WEDNESDAY, March 24 (HealthDayNews) -- In much the same way that allergies cause some people's bodies to overreact to usually harmless substances such as pet dander, people with chronic sinusitis have an immune system that overreacts to a common fungus.

That's the conclusion of a Mayo Clinic study presented March 23 at the American Academy of Allergy, Asthma and Immunology's annual meeting in San Francisco.

As the body attempts to destroy the fungus, the immune system damages the sinus membranes, which causes the symptoms of sinusitis, the researchers say. To combat the fungus and prevent the immune system reaction, the researchers tested the fungicide Amphotericin-B in a double-blind, placebo-controlled study.

"This is the first drug to pass a placebo-controlled trial to treat this common disease," says study co-author Dr. David Sherris, an associate professor and interim chairman of the department of otolaryngology at the University of Buffalo.

As many as 37 million Americans suffer from sinusitis every year, according to the National Institute of Allergy and Infectious Diseases. It is characterized by inflammation of the sinuses that can be caused by a number of factors, including a cold and allergies. The inflammation shrinks the nasal passages so mucus can't drain properly, leading to pain, discomfort and, potentially, infection.

"Sinusitis causes an enormous impact on people's quality of life," Sherris says. "It doesn't kill you, but it sure negatively impacts your life."

For this study, the researchers recruited 24 people with chronic sinusitis. Ten were given the antifungal medication and 14 were given a placebo. Both the medication and the placebo were applied using a nasal spray twice a day for six months.

After six months, the researchers compared computerized tomography (CT) scans from before and after treatment. They also did an examination at the start and end of the study using an endoscope, a special instrument with a light on the end that lets doctors see inside the nose. The researchers also asked the study volunteers to assess their symptoms at the beginning of the study, and then again after six months of treatment.

The percentage of mucosal thickening in the sinuses as seen on CT scans was reduced by nearly 9 percent for the group using the antifungal medication. In comparison, the placebo group experienced an average increase in mucosal thickening of 2.5 percent.

Sherris says that 70 percent of the fungicide group had an improved endoscopic exam versus none of the placebo group. He says 90 percent of those on the medication reported an improvement in symptoms while only 64 percent of the placebo group did. However, Sherris notes there was a flaw in the scoring system used to assess symptoms, and the symptom-relief differences aren't statistically significant.

"This drug decreases inflammation on both objective and subjective measures," Sherris says. People with chronic sinusitis would have to stay on this medication to keep symptoms from coming back, he adds.

"It's a chronic disease, like asthma in your nose. If you don't continue treatment, symptoms will come back," Sherris says.

He says eventual the goal would be to develop a medication that would blunt the immune system response to the fungus. In the meantime, he says, the next step is to test the antifungal medication in a large multi-center trial.

Dr. Richard Lebowitz, an otolaryngologist at New York University Medical Center, says the role of fungus in sinusitis is a controversial topic in medicine right now.

He says some physicians feel that all chronic sinusitis is due to an immune response to fungus, while others believe this only affects a subgroup of people with chronic sinusitis.

"In my mind, not all sinusitis patients are the same. Not all have a reaction to fungus," he says. But, he adds, the antifungal medication "may be useful in the right group of patients."

Sherris says because the medication is applied nasally, it doesn't get absorbed into the bloodstream. As a result, there were very few side effects, he says.

More information

To learn more about sinusitis, visit the American Academy of Otolaryngology - Head and Neck Surgery or the American Academy of Family Physicians.