NEW DATA SUGGEST LINK BETWEEN MILITARY SERVICE AND RISK FOR ALS
SAN FRANCISCO, CA — When the results of a new study on the link between military service and amyotrophic lateral sclerosis (ALS) were presented here in April at the AAN Annual Meeting, staff from several Congressional offices and the US Army were among those requesting more information. The finding of this new study – and several others before it – that men who serve in the armed forces may have an increased risk of acquiring ALS – continues to fuel debate: Are the findings scientifically valid and, if so, should they be used to justify a US government policy to pay for related medical expenses for all veterans who have ALS?
In this latest study, the investigators reviewed data on men who served in the military dating back to 1906. “Our findings suggest that military service is associated with an increased risk for ALS,” said Marc G. Weisskopf, PhD, Research Associate in the Harvard School of Public Health in Boston, MA, in an interview at the meeting. “The findings are preliminary, though. The next step is to find out why. Is military service associated with certain environmental exposures? Does deployment increase the risk? Our findings may open up options for getting at the root of the cause of ALS.”
Dr. Weisskopf collaborated with Alberto Ascherio, MD, DrPH, Associate Professor in the Departments of Nutrition and Epidemiology at Harvard School of Public Health.
Dr. Weisskopf noted that prior studies have suggested an increased risk for ALS among Gulf War veterans (Neurology 2003;61(6):750–756); and (Neurology 2003;61(6):730–731). In the current research, Dr. Weisskopf and his investigative team wanted to know whether military service prior to the Gulf War carried such risks.
SOURCE OF DATA
To get a sample large enough to extrapolate ALS data, the investigators used the American Cancer Society's Cancer Prevention Study II, a cohort that includes over 500,000 men surveyed by questionnaire in 1982. They then prospectively assessed the relationship between military service by following participant mortality for ALS deaths from 1989 through 1998 and then linking this database with the National Death Index.
The investigators calculated the relative risks by dividing the incidence of ALS among participants who reported military service by the corresponding incidence among participants who did not serve in the military. The data were adjusted for age and smoking status. The cohort consisted of 126,414 men who did not serve in the military and 268,258 who did.
Among the overall database of 394,872 men, 280 men – including veterans and non-veterans – died with ALS listed as the cause on the death certificate; 217 of them served in the military. The veterans entered service as early as 1906 and as late as 1982. Overall, the veterans had a lower mortality from all causes, a relative risk of 0.9; however, they were 1.6 times more likely than the non-veterans to die of ALS, a difference which had a statistical significance at the level of p = 0.004. This increased risk was similar for the Army, the National Guard, the Navy, and the Air Force. The investigators documented this increased risk of ALS among veterans in every five-year birth cohort from 1915 through 1939. However, they did not have sufficient data for those born before 1914 or those born after 1939; the latter group would have to be followed for several more years before they would be old enough to start experiencing ALS-related death, Dr. Weisskopf said.
“The increased risk of ALS among men serving in the military appears largely independent of the branch of service and the time period served,” Dr. Weisskopf said. “Therefore, the ALS risk for such men is apparently not specific to service during the Gulf War.”
“When assessing these findings, it's important to remember that the study is a retrospective cohort study with a military hypothesis,” said Carmel Armon, MD, Chief of the Division of Neurology at Baystate Medical Center in Springfield, MA, in a phone interview.
Dr. Armon, a neuroepidemiologist specializing in the epidemiology of ALS, added: “It's not a random sample. By design, such a study asks questions rather than answers them. We don't know how many hypotheses the authors had. Therefore, we can't interpret the incidence of ALS in military as being due to more than chance alone.”
Noting that the men with military service had a lower mortality rate than their non-veteran counterparts, he said that the reason for the increased incidence of ALS may be age-related. “People may be living longer,” he said. “Therefore, the increased risk of ALS wouldn't be due to military service, but would reflect a consequence of not dying from something else.”
In future studies of this hypothesis, or others, Dr. Armon said he would like to see mortality data for the population as a whole, as well as a multivariate analysis of all risk factors considered. “I have a fair number of questions regarding the findings, and I think neurologists should look at the findings with questions,” he said. “I would hope, as the data are analyzed further, that these questions would be addressed.”