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Upper airway cough syndrome — Several studies suggest that upper airway cough syndrome related to postnasal drip is a common cause of subacute and chronic cough [2,11,12,16] . Underlying reasons for postnasal drip include allergic, perennial nonallergic, and vasomotor rhinitis; acute nasopharyngitis; and sinusitis [17] . Once secretions are present in the upper airway, cough is probably induced by stimulation of cough receptors within the laryngeal mucosa.
Symptoms of postnasal drip include frequent nasal discharge, a sensation of liquid dripping into the back of the throat, and frequent throat clearing [2] . However, postnasal drip may also be "silent," so that the absence of these symptoms does not necessarily exclude the diagnosis [12] . Clues on physical examination are a cobblestone appearance to the nasopharyngeal mucosa and the presence of secretions in the nasopharynx.
Because the symptoms and signs of postnasal drip are nonspecific, there are no definitive criteria for its diagnosis, and it is ultimately the response to therapy that secures the diagnosis. When an alternative specific cause for cough is not apparent, empiric therapy of postnasal drip should be attempted before embarking on an extensive diagnostic work-up for other etiologies [1] .
There is a strong statistical association between allergic rhinitis and asthma. Twenty-eight to 50 percent of patients with asthma appear to have allergic rhinitis
At least four mechanisms have been proposed to explain this possible connection [34] : Nasal inflammation may contribute to bronchospasm via the nasobronchial reflex. The increased expression of intracellular adhesion molecules (such as ICAM-1) associated with nasal inflammation could increase the frequency of viral infections including rhinovirus, which binds directly to ICAM-1. Inflammatory nasal cytokines from the nose could be aspirated into the lower airway inducing bronchial inflammation. Nasal inflammation could contribute to T-cell homing to the lower respiratory tract where these lymphocytes foster inflammation.
The persistent inhalation of cold dry air because of mouth breathing may also contribute to the association.
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