The role of sinus disease in asthma.
Some time ago, a link between upper and lower respiratory disease was described, which gave rise to the concept of 'united airways disease'. This concept primarily refers to the well established link between allergic rhinitis and asthma, but it also covers a possible link between sinus disease and asthma (allergic or nonallergic) and other lower airway disease. The current classification of chronic rhinosinusitis (CRS) includes disease without and with nasal polyps, which are considered subgroups of CRS. Different patterns of inflammatory and regulatory cytokines (involving distinguishable T-helper lymphocyte populations) and of remodelling markers, however, were recently described to differentiate nasal polyposis from CRS, yielding two discrete entities. These patterns resemble those of lower airway diseases, such as asthma and chronic obstructive pulmonary disease, and suggest a common aetiological/pathogenetic background. Whereas the link between nasal polyps and asthma is well established (indeed, asthma improves after medical or surgical treatment of sinus disease), that between CRS and lower airway disease is not well understood. Recently, Staphylococcus aureus enterotoxins, acting as superantigens, were identified as a possible link between nasal polyps and asthma, resulting in severe disease manifestations in both upper and lower airways. The role played by sinus disease in asthma is only partially understood, largely because of deficits in the clinical classification and in basic knowledge of pathophysiological pathways. Recent research into upper airway and sinus inflammation and remodelling may reveal new perspectives and lead to a classification of sinus disease, which will facilitate appropriate clinical and epidemiological studies.