ARTICLE IN BRIEF
A new analysis of data on driving and seizures questions whether epilepsy patients who have auras, which warn of an impending seizure, have fewer driving accidents.
How do neurologists determine if it's safe for a patient with epilepsy to drive? Criteria for making the decision are unclear, and state laws on the question vary.
In an effort to better understand the factors that influence driving impairment in people with refractory epilepsy, a research team at Yale University pulled data on driving and auto accidents from a large database of patients undergoing assessment for epilepsy surgery.
The researchers uncovered data that conflicts with earlier assumptions about safe driving in people with epilepsy. They presented their findings at the American Epilepsy Society annual meeting in Seattle this month.
“Many neurologists believe that if people have an aura it would give them time to pull off the road and stop driving,” said Hal Blumenfeld, MD, PhD, a professor of neurology, neurobiology and neurosurgery at Yale and director of the Yale Clinical Neuroscience Imaging Center. “But we found that people with auras do not have fewer driving accidents. Aura is not protective, not even if it is a long aura.”
He added, “It is so important to have the privilege of driving, but the consequences can be serious for patients with refractory epilepsy. Some states leave the decision of when to resume (or begin) driving up to the neurologist, but there is just not enough information to provide doctors or patients with guidance about who should be able to drive and when. We've been working on common sense, but we are still in the dark.”
The new analysis came about in response to a dearth of good data, according to Vineet Punia, MD, who came to Yale to do research as part of an elective.
“No single study had looked at all the various seizure-associated features and their impact on motor vehicle accidents,” said Dr. Punia, who is now an epilepsy fellow at the Cleveland Clinic. Three studies were conducted that were not specifically designed to look at driving, but their data were conflicting, he said. Two studies suggested a possible benefit of auras as a signal to pull over, but the third found auras had no protective benefit.
The Yale team wanted to design a larger study to answer the question, so they combed through hundreds of surveys comprising the Multicenter Study of Epilepsy Surgery database, an observational cohort of 565 surgical candidates recruited from June 1996 through January 2001 at seven centers around the country. The study was conducted to examine predictors of seizure outcomes after epilepsy surgery; as part of their evaluation for surgery, the patients were asked whether they had experienced a seizure while driving.
The researchers divided patients who reported having seizures while driving into two groups: those whose seizure led to an accident, and those who did not have an accident. Then, they identified the type of seizure disorder and whether the patient reported having auras that preceded the seizure.
ANALYSIS OF DATA
Of the 553 patients surveyed, 215, or 38.9 percent, reported having a seizure while driving, Dr. Punia reported; 74 had not had accidents, while 141 reported an accident at the time of the seizure. The two groups were matched on age, sex, seizure localization, medication history, and history of aura. The researchers found no differences in reports of aura between the two groups (OR=0.89, 95% CI 0.49-1.61, p=0.76).
They also analyzed the type of seizure and the duration of the aura. Patients who had a history of complex partial seizures (OR=1.83, 95% CI 1.14-7.09, p=0.029) or reported having experienced at least one complex partial seizure per month in the last three months (OR=2.52, 95% CI 1.22-5.21, p=0.01) had much greater odds of being involved in a seizure-related motor vehicle accident.
The length of the seizure did not seem to affect the risk for a motor vehicle accident, but patients with a longer postictal period (of more than one minute) had a greater likelihood of having a driving accident related to their seizure (OR-2.53; 95% CI 1.04-6.19; p=0.05). Surprisingly, they also reported that convulsions and serious disruptive automatism did not lead to more seizure-related car accidents.
What does this mean for patients? The researchers said that neurologists and lawmakers must rethink current recommendations about driving with epilepsy.
For the past 20 years, the American Academy of Neurology and the American Epilepsy Society have proposed using “consistent and prolonged auras” as a favorable modifier when considering eligibility for a driver license, Dr. Blumenfeld said. The recommendations were based on consensus statements, sample statutory provisions, and model regulations regarding driver licensing and epilepsy.
However, “our findings question the assumed protective benefit of reliable auras against motor vehicle accidents,” Dr. Blumenfeld said.
Even patients who said they believed their aura was reliable enough to protect them fared no better than those without aura. “The presence of aura is providing a false sense of safety,” Dr. Punia said. “We need more prospective studies. What we thought was true about aura as a protective factor is not true.”
