Chronic cough in children

Summary

Chronic cough has been variably defined as a cough lasting longer than 3, 4 or 8 weeks. Many post viral or pertussis like illnesses are associated with prolonged coughing that resolves over time. Management involves first trying to make a diagnosis and identify the presence of any underlying condition. Targeted treatments can then be employed. Trials of treatments are often used to make a diagnosis. Because natural resolution of cough is so common any trial of treatment to confirm a diagnosis should be time limited and the treatment only restarted if the coughing returns. Only a small proportion of children with an isolated non-specific dry cough have asthma and care is needed not to over diagnose asthma. Children with chronic wet cough may have protracted bacterial bronchitis (PBB) that responds to a full course of antibiotics. Children with PBB failing to respond to treatment or with specific pointers should be investigated for specific causes of suppurative lung disease.

Introduction

Chronic cough is one of the most common symptoms that parents will present with their children to the physician. Coughing is often distressing and impacts on the child's ability to sleep well, play and attend school. There is often a discrepancy between what parents and paediatricians consider to be normal. In addition, the reporting of cough is not always accurate and may depend on how parents or school teachers are affected by the child's coughing. The underlying diagnosis in chronic cough can remain elusive and for many there are no specific or effective treatments available. It is therefore often a frustrating consultation for both paediatricians and parents. Most respiratory disorders can present with coughing and the list of causes of chronic cough is large. Several national and international guidelines on the management of cough in children have been published.1, 2

Cough is one of the most important airway protective reflexes which is under both voluntary and involuntary control. Cough receptors which sense and respond to changes in temperature, chemicals and mechanical stresses are located in the pharynx, larynx and tracheobronchial tree. When stimulated these receptors send signals back to the cough centre in the medulla oblongata which then triggers the easily recognizable sequence of events that constitute a cough. A deep inspiration precedes closure of the glottis with a subsequent forceful contraction of the respiratory muscles, the glottis then opens, and there is a forceful expulsion of air, mucous and potentially any other foreign body. During the initial deep inspiration children can inhale any foodstuff that is in the pharynx or larynx exacerbating any choking or coughing. The mechanism of the cough obviously depends on intact receptors, nerves, a functioning cough centre and sufficiently strong expiratory and laryngeal muscles. The cough reflex is lost when consciousness in significantly impaired. Centrally acting cough suppressants are therefore ineffectual because of the degree of sedation required to produce cough suppression.

Normal children cough on average 11 times per day when they are well with the coughing increasing in frequency and severity during the frequent winter URTIs.³

In general there are a few overlapping reasons underlying why children appear to have problem chronic cough:

• they are repetitively trying to prevent pulmonary aspiration

• they have chronic airways irritation and inflammation

• they have chronic airways mucus hypersecretion

• they have some extra respiratory cause of the cough

Given that coughing is an important protective reflex it isn’t logical to try to suppress coughing without first identifying and treating the underlying reason.

One in ten otherwise normal children with acute cough due to an upper respiratory tract infection (URTI) are still coughing 3 weeks later.⁴ Many of these children have what has been labeled a ‘post infectious cough’ (prolonged acute coughing after an obvious URTI) perhaps due to a pertussis, mycoplasma or other viral infection.5, 6 Some children have a tendency to develop cough receptor hypersensitivity (CRH) following each viral URTI (recurrent prolonged acute coughing) and this state of CRH can last many weeks to months (Figure 1).7, 8

Defining chronic cough as lasting longer than 8 weeks is therefore preferable to using a shorter duration e.g. 3–4 weeks. Eight weeks was used in the British Thoracic Society Guideline Recommendations for the assessment and management of cough in children (1). Providing that the child is otherwise well, waiting for and checking that natural resolution has occurred is reasonable. However this duration of a chronic cough is defined largely on the basis of epidemiology rather than pathology. A cough of shorter duration can be highly significant in neonates or in older children with other ‘red flag’ symptoms. A wait and see policy should not be undertaken if ‘red flag’ alerts are present (Box 1).

It is unclear whether children with frequently recurrent cough in the absence of URTI should be assessed and managed any differently from children with true chronic coughing. Brooke et al.⁹ investigated the long term outcome of 125 pre-school children with recurrent cough. Over time more than 50% had outgrown the coughing, but only 10% had started to wheeze. The remainder of children who continued to have recurrent cough showed an increased prevalence of nocturnal coughing and decreased threshold to inhaled methacholine. Interestingly, nearly 17% of the control children were nocturnal coughers.⁹