By Julie Steenhuysen

CHICAGO, May 21 (Reuters) - Several U.S. soldiers exposed to a 2003 sulfur plant fire in Iraq have been diagnosed with a lung disorder that constricts small airways of the lung, making them unfit for duty, U.S. researchers said on Wednesday.

Doctors at Vanderbilt University in Nashville identified the illness after evaluating 56 soldiers stationed in Fort Campbell, Kentucky, who suffered from unexplained shortness of breath after exercise.

Lung function tests, chest X-rays and computed tomography, or CT, scans were normal in almost every case.

"We did open lung biopsies," said Dr. Robert Miller of Vanderbilt, who noted that surgery is a rather extreme diagnostic approach in such cases. "I just couldn't explain their abnormal pulmonary function."

Miller and colleagues eventually took lung samples from 31 of the soldiers who were referred to Vanderbilt, and 29 had a form of bronchiolitis, a condition that involves a narrowing of the small airways of the lung.

"The net result is it narrows the airway. In many cases it obliterates the airway," Miller said in a telephone interview.

Most of those diagnosed with bronchiolitis had breathed in sulfur dioxide released by the blaze at the plant near Mosul. The fire burned for almost a month and released more of the gas than most volcanic eruptions.

"Of the 31, 7 had biopsies and did not have this exposure, which says there are probably other inhalation exposures in Iraq that these guys are exposed to," said Miller. He and colleagues presented the findings at a meeting of the American Thoracic Society in Toronto.

STRIKE A MATCH

"Sulfur dioxide is what you get when you strike a match," Miller said. That might release 5 to 10 parts of sulfur dioxide per million. He said lab animals experience airway changes when exposed to 1 part per million.

"What these soldiers had was a lot of eye and skin irritation, which can be associated with levels as high as 100 parts per million," Miller said.

He said the Iraqi sulfur plant fire in 2003 was the largest ever human-made release of sulfur dioxide gas and was 100 times greater than the release from the Mount St. Helens volcanic eruption in 1980.

What was puzzling about the soldiers is that they had pulmonary function scores in the normal range, but Miller thinks that may simply reflect their high level of fitness prior to exposure.

All of the soldiers evaluated were physically fit at the time of deployment. But when they returned, none met physical training standards.

"One of the reasons we picked it up is you have these guys who are expected to maintain this level of training and all of a sudden they fall off the curve," he said.

All of the soldiers but one have been declared unfit for duty and have a service-connected disability.

"There isn't any good treatment. At this point, I've followed several soldiers now for almost three years, and they are not getting any better," Miller said.

In adults, bronchiolitis is typically associated with organ transplantation, toxic inhalation, infection and rheumatoid arthritis. Usually, doctors diagnose it based on a patient's history, X-ray and lung function tests.

For soldiers who have served in Iraq and have unexplained shortness of breath, Miller thinks doctors may need to take the extra step of ordering a biopsy.

"I believe this is a qualifying risk factor," he said. (Editing by Anthony Boadle)

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