In the United States, cough is the most common complaint for which patients seek medical attention and is the second most common reason for a general medical examination, accounting for more than 26 million office visits annually. Cough often results from an acute, self-limited, viral upper respiratory tract infection; however, there are multiple causes of cough beyond this, including both respiratory tract and nonrespiratory tract-related etiologies. Cough that lasts more than 4 weeks in children younger than 14 years of age or more than 8 weeks in adolescents and adults 14 years of age and older is considered to be chronic by the American College of Chest Physicians (ACCP). Cough serves a potentially beneficial purpose by clearing the airways of excessive mucus, irritants, or abnormal substances such as edema fluid or pus. But while cough may serve a useful function, it can also lead to a variety of problems, including exhaustion (57%), feeling self-conscious (55%), insomnia (45%), changes in lifestyle (45%), musculoskeletal pain (45%), hoarseness (43%), excessive perspiration (42%), and urinary incontinence (39%). These problems are more likely to be prominent in the setting of chronic versus acute cough. As a consequence, chronic cough is responsible for up to 38 percent of pulmonary outpatient visits. To effectively assess cough and monitor response to treatment, it is essential to have valid measurement tools. Currently there are many different tools used to assess cough frequency and severity, including quality-of-life questionnaires, visual analog scales, electronic recordings, and human counts. It is important to determine whether the tools currently in use accurately assess cough and response to treatment. While no universally accepted gold standard exists for comparison, data regarding the validity, consistency, reliability, and responsiveness of these tools are needed. The purpose of this review is to evaluate the effectiveness of instruments to evaluate cough and the comparative effectiveness of treatments for the symptom of cough in patients with either unexplained or refractory chronic cough. In patients with no identifiable cause of cough (unexplained or idiopathic) or no response to specific treatment (unresponsive, refractory, or intractable), chronic cough poses a particularly challenging problem. The differential diagnosis for chronic cough has a different list of etiologies compared with acute cough. Treatment for chronic cough contrasts with acute cough in that acute cough treatment may focus on curing the underlying etiology (e.g., bacterial bronchitis or pneumonia) or suppressing symptoms for the short period of time needed for the etiology to resolve spontaneously (e.g., viral etiologies). Cough becomes chronic if it persists, often due to an underlying etiology that is difficult to diagnose or treat. Therefore, treatments for cough may have differential effectiveness depending on whether the cough is acute versus chronic. Side effects of medication may also become more salient in the setting of chronic cough given that treatment duration is longer, allowing more opportunity for side effects to occur. Chronic cough also differs from acute cough in that quality of life may be affected more severely and in different ways than with acute cough. Recent studies from the United Kingdom, United States, and Japan evaluating patients with chronic cough have estimated that up to 46 percent of patients have idiopathic cough despite a thorough diagnostic investigation.
