those studies, the Department of Veterans Affairs (VA) asked the National Academies to conduct an independent assessment of the potential relationship between military service and the later development of ALS. The population of interest to VA encompasses all veterans, not only veterans who served in a specific deployment (for example, veterans of the Gulf War). The National Academies assigned the project to the Institute of Medicine (IOM), which appointed a committee and charged it with evaluating the scientific literature on ALS in veterans. In addition, if an association were found to exist between military service and the later development of ALS, the committee might make recommendations that would help to identify risk factors for ALS that are relevant to military service.

In 2001, Secretary of Veterans Affairs Anthony J. Principi made a policy decision to provide disability compensation to Gulf War veterans who served in the Southwest Asia Theater of Operations during the period August 2, 1990-July 31, 1991, and who later developed ALS. Other US veterans with ALS do not receive disability compensation for their illness.

METHODOLOGY

The committee began its work by identifying the medical and scientific literature on ALS. PubMed, a database created and managed by the National Library of Medicine, was searched for studies on ALS in the veteran population. The articles relevant to the committee’s task were identified, and copies were obtained. Next, the committee assessed the studies for methodologic rigor and for evidence of association between service in the military and development of ALS. For information on possible ALS risk factors, PubMed was searched for studies on ALS in nonveteran populations and review articles on ALS (including articles on studies conducted in laboratory animals).

The committee framed its conclusion on the basis of categories that qualitatively rank the strength of the evidence of an association (described in Box S-1). The categories are adapted from the system of the International Agency for Research on Cancer for evaluating evidence of the carcinogenicity of various



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