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Every doctor knows that an extreme headache – "the worst headache of your life" – likely signals a brain hemorrhage, which calls for an immediate CT scan of the head to confirm a bleed.

But milder headaches challenge physicians to decipher if they are simply headaches or indicators of subarachnoid hemorrhage, a type of hemorrhage in the brain. Because they are difficult to detect, smaller hemorrhages are sometimes misdiagnosed as nothing more than a migraine. In such cases, CT scans may not be ordered and the patient is usually sent home.

Unfortunately, these are the patients with the most to gain from immediate treatment because smaller hemorrhages are usually treatable. Untreated hemorrhages sometimes hemorrhage again in the days or weeks after the first bleed, often leading to severe disability or death.

Now, new research by Columbia University Medical Center researchers calls for a lower threshold for administering CT scans to include people with milder brain hemorrhage symptoms, such as less severe headaches, nausea, vomiting, and prominent neck or back pain.

"Unlike prior studies that found the most common diagnostic errors were failure to interpret subtle CT or cerebrospinal fluid findings properly, we found that failure to obtain a CT in the first place was the most frequent diagnostic error," says Dr. Stephan A. Mayer, associate professor of clinical neurology and neurosurgery and director of the neuro-ICU at NewYork-Presbyterian Hospital. Dr. Mayer led the research, which was published in the Feb. 18 issue of the Journal of the American Medical Association.

Besides Dr. Mayer, the research team included Dr. Robert Kowalski, lead author and former research coordinator for the neuro-ICU; Dr. Jan Claassen, postdoctoral residency fellow in medicine; Dr. Kurt T. Kreiter, assistant professor of clinical neuropsychology (in neurology); Joseph E. Bates, research assistant; Noeleen D. Ostapkovich, associate research scientist in neurology; and Dr. E. Sander Connolly, associate professor of neurological surgery.

Subarachnoid hemorrhages are most often caused by aneurysms – sac-like protrusions of a blood vessel that can burst – or head injuries. Aneurysmal subarachnoid hemorrhages, which typically affect people in their 40s, account for 5 percent of all strokes and occur in 30,000 patients in North America each year. They result in serious impairment or death in 40 percent to 60 percent of cases. Cigarette smoking is the primary preventable risk factor for subarachnoid hemorrhage.

Published estimates of subarachnoid hemorrhage misdiagnosis vary widely, from 12 percent to 51 percent. Not surprisingly, misdiagnosed subarachnoid hemorrhage is reportedly one of the largest sources of lawsuits and malpractice settlements in the United States.

The CUMC researchers studied the results of 482 subarachnoid hemorrhage patients who were admitted to NewYork-Presbyterian Hospital between August 1996 and August 2001. The patients were interviewed at three months and one year after their hospitalizations to assess levels of disability and quality of life. The study is one of the largest analyses of misdiagnoses.

Fifty-six patients, or 12 percent, were initially misdiagnosed, including 42 of 221 (19 percent) of those with normal mental status when first seen by a doctor. In the study, migraine or tension headache (36 percent) was the most common incorrect diagnosis, and failure to obtain a CT scan was the most common diagnostic mistake (73 percent).

Among those who were initially misdiagnosed, neurological complications occurred in 39 percent before being correctly diagnosed, including 21 percent who bled again. Normal mental status, smaller hemorrhage, and right-sided aneurysm location were independently associated with misdiagnosis, although the importance of the right-sided aneurysm association is unclear.

Misdiagnosis was critical for the people who had normal mental status when they first saw a doctor for their headache. It was associated with a nearly four-fold increase in the likelihood of death at one year and with worse functional recovery and quality of life among survivors.

For the patients who were initially in good condition, the risk factors for being misdiagnosed were not being fluent in English, being unmarried, and not having more than 12 years of education.

Dr. Mayer and his colleagues were surprised to find that some of the patients had severe sentinel headaches preceding the one that made them seek medical attention. Sometimes these sentinel headaches, which can last for days or a week, are microbleeds or a stretching of the aneurysm. People who had sentinel headaches were also at risk for misdiagnosis, possibly because a doctor tends to view recurring headaches as a mild condition.

"Our message is: beware the patient who comes into the emergency room with a headache," Dr. Mayer says. "Even if the headache seems relatively benign, the mere fact that they've sought medical attention should be considered a danger sign."

The study was supported by a grant from the American Heart Association.

—Matthew Dougherty