Smoking Increases Seizures and Risk for ALS
By Allison Gandey
Medscape Medical News
November 25, 2009 — Physicians have new reasons to encourage patients to quit smoking. A new study has found that smokers are 2 times more likely to have seizures compared with nonsmokers. Another report says the habit may now be considered an established risk factor for sporadic amyotrophic lateral sclerosis (ALS).
"We observed a doubling in the risk of seizures and a modest nonsignificant increase in epilepsy in current compared with never smokers that appeared to be independent of stroke," report the investigators, led by Barbara Dworetzky, MD, from Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts.
Their work was published online November 18 in Epilepsia. Investigators used data from the Nurses' Health Study to evaluate 246 patients. The participants were women aged 25 to 42 years who had mailed in questionnaires about their lifestyle and medical history, including epilepsy and seizure activity.
After adjusting for stroke, brain tumor, hypertension, and other potential confounding factors, researchers observed a significant association between smoking and risk for seizure.
Smoking Status and Risk for Seizure
Smoking Status Relative Risk 95% Confidence Interval
Never 1.00 Reference
Past 0.98 0.58 – 1.66
Current 2.60 1.53 – 4.42
The risk for epilepsy or recurrent unprovoked seizures was modestly elevated with both past and current smoking. The relative risk was 1.46 and 1.27, but this was not statistically significant.
In another report, Carmel Armon, MD, from Tufts University, in Boston, and the Baystate Medical Center in Springfield, Massachusetts, outlined the link between smoking and ALS.
"Application of evidence-based methods separates better-designed studies from studies with limitations that may not be relied on," Dr. Armon said in a news release. "The better-designed studies show consistently that smoking increases the risk of developing ALS. Some findings suggest that smoking may be implicated directly in causing the disease," he said.
Established Risk Factor for ALS
Dr. Armon identified 28 studies. Of these, 7 articles met the inclusion criteria. Reporting in the November 17 issue of Neurology, he points out that only 1 study provided class 2 evidence, and another provided class 3 evidence. Both of these studies demonstrated an increased risk for ALS with smoking. The class 2 study showed a dose-response effect and risk decreasing with number of years since quitting smoking. The remaining articles provided class 4 or 5 evidence, which may not be relied on to draw conclusions.
Identifying smoking as an established risk factor for ALS has 3 implications, Dr. Armon said. "First and foremost, the findings provide a link between the environment and the occurrence of ALS, where none had been previously identified with this level of certainty," he noted.
"Since smoking has no redeeming features, avoidance may reduce the occurrence of ALS in the future, and since some of the mechanisms by which smoking causes other diseases in humans are understood fairly well, recognizing its role in the occurrence of ALS may help pinpoint the biological processes that initiate the disease," Dr. Armon said.
Nicotine is an excitatory neurotransmitter that enhances glutamate release. Glutamate plays a role in both epilepsy and ALS. Nicotine is a stimulant that may increase blood pressure and impair sleep. Smoking also causes tissue hypoxia from chronic carbon monoxide exposure.
Dr. Armon suggests that to change these conclusions, new evidence would need to be class 2 or higher.
The study linking smoking and seizures was supported by the National Institutes of Health and a research grant from the Epilepsy Foundation. Dr. Armon also received research support from the National Institutes of Health. He serves on the editorial board of Neurology, serves as a consultant to the Massachusetts Department for Public Health, and has given expert testimony related to risk factors and causation in ALS. Dr. Armon also receives royalties from eMedicine.com for updating electronic chapters. eMedicine appears on Medscape, and both are owned by WebMD.
Epilepsia. Published online November 18, 2009.
Neurology. 2009;73:1693–1698.
