Column: OAS could be a sign of underlying pollen allergy

Brenda loves melons and cantaloupes. Until a few years ago, she could eat them without any problem.

Apparently in the last few years, she found out that whenever she ate these fruits, she developed intense itching of her throat and ears and sometimes swelling of her lips, tongue and throat. Once she had to go to a hospital emergency room because she felt her throat was closing. She is very much frustrated and needs some help desperately.

Oral Allergy Syndrome is a condition where people who are highly allergic to pollens develop symptoms of itching, swelling and hives involving lips, mouth, tongue and throat when they eat fresh fruits or vegetables. In the majority of such patients, the symptoms are confined to the mouth and throat. However, in 3 percent of patients, the symptoms could be more generalized, resembling a systemic allergic reaction (anaphylaxis).

Therefore, some doctors would like to call this condition Pollen Food Syndrome. This term, according to them, better explains the true nature of the problem.

What causes OAS?

The Oral Allergy Syndrome is a result of cross-reactivity between certain proteins (allergens) in fresh fruits or vegetables and other proteins in pollens from grasses, weeds and trees. It is mediated by IgE-antibodies directed against these cross-reacting proteins.

During pollen seasons (spring and fall), patients who have allergic rhinitis, allergy induced asthma and eczema develop IgE-antibodies to pollens. The amount of IgE antibody made increases during pollen seasons and declines during the rest of the year.

The resulting IgE gets fixed to the surface of mast cells and basophils - the cells that mediate immediate type allergic reactions. Theses cells primarily reside in the inner linings of eyes, nose, mouth, throat, gut, lungs and skin and around blood vessels.

Each IgE-molecule is directed against a specific allergen. For example, the IgE that is directed against Bermuda grass pollens is different from the IgE against cat dander and therefore will not recognize and react with cat dander.

When a specific IgE molecule on the surface of mast cells recognizes and combines with its specific allergen in pollens or foods, it triggers an allergic reaction. The resulting symptoms could be local at the point of contact (eye, mouth, nostrils, skin, etc.) or could be generalized (anaphylaxis) depending on the degree of allergy (mild versus severe), amount of exposure (small versus large) and site of exposure.

In Oral Allergy Syndrome, the structural similarity between certain allergens in fresh fruits and vegetables and pollens is so close that the body's immune system gets confused between the two and treats both of them in the same way.

For example, when a patient who is highly allergic to birch tree pollens eats fresh apples, he or she may develop itching, swelling and hives involving lips, mouth, tongue or throat. Other foods that may cross-react with birch tree pollens include pears, peaches, apricots, cherries, plums, nectarines, prunes, kiwi, carrots, celery, potatoes, peppers, fennel, parsley, coriander, parsnips, hazelnuts, almonds and walnuts.

Similarly, patients who are highly allergic to ragweed pollens may develop symptoms of OAS when they eat melons, cantaloupes, honeydews, cucumbers and avocados. Grass-allergic patients may react with peaches, celery, melons, tomatoes and oranges. Mugwort pollen-allergic patients may react with celery, apple, kiwi, peanut, fennel, carrots, parsley, coriander, sunflower and peppers. Alder tree pollen-allergic patients may react with celery, pears, apples, almonds, cherries, hazelnuts, peaches and parsley.

How does OAS manifest?

The symptoms of OAS could be mild or severe depending on how allergic the patient is to a particular pollen, the amount of cross-reacting food that is ingested, how ripe or unripe the fruit is and season of the year.

For example, some patients with OAS develop allergic symptoms only when they eat ripe bananas, whereas others do so only with unripe or partially ripe bananas.

Similarly, some patients with OAS can not eat certain fruits and vegetables during spring or fall but can eat the same food the rest of the year with much less problem. This wide variation in presentation makes OAS unique and interesting.

I'll discuss how OAS is diagnosed and how it is treated in next week's column.

Natarajan Asokan, M.D., F.A.A.P. is a board-certified allergist and immunologist and a board-certified pediatrician with more than 25 years of experience as a physician and eight years of experience as a practicing allergist and immunologist. He treats adults and children with various allergy and immunology problems. He can be reached at 1739, Beverly Ave, Suite 118, Kingman, AZ 86409; (928) 681-5800; Fax: (928) 681-5801; or www.trinityallergy.com.