According to guidelines from the Thoracic Society of Australia and New Zealand and the American College of Chest Physicians, cough is considered chronic in children if it lasts longer than 4 weeks1,2; in guidelines from the British Thoracic Society, cough is considered chronic if it lasts 8 weeks.3 In adults, cough that lasts longer than 8 weeks is considered chronic. The pediatric guidelines are based on the natural history of acute upper respiratory tract infections. Usually, 50% of children with cough related to acute viral illness recover by 10 days, 75% recover by 16 days, and 90% recover by 25 days.4
Chronic cough in children presents some unique challenges. Many adult diagnoses, such as chronic obstructive pulmonary disease and chronic bronchitis, are not recognized entities in the pediatric literature; therefore, the underlying diagnosis may be difficult to determine. Because of the distressing nature of the symptom, it may cause anxiety among family members.
Understandably, long-standing cough is stressful for the family and patient.5 Families may seek multiple medical consultations in quest of symptom resolution. In a study of 190 children, in a 12-month period, more than 80% had more than 5 doctor visits and more than 50% had more than 10 doctor visits for chronic cough.5 Clinical studies found 2 major fears expressed by mothers were that their child was going to die as a result of choking on phlegm or vomit or of an asthma attack or cot death and that their child would have long-term chest damage as a result of ongoing cough. Mothers reported disturbed sleep because of their fears.6
PATHOPHYSIOLOGY
Cough is a protective reflex and a component of normal respiratory physiology. It enhances clearance of debris from the airway. The cough receptors are located from the larynx to the segmental bronchi. The afferent input is through the vagus nerve, and control occurs in the brainstem with cortical modulation. The efferent activity influences respiratory muscles. Cough reflex sensitivity (CRS) is affected by disease states and medications. Heightened CRS occurs with viral respiratory tract infections, asthma, gastroesophageal reflux disease (GERD), and angiotensin-converting enzyme inhibitor therapy. Children with neuromuscular weakness, chest wall deformities, tracheobronchomalacia, tracheostomies, and laryngeal dysfunction may not have an effective cough reflex. These children are at risk for aspiration, atelectasis, recurrent pneumonia, and chronic lung disease.
EPIDEMIOLOGY
The prevalence of chronic cough is reported to be 5% to 7% in preschoolers and 12% to 15% in older children.7 Cough can be classified as normal, or expected; chronic specific; or chronic nonspecific.
Normal, or expected, cough. This refers to cough in the absence of any disease states and likely represents the normal protective reflex phenomenon. In a study of healthy children with a mean age of 10 years, there was a mean frequency of 11.3 (range, 1 to 34) cough episodes per 24 hours.8 This was unaffected by passive smoking or the presence of furry pets in the home. However, nocturnal and prolonged coughing was unusual in these children.8 In older children, psychological stressors may cause cough.9,10
Chronic specific cough. This type of cough is associated with other signs and symptoms suggestive of an underlying problem.
Chronic nonspecific cough. This type is characterized by dry cough in the absence of any identifiable respiratory disease. There are greater diagnostic and management challenges with this type of cough.
Diagnoses to be considered in children with chronic cough
ETIOLOGY
The etiology of chronic cough depends on the age at onset. In a study of 108 pediatric patients with chronic cough (median age, 2.6 years), a final primary diagnosis was reached in 90%.11 The most common primary diagnosis was persistent bacterial bronchitis (39.8%). Natural resolution occurred in 22% of the patients. Asthma, GERD, and upper airway cough syndrome (UACS), common causes of chronic cough in adults, were found in only 9% of the patients. A secondary diagnosis of tracheomalacia, GERD, or obstructive sleep apnea was found 33%, 15%, and 2% of the patients, respectively.
In another study, the causes of cough in older children (mean age, 9.2 years) were found to be similar to those in adults (ie, UACS in 23%, GERD in 28%, asthma in 13%, and other diagnoses in 20%).12
Cough has been associated with environmental factors, such as outdoor and indoor air pollution. Particulate matter, irritant gases, tobacco smoke exposure, and dampness in the home have been implicated.13 The differential diagnosis of chronic cough in children is presented in Table 1.
