INTRODUCTION

The symptom of cough, which is responsible for approximately 30 million clinician visits annually in the United States, is one of the most common symptoms for which outpatient care is sought [1]. In an outpatient pulmonary practice, evaluation and management of persistent cough can account for up to 40 percent of the practice volume [2].

Cough can be classified based upon the duration of the cough; within each category are likely diagnostic possibilities. Acute cough exists for less than three weeks and is most commonly due to an acute respiratory tract infection. Other considerations include an acute exacerbation of underlying chronic pulmonary disease, pneumonia, and pulmonary embolism.

Cough that has been present longer than three weeks is either subacute (three to eight weeks) or chronic (more than eight weeks) [1]. Patients who seek medical attention for chronic cough are more likely to be female [3-5]. Among patients with chronic cough, women tend to cough more often and to have heightened cough reflex sensitivity compared to men [4].

The common etiologies, complications, and evaluation of subacute and chronic cough will be reviewed here. The treatment of subacute and chronic cough is described separately. (See "Treatment of subacute and chronic cough in adults".)

COUGH REFLEX ARC

Each cough occurs through the stimulation of a complex reflex arc. This is initiated by the irritation of cough receptors that exist not only in the epithelium of the upper and lower respiratory tracts, but also in the pericardium, esophagus, diaphragm, and stomach. Chemical receptors sensitive to acid, cold, heat, capsaicin-like compounds, and other chemical irritants trigger the cough reflex via activation of ion channels of the transient receptor potential vanilloid type 1 (TRPV1) and transient receptor potential ankyrin type 1 (TRPA1) classes [6-10]. (See "Neuronal control of the airways", section on 'Reflex regulation'.)