplastic, inflammatory, or infectious CNS disease.
Onset, as in sudden-onset conditions (eg, thunderclap headache), could indicate an underlying stroke, subarachnoid hemorrhage, cerebral venous sinus thrombosis, reversible cerebral vasoconstriction syndrome, or arterial dissection.
Onset after age 50 suggests structural, neoplastic, inflammatory, or infectious CNS disease, or giant cell arteritis.
Pattern change (if there is a previous history) could point to progressive headache with loss of headache-free periods or be precipitated by valsalva, which suggests chiari malformation, structural lesions that obstruct CSF flow, or CSF leak. In addition, pattern change could involve postural aggravation that is worsened by either standing or lying down, suggesting intracranial hypotension from CSF leak or intracranial hypertension, or by certain neck movements and positioning, which might indicate cervicogenic headache. Lastly, papilledema, when present, raises suspicion for intracranial hypertension.
During an examination, determining onset by asking how the headache began is crucial. “It’s probably the most important question to ask, but the one that’s left out most commonly,” said Dr. Dodick.
What to Watch for on a CT Scan
If these signs or symptoms raise red flags that require testing and an MRI is contraindicated or not tolerated in a patient with headache, Dr. Dodick recommended ordering CT without contrast. Such a test is used to evaluate suspected rhinosinus pathology, skull fracture, or blood accumulation indicating a subdural, epidural, or subarachnoid hemorrhage. However, Dr. Dodick pointed out that “as a screen, a CT scan is almost never a definite test for a patient with headache, and yet in our emergency departments and in routine practice, it’s often used as a definite test.”
When CT is used to aid a suspected diagnosis of subarachnoid hemorrhage, for example, timing is a key factor, “because with time, the sensitivity of CT scanning decreases considerably, even as early as 36 hours after a subarachnoid hemorrhage,” he said. Another key factor for the clinician investigating subarachnoid hemorrhage is to watch for areas in the brain in which blood can accumulate, yet that are hard to spot on a CT scan or are misinterpreted as being due to something other than a ruptured aneurysm.
“It’s important not just to order the test, but know what to look for,” said Dr. Dodick, who devised the acronym PITS—parenchymal, intraventricular, truncal, and sulcal blood—to group subtle and easily missed danger areas of the brain. “Part of the problem why subarachnoid hemorrhage is so frequently misdiagnosed is that the CT is not done—which is usually not the case—or the CT is misinterpreted, or it’s interpreted as being negative/normal. When you see blood in the temporal lobe, for example, and it looks like an intraparenchymal hemorrhage, it could still be from an aneurysm.”
Scenarios for Other Tests
Dr. Dodick uses another acronym—PIN, which signifies disorder of intracranial pressure, infection, and neoplastic disease—to categorize three conditions that, if suspected, would prompt an MRI. “Basically, an MRI scan is appropriate if you’re evaluating a patient for something other than an acute subarachnoid hemorrhage or a skull fracture,” he explained.
Conditions such as intracranial hypertension and an assortment of neoplastic diseases, including parenchymal and extra-axial neoplasms, meningeal carcinomatosis, metastatic brain tumors, and pituitary lesions, can all be easily missed on a CT scan. As with a CT scan, however, knowing what to look for on an MRI scan is crucial.
With respect to investigating intracranial pressure, “you’re not just doing an MRI scan to rule out a mass lesion but to rule out some of the things that can mimic pseudotumor, [as well as detect] some signs of raised intracranial pressure,” Dr. Dodick said. In addition, when clinicians evaluate patients presenting with new chronic daily headache, the fact that low-pressure headaches are not always orthostatic and may require MRI testing is another point to be aware of, he stated. Other tests include a radionuclide cisternogram, used when patients with an orthostatic headache have otherwise normal MRI results, or cerebrovascular imaging, used to examine possible thunderclap headache.