WASHINGTON (AP) - A Pentagon-financed study concludes that a drug given to U.S. troops during the Persian Gulf war to protect against a nerve gas cannot be ruled out as a possible cause for what has come to be known as Gulf War syndrome. Defense Department officials were presenting the 385-page review of scientific literature on the drug pyriostigmine bromide, or PB, at a news conference Tuesday. Prepared By Beatrice Alexandra Golomb of Rand Corp., a California think tank, the study says PB "cannot be ruled out" as a cause of lingering illnesses in some veterans of the Gulf War.