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MILITARY DEPLOYMENT MAY RAISE RISK OF PARKINSON DISEASE

MIAMI BEACH—Men who were deployed during either World War II or the Vietnam War appear to be at increased risk of Parkinson disease (PD), a case-control study suggests.

In the study of 659 men aged 32 to 95 years, men who were deployed to World War II were twice as likely to develop PD, compared with those who did not serve, said Lorene Nelson, PhD, Associate Professor and Chief of the Division of Epidemiology in the Department of Health Research and Policy at Stanford University School of Medicine.

However, men who served at the time of World War II but were not deployed faced no increase in risk, Dr. Nelson reported here in April at the AAN Annual Meeting. Similarly, the risk of Parkinson disease was more than double among men who were deployed during the Vietnam War, but not among men who served at the time but were not deployed, she said.

Service during the Korean conflict, regardless of whether a man or a woman was deployed, was not associated with an increased risk of PD, she added. Overall, men who were deployed to one or more wars were 80 percent more likely to develop PD than those who never served, the study showed.

PART OF EPIDEMIOLOGIC STUDY

The case-control study is the first to examine the association of military deployment during US wars with the risk of developing Parkinson disease. It was part of a larger epidemiologic study the researchers conducted within the Kaiser Permanente Medical Care Program of Northern California to identify environmental and genetic risk factors for the disorder.

Many researchers have hypothesized that exposure to environmental chemicals, particularly pesticides, may increase the risk of developing PD, Dr. Nelson said. Also, in the last few years, studies have shown that the risk of developing amyotrophic lateral sclerosis is higher among veterans of the first Persian Gulf War and among men who have served in the military in general than among people who did not serve, she said.

STUDY PROTOCOLS

The new study included 300 men from the population who were newly diagnosed with PD during 1994 and 1995 and 359 men without Parkinson disease who were closely matched by age, race, and educational level.

Figure

In a case-control study of 659 men aged 32 to 95 years, men who were deployed to World War II were twice as likely to develop Parkinson disease compared with those who did not serve.

Among the findings:

  • The frequency of military service was similar for men with PD and those without the disease – about two-thirds of each group.
  • Thirty-one percent of the men with PD had been deployed in one of the three wars versus 21 percent of controls.
  • There was a significant 2.1-fold increased risk of PD among men who were deployed to World War II – 29 percent of men with PD had been deployed during World War II, compared with 19 percent of controls.
  • Five percent of men with PD had served in Vietnam versus 2 percent of controls. This translated to a 2.4-fold increased risk, although the finding was of borderline statistical significance due to the small numbers of men in the age group that had served in the Vietnam War, Dr. Nelson said.
  • Ten percent of men with PD had been deployed to Korea versus 8 percent of controls, a non-significant difference.

The design of the study precludes making conclusions about the factors associated with deployment that increase the risk of Parkinson disease, Dr. Nelson stressed.

EXPLAINING THE ASSOCIATED RISK

One possibility is that vaccinations, infectious agents, or other shared exposures are to blame, she said. “The fact that men deployed to either World War II or the Vietnam War were at increased risk for PD suggests that the risk of PD may be related to aspects of deployment other than a specific chemical exposure that was unique to one war or the other,” she told Neurology Today.

On the other hand, multiple factors could be at play, “with the herbicide Agent Orange responsible for the excess of cases seen in Vietnam, for example, and something else associated with the excess risk in World War II,” Dr. Nelson said.

Several studies have linked pesticide exposure to PD, she noted, but none specifically studied Agent Orange in this context. “We're just now beginning to develop contacts with industrial hygienists in the military and other experts knowledgeable about exposures,” she added. “There's a lot to learn.”

MORE STUDY NEEDED

Dr. Nelson called for future studies to confirm the findings and to investigate the deployment-related factors that may be responsible for an increased risk of PD among those who have served in US military conflicts.

“It will be many years before those who served in the Persian Gulf Wars are old enough to develop Parkinson disease, but the cohort of men who served in Vietnam will soon be aging into the period of greatest risk for developing PD, and studies to identify war-related exposures in this group are warranted,” she added.

The studies are methodologically challenging, however, due to the host of physical and psychological stressors associated with war exposure, including endemic infectious diseases, medical countermeasures such as vaccines, contaminated food or water, and chemical exposures such as organophosphate nerve agents, she said.

Nevertheless, Dr. Nelson's group is nearing completion of one such study – focusing on earlier-onset PD developing at or before age 60 years. “This will help us, especially in age groups that could have been deployed in Korea or Vietnam,” she said.

‘A GOOD STEP’

Eugene C. Lai, MD, PhD, Professor of Neurology at Baylor College of Medicine and Director of the Parkinson's Disease Research, Education, and Clinical Center at the Houston Michael E. DeBakey VA Medical Center, said that the current analysis is a good step toward finding out more about the possible association between wartime exposures and PD.

Dr. Lai said that he and other VA investigators have formed a collaborative group to perform the first large-scale study to investigate combat deployment and Parkinson disease.

“The VA system follows about 43,000 patients diagnosed with Parkinson disease a year, so we're interested in this question,” he said. As part of the study, which will include individuals who served in the military at the time of the Vietnam and Korean wars, “people will be asked direct questions about where they were deployed and whether they were exposed to anything they know of,” he said. “Then we will use information provided by the military about where certain chemicals were used and try to co-relate all that to deployment.”

“Now that we know more, we can really zoom in on some environmental conditions and see if they raise that risk,” Dr. Lai told Neurology Today. Among the exposures that will likely be investigated are fumes from petroleum products, the pesticide rotenone, Agent Orange, and radiation.

ARTICLE IN BRIEF

  • ✓ In the first case-control study to examine the association of military deployment during US wars with the risk of developing Parkinson disease, investigators reported that men who were deployed during either World War II or the Vietnam War appear to be at increased risk of Parkinson disease.