Allergy Linked To Common Ear Infection Susceptibility

The study, by Dr. Robert F. Labadie of the UNC-CH School of Medicine, focused on a condition called otitis media with effusion, an inflammation of the middle ear accompanied by a buildup of sticky fluid behind the eardrum. Doctors consider this disease a serious threat to childhood hearing and development.

Because the new findings were observed in live animals, they may alter the treatment of children whose bouts with otitis media with effusion persist even despite surgical placement of tiny drainage tubes in the middle ear.

"This is the first time it has been shown dynamically and functionally that allergy inhibits drainage of effusion," said Labadie, an otolaryngology physician. "I think the next step is to take a drug that inhibits allergy inflammation, such as benadryl and its common derivatives, and see if that will help allergic children with recurrent otitis media with effusion.

September 14, Labadie reports his study to the American Academy of Otolaryngology annual conference in San Antonio. The study won the academy's 1998 Basic Science Award (2nd place). UNC co-investigators are Dr. Brian S. Jewett, Craig F. Hart, Dr. Jiri Prazma, and otolaryngology division head, Dr. Harold C. Pillsbury, who will be installed at the meeting as this year's academy president.

"There is some anecdotal and epidemiologic evidence that children with allergies have more episodes of otitis media," Labadie said. But until now, he points out, the mechanism by which food allergy makes children more sensitive to developing otitis media has only been assumed.

"There's a hypothesis that what you're allergic to causes the eustachian tube -- the natural passage that drains the ear into the back of the throat -- to become inflamed, to swell shut, and to fill with fluid," the researcher explained. "No one has ever shown that before, people have thought about it, and people have tried to study it histologically, looking at tissue samples of the eustachian tube under the microscope. We decided, for our study, not just to look at static histology or microscope shots. We wanted to look at a dynamic process, the actual draining of that tube."

In their experiment, the Carolina researchers used injections of ovalbumin, a protein found in egg white, to induce an allergy in laboratory rats. The protein was later used again to provoke a "subclinical" inflammation of the middle ear. This was done to mimic what might occur in children with food allergy who swallow something they are allergic to. The researchers then injected a strain of bacteria into the animals' middle ear cavity to induce an effusion. The eustachian tubes were then studied to determine how effectively they drained that effusion.

"It's well known that bacteria causes effusion," Labadie said. "And it turns out that the allergic rats that had been exposed to the allergen again couldn't drain the bacteria effectively because the Eustachian tube had swollen shut. This is the first time it's been shown in a living animal that they cannot effectively drain a middle ear effusion if they're allergic to something."

But the study also demonstrated that the disruption of drainage could be prevented with diphenhydramine (DPH), an antihistamine drug delivered directly into the middle ear. "Pretreatment with DPH caused a reduction of effusion volume with respect to time," the researchers state. They note that within six hours DPH-treated rats had a volume of middle ear effusion 1.5 times less than untreated animals.

According to Labadie, the new findings strongly suggest that antihistamines and related drugs may prove clinically effective for preventing as well as treating recurrent otitis media with effusion in allergic individuals. He cautions, however, that "most ear infections are not associated with allergy. This is a subset of patients, most of them children, with recurrent otitis media with effusion that has not been effectively treated with the standard techniques." Still, this "subset" may be sizeable. According to a 1989 landmark prospective study in the Greater Boston Area, 80 percent of children have at least one episode of otitis media by the time they are three years old. And 40% have at least three episodes.