“We have to look for other factors that might provide more guidance for us to make recommendations to patients about driving,” Dr. Blumenfeld said. He added that there is evidence from their studies that seizure type may be a predictor for who should or should not drive.
In a separate trial, a research team at Yale, also headed by Dr. Blumenfeld, looked at the effects of clinical and sub-clinical epileptiform discharges on driving. Previous studies have suggested that subclinical epileptiform discharges (SEDs) might exert an additional and independent subtle effect on transient cognitive processes such as alertness and mental speed, but it was not clear whether these SEDs might pose a threat to driving safety, the researchers wrote in the study abstract.
For their study, they asked patients who were undergoing continuous video-EEG monitoring in the Yale epilepsy center to “drive” using a portable, computer-based driving simulator, complete with brakes, gas, and a steering wheel. They compared baseline driving performance for each participant to detect changes in car velocity, steering wheel movement, accelerator position, and crash rates.
At the AES meeting, the researchers presented data based on 30 seizures in 20 patients and 100 SEDs in 19 patients. They found that people with longer seizures and seizures that led to a loss of consciousness had a greater likelihood of crashing in the simulated driving setting than those with other types of seizures.
“It looks like impaired consciousness during a seizure is the most important predictor for risk of an accident while driving,” Dr. Blumenfeld said.
With this study design, “we can begin to answer questions that we just do not know by asking people to fill out a survey,” he said. “Are there certain driving activities that are dangerous? This is a way of obtaining solid information.”
Dr. Blumenfeld noted that two patients in the study had tonic-clonic seizures and both had accidents. “Right now, we can say that people who lose consciousness during a seizure or have serious impairments in motor function should not drive unless their seizures are controlled with treatment,” he said.
The effects of SEDs on driving were less clear and will need further investigation, he added. Patients who lost consciousness were asked whether they remained responsive during the seizure and their answers were not always accurate, he pointed out.
Commenting on the two driving studies, Kimford J. Meador, MD, a professor of neurology and neurological sciences at the Stanford Comprehensive Epilepsy Center and Stanford University School of Medicine, noted that there are no state driving laws that tie aura into decisions about whether or when someone should be allowed to drive.
“The state laws only care about loss of awareness or loss of consciousness,” he said. In addition, state policies vary as to how long patients have to be free from seizures without loss of awareness or loss of consciousness before they can drive again. The seizure-free intervals can be anywhere from three to 12 months.
Dr. Meador noted that the states have never taken auras into account when they make these laws, which do not just apply to epilepsy patients but also to anyone who has lost consciousness because of an illness. However, he believes that the information is important for clinicians in counseling their patients about driving.
Stephan Eisenschenk, MD, an associate professor of neurology at the University of Florida, has studied epilepsy in driving behavior for years. He contends that seizure type may be a factor to consider in determining driving capacity.
“We have found that complex partial seizures and a longer postictal state may contribute to an increased risk of accidents,” he said, and impaired consciousness may be a key factor.
During the prolonged postictal period, the cortical pathways responsible for maintaining vigilance and visual spatial processing on the road may be disrupted, compromising the ability to drive safely, he explained.
“Driving depends on effortless [mental] processing, which develops following extended and consistent practice. If the seizures are focal in a region of the brain, such as the temporal lobe, which is mainly important for short-term memory, then driving will not be interrupted. I have had patients who could drive during that kind of seizure,” he said.
Dr. Eisenschenk noted that other studies have suggested that approximately 30 percent of patients with poorly controlled seizures continue to drive, despite having a restricted license. His studies have also questioned the assumed protective benefit of reliable auras against motor vehicle accidents. There is a dearth of reliable data on auras and driving, he said.
“Driving is one of the most common concerns among our epilepsy patients,” said Allan Krumholz, MD, a professor of neurology at the University of Maryland School of Medicine. “We still don't know exactly who is always safe to drive and who isn't safe to drive, but there are many important factors that predict who will have a recurrent seizure and therefore have an increased risk of a motor vehicle accident if they drive. The factor proven to be the best predictor is the length of time people are seizure-free.”
He said that the current study should be replicated in other groups of epilepsy patients. The survey data, he noted, are based on self-reports from patients who are scheduled for epilepsy surgery and may not represent most epilepsy patients.
But, he added, neurologists have used information about aura to shorten the time period that a person is restricted from driving. “We should now be cautious about doing that.”
EXPERTS: ON DRIVING AND SEIZURE RISK