CHAPTER 97

Cough

Nasser Redjal, MD, and Charles H. Song, MD

Cough is an essential protective reflex that allows for clearance of secretions and particulates from the airways. Its persistence can be distressing to the pediatric patient and often causes parental anxiety because of uncertainty of its etiology. Cough may be acute, subacute, or chronic. Acute cough lasts less than 2 weeks and often is associated with respiratory tract infections in children. Cough lasting 2 to 4 weeks is subacute, and cough lasting more than 4 weeks is persistent or chronic. In children 15 years and older as well as adults, chronic cough usually is defined as persistent cough lasting more than 8 weeks. Parental awareness as well as accessibility to medical care influences the timing of the initial visit to a physician or other health professional during the disease course. Cough may be classified as specific or nonspecific depending on whether an underlying etiology is found, and management of the disease is tailored accordingly.

Epidemiology

Cough is a common reason for pediatric office visits. In the National Ambulatory Medical Care Survey, 6.7% of pediatric office visits involved children who presented with cough. Typically, preschool age children have up to 8 upper respiratory infections with associated cough in a winter season. Persistent cough is also common, with some surveys demonstrating a prevalence of 5% to 10% in 6- to 12-year-old children, with higher rates in younger children. Cough is more common among boys than girls less than 11 years of age and may be less common in developing countries than affluent countries.

Clinical Presentation

Presentation varies considerably depending on the etiology of the cough. Most children have no evidence of respiratory compromise, but some present with respiratory distress. Depending on the underlying etiology, a child may manifest other symptoms of chronic lung disease, such as clubbing and failure to thrive, although most children are found to be in good health.

Pathophysiology

Coughing is a protective reflex that is automatically triggered by cough receptors found throughout the human airway, including the nose, paranasal sinuses, posterior pharynx, larynx, trachea, bronchi, and pleura. They are also found outside the respiratory tract in the ear canal, stomach, pericardium, and diaphragm (Figure 97.1).

Proximal airways (ie, larynx and trachea) are more sensitive to mechanical stimulation, and distal airways are more sensitive to chemical stimulation. Lung parenchymal (ie, bronchiolar and alveolar) tissue contains no cough receptors; thus, pneumonia may not produce a cough. Stimulation of any of these receptors by an irritant, whether mechanical, chemical, thermal, or inflammatory, can initiate the cough reflex. Impulses from stimulated cough receptors traverse afferent nerves (ie, vagus, glossopharyngeal, trigeminal, phrenic) to a “cough center” in the medulla, which itself is under some control by higher cortical centers. The cough center generates an efferent signal that travels down the vagus, phrenic, and spinal motor nerves to expiratory musculature, thereby producing the cough. The cough center can be voluntarily stimulated or suppressed. Once initiated, the cough reflex propels excess mucus up the airways at the pressures of up to 300 mm Hg and at flows of up to 5 to 6 L/sec.

Figure 97.1. The cough reflex.

The cough experienced by patients may be broken down into 4 phases. First, the glottis opens with an inspiratory gasp. Second, the glottis closes with forceful contraction of the chest wall, diaphragm, and abdominal muscles. Third, the glottis again opens with release of airway pressure in an expiratory phase. Fourth, the chest wall and abdominal muscles relax. This process expels mucus or irritants from the airways, helping maintain lung health. The child who does not cough effectively may be at risk for atelectasis, recurrent pneumonia, and chronic airway disease from aspiration or retention of secretions.

Differential Diagnosis

Any pathology present along the airway from the nose to the alveoli can elicit a cough response; therefore, the list of differential diagnoses of cough is long (Box 97.1). Narrowing the list of causes can be accomplished by paying attention to several factors (Box 97.2). Typically, wet (ie, productive) cough tends to point to more specific diagnosis, whereas dry cough may be nonspecific.

The age of the child is an important determinant in the differential diagnosis. Cough presenting during infancy should prompt the physician to consider congenital chest anomalies, such as tracheoesophageal fistula, laryngeal cleft, vocal cord paralysis, and tracheobronchomalacia. Other congenital conditions include heart disease, which can produce a cough as the result of heart failure and pulmonary edema. Congenital mediastinal tumors induce cough if the tumor presses on the airway. Recurrent coughing or wheezing in infancy and early childhood associated with respiratory syncytial virus infection may be early signs of impending asthma in later childhood. Recurrent vomiting during infancy associated with chronic cough is suspicious for gastroesophageal reflux disease (GERD).

The duration of the cough is an important factor in determining the possible etiology. Most acute coughs are caused by a viral respiratory infection. The common viruses involved are rhinovirus, respiratory syncytial virus, human metapneumovirus, and adenovirus in infants and younger children; influenza and parainfluenza are common in children of all ages. All of these viruses affect the upper respiratory tract (common cold) more commonly, usually peaking on day 2 to 3 of illness and resolving in 2 weeks. Other causes of acute cough include asthma, bacterial upper respiratory infection (eg, pharyngitis, sinusitis), and pneumonia. The most commonly involved bacteria are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.

In some children, especially those with underlying allergy or mild immune deficiency, cough may persist beyond 2 weeks after initial common cold symptoms appear. Virus may spread to the sinuses (ie, acute sinusitis) or to the lungs as pneumonia, bronchitis, or bronchiolitis. A secondary bacterial infection may also involve the sinuses and the lungs.

Cough lasting longer than 4 weeks is defined as chronic, and causes other than those associated with acute cough must be considered. In adolescents 15 years and older and adults, asthma, upper airway cough syndrome (eg, postnasal drip resulting from rhinitis or sinusitis), and GERD are the most common etiologies.

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