Symptom research on chronic cough: a historical perspective.

This review provides a perspective on how research on the management of cough has evolved, looks at key methodologic lessons that have been learned from this research and how they may relate to the management of other symptoms, identifies important methodologic challenges that remain to be solved, and lists important questions that still need to be answered. Three important methodologic lessons have been learned. First, cough must be evaluated systematically and according to a neuroanatomic framework. Second, the response to specific therapy must be noted to determine the cause or causes of cough and to characterize the strengths and limitations of diagnostic testing. Third, multiple conditions can simultaneously cause cough. Among the three methodologic challenges that still need to be solved are 1) definitively determining the diagnostic accuracy and reliability of 24-hour esophageal pH monitoring and how best to interpret pH test results, 2) definitively determining the role of nonacid reflux in cough due to gastroesophageal reflux disease, and 3) developing reliable and reproducible subjective and objective methods with which to assess the efficacy of cough therapy. Numerous important clinical questions are still unanswered: What role do empirical therapeutic trials play in diagnosing the cause of chronic cough? What is the most cost-effective approach to the diagnosis and treatment of chronic cough: empirical therapeutic trials or laboratory testing-directed therapeutic trials? How often is environmental air pollution, unrelated to allergies or smoking, responsible for chronic cough?