What Can Be Learned From a Cough?

Nicholas Gross, MD, PhD


August 31, 2016

Types of Cough and the Information They Provide

Chronic cough is one of the most common symptoms in medicine and is said to occur in 12% of the adult population.[1] Cough is such an obvious and easily observed mechanism to clear the lungs' airways that it tends to be ignored or taken for granted. In an age of high-tech investigations, we tend to overlook the facts that not all coughs are alike and that features of a cough can be distinguished with current technology. But distinct varieties of cough can provide clues to underlying diagnoses.

Chronic cough, which is particularly troublesome to both the patient and the healthcare provider, has been investigated in a recent study.[2] Cough was induced in healthy smokers; in people with chronic obstructive pulmonary disease (COPD), asthma, or chronic cough; and in a control group of healthy patients using—in random order—inhaled airway stimulants, such as capsaicin, prostaglandin E2 (PGE2), bradykinin, and citric acid in increasing concentrations. The investigators recorded the number and frequency of coughs several minutes after inhalations. They also made acoustic recordings of coughs over the subsequent 24 hours. When challenged with capsaicin, cough was significantly more frequent in patients with COPD or asthma than in healthy nonsmokers and, most of all, in patients with undiagnosed "chronic cough." However, when challenged with PGE2, cough responses were less pronounced in patients with COPD. The investigators concluded that patients with COPD exhibit specific patterns of cough response that differ significantly not only from healthy control subjects, but also from patients with asthma or chronic cough. This study shows for the first time that people with different airway diseases exhibit different patterns of sensitivity to a range of irritant stimuli, a phenomenon the investigators call "neurophenotypes."


A shortcoming of this study is that the mechanism or mechanisms of any cough type are not addressed. It is hoped that these findings will lead to the search for biochemical and physiological abnormalities that can be corrected, relieving the distress of a common condition.

Cough serves to clear the airways. In response to upper airway infection, cough typically continues for no longer than 3 weeks, and often does not require any intervention.[3] Cough that lasts longer than that usually warrants a call or visit to a healthcare professional. Cough lasting longer than 8 weeks can be called "chronic" and deserves a work-up. Among the pulmonary causes of chronic cough are asthma, eosinophilic bronchitis, gastroesophageal reflux, sinusitis, COPD, and bronchitis. But despite clinical interventions, almost half of the people who suffer from chronic cough receive no diagnosis,[4] and the great majority receive no relief from any therapy. Identifying the different types of chronic cough could lead to more precise diagnoses, but more investigation is needed. This study is a start. By showing that there are different types of cough, we are confronted with the task of identifying cough types, "neurophenotypes," and appropriate treatments.


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