Occupational Exposures and Risk of ALS

August 30, 2018

If your patient is a construction worker, bus driver, gas station attendant, or mechanic, take notice: “This type of exposure deserves more attention and study as we work to develop a better understanding of what causes ALS,” notes the author of a recent study.

On-the-job exposure to diesel exhaust may increase the risk of amyotropic lateral sclerosis (ALS), and the risk may be greater for those with higher levels of exposure, according to a study by Dickerson and colleagues.[1]

ALS, also known as Lou Gehrig disease, is a rare neurological condition that gradually affects walking, talking, and other voluntary muscular activities. Currently no cure exists, and the condition progressively leads to death, usually from respiratory failure. The cause of ALS has yet to be identified.

“There is some suggestion from previous studies of occupation that workers in jobs with higher exposure to diesel exhaust may have a higher risk of ALS. However, no studies have directly looked at the relation between diesel exhaust exposure during different time points in life and ALS,” first author Aisha Dickerson, PhD, of Harvard T.H. Chan School of Public Health (Boston, MA), said in a press release by the American Academy of Neurology.[2]

In the study, researchers used the Danish National Patient Registry to identify 1639 people diagnosed with ALS between 1982 and 2013.[1] The average age of participants was 56. Each case was matched by birth year and sex to 100 healthy controls identified in the Danish Central Person registry. Employment history since 1964 came from the Danish Pension Fund. Researchers estimated cumulative diesel exhaust exposure for 5 and 10 years before the diagnosis of ALS, or a similar time period in controls. Estimated exposure was based on potential risk for certain types of jobs, such as construction workers, bus drivers, and gas station attendants. Results were adjusted for socioeconomic status and region in Denmark where participants lived.

Key results:
• 20% increased odds of ALS in men exposed to diesel exhaust 10 years before ALS diagnosis, vs no exposure during this time period
• Higher exposure linked to higher odds of ALS:
• 45% increased odds of ALS in men with >50% probability of diesel exhaust exposure 5 and 10 years before diagnosis
• No link between diesel exhaust exposure and ALS in women

The study has several potential limitations. Due to its design, results can only show an association but cannot prove that diesel exhaust exposure increases the risk of ALS. Also, the study used estimates of occupational exposure to diesel exhaust and could not directly measure exposure, which could have affected results.

“This type of exposure deserves more attention and study as we work to develop a better understanding of what causes ALS. Importantly, the general population can be exposed to diesel exhaust from traffic pollution. Understanding whether that exposure increases ALS risk is also an important question to pursue,” Dickerson concluded in the AAN press release.[2]

Take home points
• Preliminary study found that occupational exposure to diesel exhaust may increase the risk of developing ALS 5 to 10 years later
• The risk of ALS increased with higher levels of exposure to diesel exhaust
• Exposure to diesel exhaust was linked to increased odds of ALS in men but not in women

References

1. Dickerson AS, Hansen J, Gredal O, Weisskopf MG. Amyotrophic lateral sclerosis and exposure to diesel exhaust in a Danish cohort. Am J Epidemiol. 2018;187:1613-1622.

2. American Academy of Neurology. Study suggests risk of ALS increases with more exposure to diesel exhaust. https://www.aan.com/AAN-Resources/Details/press-room/press-room-archives/february-27-2018.

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Occupational Exposures and Risk of ALS

Veronica Hackethal, MD