Allergic Rhinitis (Hayfever)
March 25th, 2010 by The Doc
As springtime arrives, so do seasonal allergies. The form of seasonal allergy familiar to most people is allergic rhinitis, commonly known as “hay fever.” This condition is characterized by a constellation of signs and symptoms, including runny nose, itchy throat, sneezing, nasal and sinus congestion, and sometimes conjunctivitis.
Allergic rhinitis is a true atopic condition: it is driven by an exaggerated IgE-mediated immune response (a type I hypersensitivity reaction, for those who keep track of such things). Whenever the appropriate foreign antigen binds to IgE, and thence to IgE receptors on the mast cells of susceptible persons, the mast cells release copious amounts of histamine, which is a molecule that dilates blood vessels, increases capillary permeability, triggers neuronal reflexes, increases salivary and mucoid secretions, and constricts smooth muscles in the airways.
Thus, histamine’s effects on various tissues are responsible for all of the signs and symptoms that we normally associate with hay fever.
Allergic rhinitis is typically caused by exposure to tree pollens in the spring, grass and weed pollens in summertime, and weed pollens in autumn. Fungal spores can also trigger symptoms of allergic rhinitis. The instigator of a given individual’s symptoms will vary according to that person’s specific sensitivities, the region where he or she lives, and the time of year.
Perennial rhinitis, which affects some unfortunate individuals on a year-round basis, is usually caused by ongoing exposure to indoor antigens (dust mites, mold spores, pet dander, etc.) or sensitivity to plants that pollinate in a sequential fashion – or a combination of these factors.
Allergic rhinitis often coexists with other allergic conditions, such as atopic dermatitis or asthma. In the case of the latter, it isn’t clear whether asthma and allergic rhinitis are both simultaneously triggered by the same agent, or if rhinitis serves to trigger bronchospasm, with its attendant signs and symptoms.
Diagnosis of allergic rhinitis is usually straightforward: a person’s history, clinical signs, and response to empiric antihistamine treatment will tell the tale. However, if a patient doesn’t improve with antihistamines – or if desensitization therapy is planned – skin tests can clarify sensitivities to specific allergens (cockroach, dust mite, cat, dog, horse, mold, hay, etc.).
If a symptomatic person’s skin tests are negative – that is, they reveal no sensitivity to any of the tested allergens – then he or she may be suffering from a non-allergic form of rhinitis: vasomotor, gustatory, drug-induced, hormonal, or infectious rhinitis; or a special form of rhinitis called “non-allergic rhinitis with eosinophilia (NARES).”
Treatment of allergic rhinitis is aimed at alleviating symptoms and, whenever possible, reducing exposure to offending allergens. Eliminating some sources of allergens may be possible (removing pets from the home, for example); usually, though, exposure-reducing measures are designed to merely limit the allergen load: keeping lawns mowed so they don’t pollinate; eliminating weeds around one’s home; placing mite-proof covers on mattresses and pillows; fumigating for roaches; frequent vacuuming, using vacuum cleaners that employ HEPA filters, etc.
Oral antihistamines and decongestants often furnish sufficient relief for individuals whose symptoms are limited to a few weeks of the year. Nasal corticosteroid or mast-cell-stabilizing sprays are frequently added to oral therapies. Nasal saline drops or sprays are useful adjuncts to any therapy; by helping to loosen thickened mucous and moisten nasal membranes, this inexpensive modality can significantly alleviate symptoms.
Montelukast (Singulair) and zafirlukast (Accolate), medications that interfere with the activity of leukotrienes (yet another inflammatory molecule), have proven beneficial for some people.
When symptoms are severe or prolonged, desensitization therapy may be useful. Following skin tests to determine a patient’s specific sensitivities, an injectable serum is formulated and administered beneath the skin in gradually increasing doses. The idea behind this therapy – some would say it is homeopathic in its approach – is to initially expose the immune system to tiny amounts of an allergen and gradually increase that exposure in an effort to “fool” the immune system into accepting the allergen. Actually, the reasoning behind such therapy is sound: incremental doses of an allergen may induce the production of different classes of antibodies (IgG, for example) that will bind the allergen before it can attach to the IgE that leads to mast cell degranulation and histamine release. This approach may also encourage the production of cytokines or white cells that inhibit the allergic response.
Whatever treatment is eventually brought to bear on an individual basis, anyone who has ever suffered from hay fever will probably acknowledge that no treatment is 100% effective.
Indeed, most allergic rhinitis sufferers will admit that they can’t wait until their season of personal travail has passed and they can get on with their lives…until next year.