Persian Gulf War veterans seem to have a slightly high incidence of the fatal neurological disease ALS, according to a six-month study of selected veterans' health records.

But so far, the number of cases is barely above what would normally be expected in men and women in the veterans' age range. Whether the excess is the result of something that happened in the gulf is uncertain, and will be hard to determine. The cause of ALS, also known as Lou Gehrig's disease, is unknown, and "extra" cases can occur in any population entirely by chance.

However, if the impression is upheld by rigorous research, ALS will be the first clear-cut physical ailment found in uncommonly large numbers in gulf veterans.

"We're convinced that we're either at the upper limits of expected cases or over the number" said Frances M. Murphy, a physician at the Department of Veterans Affairs headquarters involved in gulf war veterans' health issues.

In recent months, the VA and the Department of Defense identified 28 cases of ALS (the formal name is amyotrophic lateral sclerosis) among the 697,000 men and women who took part in the campaign against Iraq. The investigators suspect there are more cases that weren't found in the semiformal search. Epidemiological studies predict there should be 27 cases, over the course of seven years, in a population the size and age of the gulf veterans.

The VA will now try to find every gulf veteran with ALS, looking especially for people who may have been treated outside VA and military hospitals.

Within months of their return from Saudi Arabia in 1991, a small number of soldiers complained of tiredness, concentration problems, muscle aches, diarrhea and, in some cases, rash. The constellation of symptoms came to be called "gulf war syndrome."

Studies since then have shown that Persian Gulf War veterans are more likely to report certain symptoms than fellow soldiers who didn't go to the gulf. Also in higher prevalence are tropical infections (as expected); post-traumatic stress disorder (which is diagnosed entirely by interview); and multiple chemical sensitivity (a condition whose existence is disputed by many physicians). However, numerous studies have failed to find an increase of serious "objective" disease in gulf veterans.

There have been scattered reports during the last five years that an unusual number of gulf war veterans are suffering from ALS.

In ALS, the nerve cells in the brain and spinal cord that control muscles slowly deteriorate. Spontaneous twitching occurs early, and is eventually followed by profound weakness and atrophy of muscles. The average age at which the disease appears is 55; only half of patients live more than three years.

In January of this year, the VA convened a panel of three neurologists to review the medical charts of gulf veterans who had been diagnosed with the disease through June 1998. With the help of VA and Defense Department investigators, they both winnowed the list and added to it in a process that continued through last month.

Twenty of the 28 cases were found through the VA hospital system, and five through military hospitals. Three of the fatal cases failed to show up in a canvass of either system--a fact that one of the physician reviewers found highly significant.

"The fact that we are pushing the limits [of expected cases] just with this survey . . . makes me concerned that we haven't gotten the final number precise," said Benjamin Rix Brooks, a professor of neurology at the University of Wisconsin Medical School who works at the VA hospital in Madison. "If we can pick up 28 cases with this filter, then my fear is that there may be more cases out there if we look at other health care systems that might be providing care for veterans."

The ALS Association, a patient organization headquartered outside Los Angeles, also heard frequent rumors of an outbreak of the disease among gulf veterans. In its winter newsletter, the association asked any veteran of the armed services with definite or suspected ALS to contact it. About 1,200 did.

The vast majority are older veterans, but about 25 served in the gulf war. How many aren't on the VA's list is unknown. The association is now seeking permission from the respondents to give their names to the VA researchers so that question can be answered, said Mary Lyon, a vice president of the organization.

What constitutes the "expected" number of cases is a crucial, but slippery, part of any determination of whether there is excess ALS among gulf war veterans.

ALS is very rare in people between 21 and 50--the age group that encompasses virtually everyone who participated in operations Desert Shield and Desert Storm. Consequently, there are varying estimates of the disease's incidence in young age groups. The review panel averaged the incidence from nine large studies of ALS in civilians, and used that to predict the incidence among the gulf veterans.

As with many rare diseases, ALS sometimes seems to occur in clusters. In most of these instances, further study shows the rate to be within the broad range of what's expected.

Some "outbreaks" have been associated with war. For example, five cases occurred among former crew members of a Canadian destroyer in World War II, although no common cause was found. A large number of cases occurred among the natives of Guam after World War II--an unquestionable epidemic that's never been fully explained, but may have have involved the eating of neurotoxic cycad nuts during wartime food shortages.

Deciding whether a cluster of cases is a statistical fluke, or something else, is difficult in part because the cause of ALS is unknown. Almost certainly, there are numerous causes.

Cases sometimes run in families, so there appears to be an inherited form. A rapidly progressing form of ALS occasionally follows electrical injuries. A study of 174 cases occurring over four years in three Washington counties found that men with ALS (but not women) were twice as likely to report having been exposed to agricultural chemicals, compared to men without the disease. However, the exposures occurred more than 10 years before onset of the illness.

A study published last year looked at 1,538 deaths of commercial pilots and navigators in the United States between 1984 and 1991. Eight died of ALS, whereas only 3.4 deaths were expected in the group. This suggests--but doesn't prove--that aviators are at higher risk. (Five of the 28 cases in gulf war veterans occurred in people who worked in aviation.)

The VA's findings were greeted with both approval and bitterness by relatives of ALS sufferers.

"Good for them, they finally figured out how to count to 28," Denise Donnelly said of the VA researchers. "My brother and my family have spent the last three years making sure they paid attention to this."

Her younger brother, retired Air Force Maj. Michael Donnelly, flew 44 missions during the gulf war. He developed symptoms of ALS in the summer of 1995. He retired in 1996 and, at age 40, is severely disabled and unable to speak.

Both Denise Donnelly and her father, Tom Donnelly, a lawyer in South Windsor, Conn., believe some veterans with ALS may have been intentionally mislabeled in order to help them collect disability payments from the VA.

A veteran can claim his ALS is "service-related" only if the symptoms began while he was in uniform. If they arose years later, the claim is rejected. However, gulf war veterans can collect disability if they are disabled by an "undiagnosed illness" even if the symptoms appeared after leaving the military.

Robert Booker, a former Army National Guard mechanic in Alabama, had his ALS disability claim rejected by the VA in 1998, about six months after being diagnosed by a civilian doctor. His wife, Lynn, said a VA physician suggested she ask the civilian physician to change the diagnosis so he might qualify in the "undiagnosed illness" category. They didn't do this, she said, and have appealed the ALS rejection.

Like the Donnellys, the Bookers believe ALS came from toxic exposures--primarily poison gas and pesticides. "I think he was just given a toxic toddy," Lynn Booker said.

There is no evidence of widespread exposure to poison gas in the gulf. Pesticides and insect repellents, which bear some similarity to nerve gas, were fairly widely used.

Ultimately, the VA may decide to consider ALS (or other diseases) to be service-related for purposes of disability, even if the scientific evidence for a connection is marginal.