Since these conditions may be aspects of a single disease, coordination of therapies is essential for optimal outcome. Options include new roles for leukotriene inhibitors, new antihistamines, and an anti-IgE antibody aimed at bridging the airway inflammation characteristic of both conditions.
There is a growing clinical consensus that asthma, a disease of the lower respiratory system, and allergic rhinitis, an upper airway syndrome, are aspects of a single clinical condition. Labeled by one expert as "allergic rhinobronchitis," the asthma-allergy linkage includes nasal and bronchial hyperresponsiveness and inflammation in both the upper and lower airways.  For example, eosinophil recruitment seems to be part of the inflammatory cascade in both the upper and lower airways, and eosinophils are responsible for tissue damage in both the nose and the lungs. The pathogenic processes of both diseases, moreover, involve the respiratory epithelial cells, Langerhans' cells, dendritic cells, and other antigen-presenting cells; the recruitment and activation of CD4+ helper cells with the [T.sub.H]2-type phenotype; and the effector cells such as eosinophils, mast cells, and basophils. 
A close relationship
The key clinical points are that asthma and allergy may well be associated (the incidence of allergic rhinitis in adults with asthma has been estimated to be nearly 60%) ; that either condition may predetermine or exacerbate the other; and that treating the conditions concomitantly may benefit not only the primary target but also the associated condition. Until now asthma and allergic rhinitis have been considered separate conditions to be treated independently. In fact, antihistamines were often considered contraindicated in patients with both conditions. Recent data, however, not only suggest that antihistamines may have a bronchodilatory effect beneficial in asthma but that failure to treat asthma and allergy concomitantly may compromise efforts to treat either condition separately  Other studies suggest that increased incidences of asthma are correlated with an increased incidence of allergic rhinitis and that allergen exposure may be a risk factor for the eventual onset of asthma. Patients presenti ng with allergic rhinitis--especially if the symptoms are severe and if the condition is perennial--may be at risk for asthma or may already be experiencing asthmatic symptoms. Treating the allergic rhinitis promptly and efficaciously is important, as is screening for underlying evidence of asthma.
Not all asthma has an allergic component, and certainly not all allergic rhinitis is associated with asthma. Nor is wheezing, sneezing, or shortness of breath an infallible sign of asthma and allergic rhinitis. The clinician needs to determine whether one or both conditions are actually present. Paradoxically, the apparent increase in the prevalence of asthma and the increased awareness of the condition among patients may in fact increase the likelihood of misdiagnosis. A patient presents with a symptom that he believes is asthma- or allergy-related; the physician agrees and prescribes a course of pharmacotherapy. Misdiagnosis often leads to poor therapeutic response, which leads to the substitution of other and, often, more potent pharmaceuticals. Because there are now so many pharmacotherapies for the two conditions, this process may last weeks...
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