Is rhinosinusitis a cause of asthma?

There is a great deal of evidence of an association between rhinosinusitis and asthma. However, it is less clear whether rhinosinusitis is a direct trigger for asthma or the two conditions are simply manifestations of a common underlying process. Evidence for a role for rhinosinusitis as a trigger for asthma includes many examples of improvement in asthma once concomitant rhinosinusitis is treated medically or surgically. Possible mechanisms for this relationship include naso-pharyngo-bronchial reflexes, postnasal drip, abnormal breathing, and the local production of inflammatory mediators that trigger pulmonary inflammation via the bone marrow. On the other hand, evidence exists that rhinosinusitis and asthma are manifestations of a common process. For example, there are similarities between the histopathological changes in the epithelium in chronic rhinosinusitis and asthma. The bone marrow may provide the link between the upper and lower airways in creating a common disease. A second possible mechanism for a common disease is response to staphylococcal enterotoxins. Although evidence exists to suggest that rhinosinusitis either triggers asthma or represents a local manifestation of a shared disorder, the key to reconciling this apparent controversy is to consider that rhinosinusitis is not just a single, uniform disease. Current evidence suggests that rhinosinusitis with neither polyps nor eosinophilic inflammation acts as a direct trigger for asthma, whereas rhinosinusitis with both polyps and eosinophilic inflammation shares underlying mechanisms with asthma. Clearly, however, there is considerable overlap between the different, complex mechanisms that link rhinosinusitis to asthma.