The studies used different methods yet arrived at similar results.
One study sought to identify all occurrences of ALS in the military after the start of the Gulf War, and found that those deployed to Southwest Asia (Saudi Arabia, Kuwait and other Arab Emirates, Turkey, or on the Red Sea) experienced almost twice the risk of ALS than those who were not deployed. Out of nearly 2.5 million military personnel, researchers verified 107 cases of ALS (40 deployed and 67 non-deployed). The total deployed population (696,118) was less than half the total non-deployed population (1,786,215).
"This study addressed the question, 'Is there a problem with excessive occurrence of ALS among Gulf War veterans?'," said lead study author Ronnie D. Horner, PhD, of the National Institute of Neurological Disorders and Stroke. "We found the answer to be yes."
Among deployed military, Army and Air Force personnel appeared to have a significantly higher risk than the other service branches, but all branches had an elevated risk. As a cross-check of the findings, the data were also evaluated under numerous "what-if" scenarios. The consistency of the findings gave the investigators the confidence to conclude that veterans of the 1991 Gulf War have a higher than expected risk of ALS, according to Horner.
The second study concentrated on age and found that the rate of ALS in young Gulf War veterans was more than two times greater than in the general population. Out of approximately 690,000 Gulf War veterans, 20 ALS cases were confirmed, 17 of whom were diagnosed before age 45. All of the cases had sporadic (non-familial) ALS.
"This study focused on people aged 45 or younger because there aren't enough people over 45 who served in the Gulf War and have ALS," said study author Robert W. Haley, MD, of the University of Texas Southwestern Medical Center at Dallas. "ALS is extremely rare in young age groups. Our findings suggest that some environmental exposure that these veterans had in the Gulf War greatly accelerated the ALS process so that it occurred at a much younger age."
Using national death rates, the study also determined that the rates of ALS in younger age groups remained otherwise stable during the 1990s. Thirteen of the 17 cases younger than 45 were diagnosed in the second half of the eight-year study period. This suggests that it took about four years for symptoms of ALS to start appearing, which would explain why the epidemic curve rose at the end, Haley said.
Both studies noted that further research should be done to identify environmental risks and other factors that could explain the elevated risk of ALS in Gulf War veterans.
An editorial in the same issue of Neurology cautions against uncritical acceptance of these results.
"While a twofold increase in risk may seem impressive, one needs to realize that this is based upon just a small number of cases," said editorial author Michael R. Rose, MD, of King's College Hospital in London. "Therefore the calculated risk may easily be changed either way if the methodology has any flaws."
Unfortunately Gulf War veterans are too small a cluster for reliably studying possible environmental triggers for ALS, according to Rose. The studies' subjects were in different branches of the armed service, deployed in different parts of the Gulf and possibly exposed - or not exposed - to several environmental triggers for illness, including ALS, which makes an accurate search for possible triggers very difficult.
Also known as Lou Gehrig's disease, ALS involves the degeneration of motor neurons which causes muscles to waste away. Approximately 20,000 Americans have ALS, which is usually fatal within five years after diagnosis. The Department of Veterans Affairs added ALS to the list of service-related disabilities in 2001.
The study by Horner et al was funded by the Department of Defense and the Department of Veterans Affairs. The study by Haley was supported by a grant from the Perot Foundation.
The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, autism and multiple sclerosis.
For more information about the American Academy of Neurology, visit its web site at www.aan.com.