Table 1.
Comorbid conditions associated with chronic cough in patients with IPF.
| System | Diagnosis | Proposed mechanisms of cough | Prevalence in IPF |
|---|---|---|---|
| Respiratory and sleep | Infection: tuberculosis, pertussis, lung abscess, protracted bacterial bronchitis | Excess mucous production, loss of ciliary structure, airway inflammation | NA* |
| Chronic obstructive pulmonary disease, bronchiectasis | Excess mucous production, C-fiber nerve activity | 6–67% (37) | |
| Asthma | Bronchial hyperreactivity | 8.5–18.6% (38)† | |
| Lung cancer | C-fiber nerve activity | 10–30% (39) | |
| Obstructive sleep apnoea | Upper airway inflammation and injury due to airway obstruction | 22–90% (40) | |
| Ear nose and throat | Earwax or foreign body | Stimulation of branch of the vagal nerve innervating external auditory canal | NA |
| Chronic sinusitis | Direct irritation of the vocal cords, sensitization of the cough reflex | NA | |
| Vocal cord dysfunction | Paradoxical vocal cord movement and glottis closure with airway narrowing | NA | |
| Gastrointestinal | Gastro-esophageal reflux disease | Microaspiration and direct irritation, sensitization of the cough reflex due to activation of vagal nerve endings in the esophagus | 87–94% (41–44)‡ |
| Cardiovascular | Left ventricular failure | Pulmonary c-fibers activated by pulmonary venous congestion and oedema (45) | 4–26% (37) |
| Arrhythmia | Mediators of cough (bradykinin and substance P) accumulate in the upper airway | NA§ | |
| Drugs/toxins | Angiotensin-converting enzyme inhibitor use | Mediators of cough (bradykinin and substance P) accumulate in the upper airway | NA¶ |
IPF, idiopathic pulmonary fibrosis; NA, not available; TB, tuberculosis.
*
Incidence of TB 6.3% (46) in an observational study of 143 patients in South Korea.
†
Asthma diagnosed in the year prior to IPF diagnosis.
‡
GOR measured by ambulatory pH monitoring rather than impedance.
§
In a retrospective study of patients who underwent lung transplantation for IPF, the incidence of atrial arrhythmia was 25.4% in 366 patients (47).