Amyotrophic lateral sclerosis among 1991 Gulf War veterans: evidence for a time-limited outbreak.

BACKGROUND: In follow-up to recent reports of an elevated risk of amyotrophic lateral sclerosis (ALS) among 1991 Gulf War veterans, we analyzed the distribution of disease onset times to determine whether the excess risk was time limited.

METHODS: This secondary analysis used data from a population-based series of ALS cases identified between 1991 and 2001 among the 2.5 million military personnel who were on active duty during the 1991 Gulf War. Annual standardized incidence ratios (SIR) were calculated for all cases and for those with disease onset before age 45 years.

RESULTS: Forty-eight of 124 cases occurred among those deployed to the Persian Gulf region during the war. The annual SIR for deployed military personnel did not demonstrate a monotonically increasing trend for either all cases (chi(2) = 0.11, d.f. = 1, p = 0.74) or for cases under 45 years of age at onset (chi(2) = 2.41, d.f. = 1, p = 0.12). The highest risk was observed in 1996, declining thereafter. Among military personnel who were not deployed to the Gulf region, the level of risk remained fairly constant during the 11-year period.

CONCLUSIONS: The excess risk of ALS among 1991 Gulf War veterans was limited to the decade following the war.