Are more lumbar punctures needed after CT scan?

Far too many emergency physicians are complacent about the use of lumbar punctures following a negative computed tomography (CT) scan to rule out subarachnoid hemorrhage in a patient with high-risk headache ("worst ever" or "thunderclap" headache), some experts say. Best practice guidelines clearly call for a lumbar puncture in such cases,1,2 but many physicians risk a catastrophic result and a malpractice suit by foregoing the procedure, they say.

Subarachnoid hemorrhage occurs in about one in 10,000 people, says Jonathan Edlow, MD, assistant professor of medicine at Beth Israel Deaconess Medi-cal Center in Boston.

Edlow says the research is crystal clear on the need for a lumbar puncture after a negative CT scan in a patient with high-risk headache, also defined as a headache of abrupt onset achieving maximal intensity within 10 to 30 seconds.

His own research confirms what others have suggested: A negative CT scan is insufficient to rule out subarachnoid hemorrhage and a lumbar puncture is the gold standard.1 Yet other research also shows that 78.4% of "rule out subarachnoid hemorrhage" patients with a negative CT scan do not undergo a lumbar puncture.3

So why the big disconnect? Edlow says one reason is that physicians are misinformed about the need for a lumbar puncture and the accuracy of CT scans. Add to that the fact that lumbar punctures can be difficult, time-consuming, and unpleasant for the patient, and soon you have a physician who decides the CT scan is sufficient to rule out subarachnoid hemorrhage.

Most patients being worked up for subarachnoid hemorrhage, in fact, don’t have subarachnoid hemorrhage, so the number of cases that any physician diagnoses by lumbar puncture is very small, Edlow says. "They don’t see it happen that often, and so they sort of devalue the lumbar puncture," he says.

Edlow says physicians are providing substandard care by not doing enough lumbar punctures. "We miss subarachnoid hemorrhages because we’re not doing spinal taps," he says. "It may not be an enormous number of cases, but it’s a significant number."

Part of the problem lies in basic human nature, Edlow says. Physicians don’t want to perform the lumbar puncture for a number of reasons, and the patient can be very resistant because of the pain, so it is easy for both to rationalize a decision to forgo the lumbar puncture.

Both may rely too much on the CT scan for a definitive diagnosis, says Robert Solomon, MD, FACEP, assistant professor of medicine at the West Virginia School of Osteopathic Medicine in Lewisburg and faculty member at the Ohio Valley Medical Center in Wheeling, WV.

"Patients think of CT scanning as high tech, state of the art, and they’re inclined to think that if anything bad is causing their symptoms, the CT scan will find it. And it’s easy for physicians who should know better to fall into the same trap," Solomon says.

Physicians look at papers that say the sensitivity for CT scanning for subarachnoid hemorrhage is well into the 90s, and when the CT scan comes back negative, they think they’re done, he says.

"What they fail to appreciate is that though the sensitivity is in the 90s overall, it’s not in the 90s for those for whom the diagnosis is most challenging," Solomon adds.

The CT scan will find the subarachnoid hemorrhage in the most obvious cases, but not necessarily in the patient with a smaller bleed and less dramatic symptoms, he explains.

Those are the patients most in need of a follow-up lumbar puncture, but physicians can convince themselves that the less dramatic presentation means it is safe to stop after a negative CT scan, Solomon says.

Pain management, ironically, also can get in the way of performing a lumbar puncture, Edlow and Solomon say.

Physicians often have treated the patients for pain before they go to the CT, and by the time they get back, they’re feeling better, Edlow says. However, the improvement with pain medication does not distinguish a subarachnoid hemorrhage from other causes of headache, he emphasizes.

"We properly treat these patients for pain, then we improperly conclude that because they’re feeling better, it can’t be a subarachnoid hemorrhage," Edlow says.

If clinical standards aren’t enough of a motivator, perhaps fear of a malpractice suit is. Edlow and Solomon say failure to perform a lumbar puncture can lead directly to a malpractice suit if the patient, in fact, has a bleed. Edlow says he has consulted on a number of such malpractice cases, and Solomon says he frequently warns fellow physicians about the risk.

Sometimes, of course, the patient simply refuses to undergo the spinal tap no matter how much the physician recommends it.

That decision can’t be held against the doctor, Solomon says, but there are ways to reduce that number of refusals. Emergency physicians can help patients accept the lumbar puncture by telling them up front that the CT scan helps diagnose the bleeding suspected in the patient’s brain but it can miss.

Explain to the patient that you already know you will need to do a lumbar puncture if the CT scan is negative; thus, the patient doesn’t go to the CT thinking it is a definitive diagnosis and then think the lumbar puncture is overkill.

Some patients still will resist after a negative CT, no matter what you tell them beforehand, Solomon says.

"Sometimes, I tell them that meningitis is one possible explanation, even though it actually is far down the differential, because they understand that meningitis is serious and they start wondering about that," he says. "It gets them to take seriously the idea that the CT may not have found everything."

References

1. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med 2000; 342(1):29-36.

2. Schull MJ. Diagnostic dilemmas and subarachnoid subtleties: What to do when the evidence gives you a headache. Can J Emerg Med 2002; 4(2).

3. Perry JJ, Stiell I, Wells G, et al. Diagnostic test utilization in the emergency department for alert headache patients with possible subarachnoid hemorrhage. Can J Emerg Med 2002; 4:5. 

Sources

For more information, contact:

  • Jonathan Edlow, MD, Assistant Professor of Medicine, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215. E-mail: jedlow@bidmc.harvard.edu.
  • Robert Solomon, MD, FACEP, Assistant Professor of Medicine, West Virginia School of Osteopathic Medicine, 400 N. Lee St., Lewisburg, WV 24901. Telephone: (800) 356-7836.