Background: Reported cases of ALS in young veterans of the 1991 Gulf War have suggested excess incidence.
Objective: To compare observed and expected incidence of ALS in Gulf War veterans diagnosed before age 45 years (young veterans).
Methods: Cases of ALS diagnosed from 1991 through 1998 were collected from military registries and a publicity campaign in late 1998. Diagnoses were established from neurologists' medical records using El Escorial criteria. Expected incidence was estimated from the age distribution of the Gulf War veteran population, weighted by age-specific death rates of the US population. Secular changes in nationwide ALS rates were assessed using calculations of the age-specific US population death rates from vital statistics data of 1979 to 1998.
Results: During 8 postwar years, 20 ALS cases were confirmed in approximately 690,000 Gulf War veterans, and 17 were diagnosed before age 45 years. All developed bulbar and spinal involvement, and 11 have died. In young veterans, the expected incidence increased from 0.93 cases/year in 1991 to 1.57 cases/year in 1998, but the observed incidence increased from 1 to 5 cases/year. The observed incidence was 0.94 (95% CI, 0.26 to 2.41) times that expected in the baseline period from 1991 to 1994 (4 vs 4.25 cases; p = 0.6); it increased to 2.27 (95% CI, 1.27 to 3.88) times that expected during the 4-year period from 1995 to 1998 (13 vs 5.72 cases; p = 0.006); and it peaked at 3.19 (95% CI, 1.03 to 7.43) times that expected in 1998 (5 vs 1.57 cases; p = 0.02). The magnitude of the excess of ALS cases over the expected incidence increased during the 8-year period (Poisson trend test, p = 0.05), and the increase was not explained by a change in the interval from onset to diagnosis or by a change in the US population death rate of ALS in those aged <45 years.
Conclusions: The observed incidence of ALS in young Gulf War veterans exceeded the expected, suggesting a war-related environmental trigger.