Epidemiological evidence suggests that asthma and rhinitis frequently occur as co-morbid conditions in the same patients, with about 80-90% of asthmatic patients having rhinitis symptoms and about 20-50% of patients with allergic rhinitis (AR) having clinical asthma. Furthermore, rhinitis often precedes the onset of clinical asthma and independently increases the risk for developing asthma by up to 3-fold. There is increasing evidence that AR and asthma are linked and may therefore be manifestations of the same airway disease, rather than two distinct diseases of the nose and the lung. Similarly, some studies have demonstrated that treatment of either condition in co-morbid disease may result in improvement of the other. Although several mechanisms have been proposed to explain the pathophysiological link between the upper and the lower airways, the precise mechanisms underlying the link between AR and asthma are not clearly understood. Natural and experimental allergen provocation indicates that inflammation of the nasal and bronchial mucosa is important, because it is triggered by factors common to both mucosae and plays a pivotal role in the pathogenesis of both AR and asthma. More recent data suggest that bidirectional systemic inflammation involving the bone marrow is also likely to be important, since allergen provocation leads to up-regulation and release from the bone marrow of haemopoietic eosinophil/basophil progenitor cells, which migrate to the tissues and undergo differentiation and activation in situ. Studies of intranasally applied corticosteroids and antihistamines (particularly cetirizine) have shown beneficial effects in both the upper and lower airways of patients with seasonal AR, and provide additional indirect support for this mechanism.

Airway inflammation, Allergen provocation, Co-morbid asthma and allergic rhinitis, Eosinophilia, Systemic disease
dx.doi.org/10.1111/j.1365-2222.2005.0077.x, hdl.handle.net/1765/63362
Clinical and Experimental Allergy Reviews
Department of Pulmonology

Fokkens, W.J, & Braunstahl, G.J. (2005). One airway, one disease?. Clinical and Experimental Allergy Reviews (Vol. 5, pp. 16–20). doi:10.1111/j.1365-2222.2005.0077.x