Of the 1%-2% of total emergency room patients who complain primarily of headache, only a few have life-threatening secondary causes such as nontraumatic subarachnoid hemorrhage. However, the condition's seriousness and wide range of symptoms, combined with the positive outcomes seen in early surgical intervention, make accurate diagnosis of subarachnoid hemorrhage both difficult and crucial.
A recent New England Journal of Medicine article on avoiding pitfalls in diagnosing subarachnoid hemorrhage (January 2000, Vol. 32, No. 1 pp. 29-40) generated a lively round of letters to the editor in the May issue (Vol. 342, No. 19, pp. 1454-1456). The responses helped to clarify the optimal diagnostic approach presented in the article, and underscored the importance of performing CT whenever possible, even when neurological exams are normal.
According to retrospective studies, approximately 1% of patients presenting to emergency departments with headache had subarachnoid hemorrhage, according to article authors Dr. Jonathan Edlow and Dr. Louis Caplan from the departments of emergency medicine and neurology, respectively, of the Beth Israel Deaconess Medical Center in Boston.
"The initial hemorrhage may be fatal, may result in devastating neurologic outcomes, or may produce relatively minor symptoms," they wrote. "Despite the widespread availability of neuroimaging equipment, misdiagnosis of subarachnoid hemorrhage remains common, and it is an important cause of litigation related to emergency medicine."
In patients with subarachnoid hemorrhage treated at four Connecticut neurosurgical units in the 1990s, 25% initially received an incorrect diagnosis, the authors wrote. Although most of the patients were in good clinical condition initially, half of the patients who were incorrectly diagnosed worsened. Good or excellent outcomes at six weeks were seen in 91% who were correctly diagnosed, but only 53% of patients who were incorrectly diagnosed were as fortunate, according to the authors.
The classic symptoms of subarachnoid hemorrhage include sudden, severe headache that develops during exertion -- often described by patients as the worst headache of their lives. Other symptoms are a transient loss of consciousness, buckling of the legs, and vomiting. A physical exam may show retinal hemorrhages, nuchal rigidity, restlessness, diminished consciousness, and focal neurologic signs, the authors wrote.
Unfortunately, many of these symptoms are often absent, resulting in the high incidence of misdiagnosis. Worse, patients who are most likely to benefit from surgery are the ones most likely to be misdiagnosed, they added.
The authors attributed the high rate of misdiagnosis to three factors, including the failure to appreciate the spectrum of clinical presentation, failure to understand the limitations of CT, and failure to perform and correctly interpret the results of lumbar puncture.
Varying symptoms
From 20%-50% of patients report an unusually severe headache days or weeks before an episode of bleeding, and about half of all patients have episodes of minor bleeding with atypical features, they wrote. In addition, 34% of patients develop the condition during nonstrenuous activities, including 12% during sleep.
Some headaches are less intense and may resolve spontaneously, they wrote, but all tend to develop abruptly. Misdiagnoses include those of meningitis, influenza, or gastroenteritis when vomiting is present, or of cervical sprain or arthritis with symptoms of prominent neck pain. Diagnosis is further complicated as a result of head trauma that occurs when patients lose consciousness and fall.
CT's limitations
The authors recommend thin-slice (3 mm) CT scanning through the base of the brain, with the plane of scanning parallel to the hard palate to search for pools of blood indicative of hemorrhage. However, they cautioned, sensitivity decreases over time because subarachnoid blood sometimes clears rapidly. They cited spectrum bias as another of CT's limitations, in that alert patients are more likely to seek care than those with diminished mental status. CT remains the imaging method of choice, however, due to its wide availability and low cost, and because clinicians have wide experience in interpreting the results.
Lumbar puncture
The authors recommend lumbar puncture for patients whose clinical presentation suggests subarachnoid hemorrhage, yet whose CT scans are "negative, equivocal, or technically inadequate." Although it is rare in practice, lumbar puncture should be considered a cost-effective first strategy in patients with completely normal physical examinations, they wrote. High intracranial pressure is an important clue, and cerebrospinal pressure should always be measured.
Traumatic taps, which occur in up to 20% of lumbar punctures, must be distinguished from true hemorrhage to avoid risky diagnostic and therapeutic interventions, they wrote, and diagnoses are unreliable when based on the presence of erythrophages, erythrocytes, or on D-dimer levels in cerebrospinal fluid. However, the "presence of xanthochromia is the primary criterion for diagnosis of subarachnoid hemorrhage in patients with negative CT scans," the authors wrote.
Reaction and response
Two letters to the editor in the May 6 edition of the journal stressed the importance of CT in the initial diagnosis.
Drs. Clatterbuck, Tamargo, and Rigamonti from Johns Hopkins Hospital in Baltimore took issue with the authors' suggestion that lumbar puncture might be an acceptable first diagnostic procedure in patients with normal physical exams.
"We recommend continuing the practice of obtaining a CT exam in all cases of suspected subarachnoid hemorrhage, before a lumbar puncture....," they wrote. "A CT scan showing the presence of subarachnoid blood establishes the diagnosis and precludes the need for a lumbar puncture, which might precipitate rebleeding from a ruptured aneurysm." A procedure-related decrease in intracranial pressure or increase in systemic blood pressure could precipitate further hemorrhage with "catastrophic consequences," they wrote. Moreover, "unruptured aneurysms detected because of a traumatic tap should not be treated in the same manner as a ruptured aneurysm," they wrote.
Dr. Oguz Cataltepe of St. Luke's Roosevelt Hospital in New York City also weighed in, describing his experience with two patients with subarachnoid hemorrhage, both of whom presented with head trauma followed by headache.
"We would like to highlight the importance of CT findings in such cases," he wrote, adding that the character and distribution of blood in the images should be carefully assessed. "If the distribution of the hemorrhage is consistent with an aneurysmal rather than a traumatic source, an angiogram, an MR angiogram, or both should be obtained."
The authors responded that optimally, they do recommend noncontrast CT scanning as the first diagnostic study for several reasons, such as the fact that CT is fast, safe, painless, and, with positive results, precludes the need for a lumbar puncture. The low-cost lumbar puncture has not been evaluated clinically, they added, emphasizing that lumbar puncture should only be performed on patients with acute headache whose physical findings were "completely normal." Dr. Cataltepe's results with the two patients, they wrote, "highlight the importance of paying attention to all the details in evaluating patients with headache."
By Eric Barnes
AuntMinnie.com staff writer
May 16, 2000
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