 Introduction/Background Chronic cough is defined by a duration lasting at least 8 weeks [1], often contributing to patient discomfort and altered psychosocial well-being [2]. The most common causes of chronic cough include smoking-related lung disease, upper airway cough syndrome (UACS), asthma, gastroesophageal reflux disease (GERD), and nonasthmatic eosinophilic bronchitis [1-3]. Cough can further be characterized by quality, that is productive or nonproductive. Conditions that may be associated with productive cough include bronchiectasis, chronic bronchitis, asthma, and immunodeficiencies [4-6]. There is varied opinion in the literature regarding the utility of cough productivity in the phenotypic stratification of chronic cough patients [5,7,8]. Cough is a protective reflex mediated by a complex network of afferent and efferent neuronal pathways [9]. Stimuli for cough can occur in the chest wall, airways, esophagus, larynx, and middle ear [10]. It is believed that a significant number of individuals with chronic cough may be suffering from cough hypersensitivity [11,12], in which the threshold for cough is lowered by repeated exposure to stimulus or inflammation [11-13]. There may be similarity in the neuronal hyperstimulation seen in chronic cough with that of chronic pain [14]. The etiology of chronic cough in some patients may be difficult to localize to an isolated source and is often multifactorial [15]. The complex pathophysiology, clinical presentation, and variable manifestations of chronic cough underscore the challenges faced by clinicians in the evaluation and management of these patients. Varying guidelines and algorithms exist for the evaluation and management of chronic cough, driven by a thorough history and physical examination, empiric treatment, and often diagnosis by exclusion [1,15,16]. Standardized clinical algorithms have shown efficacy in the diagnosis and treatment of chronic cough [7,10,16,17].
Chronic Cough.  Introduction/Background Chronic cough is defined by a duration lasting at least 8 weeks [1], often contributing to patient discomfort and altered psychosocial well-being [2]. The most common causes of chronic cough include smoking-related lung disease, upper airway cough syndrome (UACS), asthma, gastroesophageal reflux disease (GERD), and nonasthmatic eosinophilic bronchitis [1-3]. Cough can further be characterized by quality, that is productive or nonproductive. Conditions that may be associated with productive cough include bronchiectasis, chronic bronchitis, asthma, and immunodeficiencies [4-6]. There is varied opinion in the literature regarding the utility of cough productivity in the phenotypic stratification of chronic cough patients [5,7,8]. Cough is a protective reflex mediated by a complex network of afferent and efferent neuronal pathways [9]. Stimuli for cough can occur in the chest wall, airways, esophagus, larynx, and middle ear [10]. It is believed that a significant number of individuals with chronic cough may be suffering from cough hypersensitivity [11,12], in which the threshold for cough is lowered by repeated exposure to stimulus or inflammation [11-13]. There may be similarity in the neuronal hyperstimulation seen in chronic cough with that of chronic pain [14]. The etiology of chronic cough in some patients may be difficult to localize to an isolated source and is often multifactorial [15]. The complex pathophysiology, clinical presentation, and variable manifestations of chronic cough underscore the challenges faced by clinicians in the evaluation and management of these patients. Varying guidelines and algorithms exist for the evaluation and management of chronic cough, driven by a thorough history and physical examination, empiric treatment, and often diagnosis by exclusion [1,15,16]. Standardized clinical algorithms have shown efficacy in the diagnosis and treatment of chronic cough [7,10,16,17].