A thorough differential diagnosis, primarily based on history and physical examination, is essential when a child presents with a suspicious cough. Certain imaging modalities are also useful for diagnosis.
Identification of an underlying cause is crucial. When doing your history and physical exam, look for something that does not fit a routine presentation. For example, a cough in the presence of a constitutional change, such as weight loss, can indicate a more serious problem. In addition, a cough with a relatively sudden onset or one associated with labored breathing can be worrisome. Also, a choking episode followed by sudden cough, for example, can indicate the presence of a foreign body.
Asthma is the most common cause of chronic cough in the pediatric population, but also consider less common etiologies such as tracheoesophageal fistula, cystic fibrosis (CF), and bronchopulmonary dysplasia. Failure to thrive, clubbing, cardiac signs, and persistent stridor suggest alternative diagnoses.
Patient age offers some guidance in your differential diagnosis. In a neonate (younger than 28 days), persistent cough might suggest an infection or a congenital anomaly such as compression of the esophagus and trachea by a vascular ring. Infectious etiologies include rhinovirus, adenovirus, respiratory syncytial virus, and pertussis.
In preschool children, think upper or lower respiratory tract infection, rhinitis, postnasal drip syndrome, gastroesophageal reflux, an irritant source (such as passive smoking or air pollution), and, of course, asthma.
Among school-age children and adolescents, consider the same possibilities, but add inhalant or other substance abuse to your list of possible irritant causes. In addition, these older children can develop psychogenic or “habit” cough, one that is absent during sleep, distraction, or periods of concentration. Vocal cord dysfunction, also known as laryngeal wheeze, is another possibility in this group.
General pediatricians commonly treat children with a cough that lasts 5-10 days in the context of an upper respiratory tract illness, such as a cold. If a child still coughs incessantly after other cold symptoms have resolved, I would be concerned. This is not necessarily a call to refer the patient to a specialist, but this scenario is a call to do further diagnostic evaluation.
If the child already is diagnosed with asthma and develops a cough, determine whether the patient is taking the appropriate medication and/or is compliant with therapy. Also, ask about the child's environment, particularly the presence of passive smoking, dust, and pets.
In terms of allergy testing, I recommend a radioallergosorbent allergen-specific IgE antibody assay. This is indicated if a child has other lateral symptoms, such as eczema, and/or during peak times for seasonal allergies.
It is helpful when pediatricians do spirometry for a child with a suspicious cough. Nationwide, about 20%-25% of general pediatricians do pulmonary function testing. Pediatric pulmonologists like me would like to see more pediatricians perform these tests. Sinus x-rays also can be helpful, and are within the purview of the general pediatrician. Some might consider this an unnecessary test, however, or one for which you need a high index of suspicion before ordering.
A test that is generally unnecessary is a sweat test for cystic fibrosis. A lot of pediatricians get this test, and I would not tell them not to because often the child with CF has other symptoms that are more diagnostic.