Persistent cough: differential diagnosis.

Cough may be defined as a physiologic response to foreign or noxious substances that enter or irritate the respiratory tract. It is the fifth most common symptom complex for which patients seek medical care and which results in more than 30 million office visits per year. When cough is present for more than three weeks it is referred to as chronic or persistent cough. This presentation will examine the differential diagnosis of persistent cough together with a description of the autonomic innervation of the human airways, mechanism(s) of cough, and approach to the patient.