Chronic cough, defined by custom as one that persists for longer than 3 weeks, often is misdiagnosed as asthma. Chronic or recurrent cough in childhood affects up to 25% of schoolchildren and accounts for 2.5% of outpatient consultations in the United States.1,2 This is in addition to the 30% of consultations for upper respiratory tract infection; many of these patients complain of cough. The most common cause for chronic or recurrent cough is viral upper respiratory tract infections3 but there is of course a wide differential diagnosis (Tables 1 and 2).
The diagnosis of asthma in a child presenting with cough without wheezing is not easy. The evidence that cough is a marker for asthma is not good, and there is concern that too many children with only cough are being labeled asthmatic and treated inappropriately.4 This article considers how the primary physician should evaluate cough and examines the relationship of cough and asthma.
EVALUATION OF CHRONIC AND RECURRENT COUGH
Recurrent viral infections and atmospheric pollutants are the main causes of chronic or recurrent cough. Clinical evaluation will identify the few children who need further investigation. The presence of the following factors provide insight into these diagnoses for infants:
* large families increase exposure to viruses,
* passive smoking increases the risk of cough,
* postbronchiolitis wheezing may be heard only at certain times of the day or when the child is crying or feeding,
* immunization status may be incomplete for pertussis,
* mild conjunctivitis following birth suggests chlamydia infection,
* vomiting and choking during feeds, especially in a handicapped infant, suggest aspiration due to reflux (and very rarely, a tracheoesophageal fistula),
Common Causes of Isolated Chronic or Recurrent Cough
Causes of Chronic Cough That Usually Present With Other Signs or Symptoms
* poor growth and diarrhea suggest cystic fibrosis, acquired immunodeficiency syndrome, or immunodeficiency, and
The following are clues to the etiology of chronic or recurrent cough in children:
* large families and nursery or school attendance increase exposure to viruses,
* a history of choking is found in 80% of those who have inhaled foreign bodies,
* the child with tuberculosis is unwell and febrile by the time he or she is coughing,
* a productive cough suggests bronchiectasis or a foreign body,
* a honking or brassy cough in an otherwise healthy child suggests tic or habit coughing,
* asthma is likely if symptoms are exercise-induced or if there are diurnal variations in PEF (in adolescents), wheezing, a positive family history for asthma, or other signs of atopy, and
* snoring, sniffing, and mouth breathing suggest ear, nose, and throat problems such as tonsil/adenoid enlargement, rhinitis, or sinusitis.
There often will be nothing abnormal to find on physical examination, but nevertheless this must be thorough as it will relieve parents and is thus of therapeutic value. The examination should include evaluation of the following:
* Growth velocity. Growth rate should be determined with the use of a growth chart; poor growth should be taken as a flag for underlying pathology,
* Chest shape. Increased chest diameter suggests hyperinflation and asthma or cystic fibrosis should be considered.
* Respiratory rate. Rapid breathing in an infant suggests underlying chest or heart disease.
* Mouth breathing. Mouth breathing suggests upper airway obstruction due, for example, to large tonsils or adenoids.
* Wheezing. Wheezing is typical of asthma and focal wheezing with crackles suggests bronchiectasis or an inhaled foreign body.
* Clubbing. If clubbing is present and you have been the primary physician, look out for litigation!
Very few children will need investigations, and these are undertaken more to exclude diagnoses than to confirm diagnoses (Table 2). The diagnosis of asthma in the young child is particularly difficult.
There is no good antitussive in children. Treatment is of the underlying condition. Figure 1 is a recommendation for information that should be posted in the primary physician's waiting room and can be supplemented with a leaflet.
CHRONIC COUGH AND ASTHMA
Asthma generally is considered a condition in which there is reversible airway obstruction. However, lack of an acceptable epidemiological definition for asthma and lack of objective measures that are both sensitive and specific hamper the formulation of a convincing link between cough without wheeze and asthma.5
Cough is a powerful physiological mechanism that protects the lung from inhaled or aspirated foreign material. It is a reflex and results from stimulation of receptors concentrated at the larynx, trachea, and bifurcation of the larger bronchi6 (Figure 2). Several mechanisms have been proposed as increasing cough reflex sensitivity7'9: viral infections strip away airway epithelium and pollutants may compound this while local mediators increase sensitivity.
Figure 1. Sample notice to post in physicians' offices.
Figure 2. Diagram of cough receptors.
The increased sensitivity in asthma is not present if the asthma is well-controlled. Good control presumably reflects modification of inflammation10 because airway caliber reflecting bronchomotor tone does not seem to cause the cough in asthma.11'13 Cough and bronchoconstriction are closely related because both can be triggered by the same things and they potentiate each other. However, each can be triggered independently.14 Thus, cough in asthma seems to be associated with the mediators associated with airway inflammation and direct sensitivity to triggers such as viral infections.
Epidemiological studies suggest that cough is a very poor marker for asthma. Major studies have established wheezing as the epidemiologic marker for asthma15,16 Adding cough without wheezing would confuse comparisons of prevalence. Clough et al17 found that 12% of schoolchildren wheeze and 25% have cough. Further, 20% of 7 year olds and 9% of 1 1 year olds have cough without wheeze. In a study of 156 children diagnosed asthma, Luyt et al18 found that only 17 had cough without wheeze. However, most convincing is that only 11% of children with cough turned out to have asthma; this is about the incidence of asthma in the general population.19
ASSESSING WHETHER COUGH IS ASTHMA
It is well recognized that parents and children may not perceive wheeze.20 Diaries and peak flow recordings might disclose this.
Diaries in the Assessment of Cough
Diaries record cough and wheeze on a severity scale during the day, at night, and on exercise. Peak flow also can be recorded if the child is able to use the meter properly. Variation in peak flow >20% during the day suggests bronchial lability. Once use of a diary with peak flow readings has been established, one can assess the response to a therapeutic trial of a drug.
Diaries and peak flow recordings do have limitations. Nighttime cough included in most diaries is poorly validated. Parents' records of cough compare poorly with voice-activated tapes.21 Even in established asthma, the significance of nighttime cough without wheeze is uncertain.22 It is also true that entries in diaries are made in batches and may not be true reflections of coughing.23 Inexperienced children can record very different peak flow measurements within the same session, and so the 15% to 20% diurnal variation found in adults with asthma may be less dependable in children.
Provocation testing with methacholine or histamine, or by exercise has been used extensively in asthma research. These tests have severe limitations in the evaluation of the individual. Significant bronchoconstriction on exercise seldom is found in nonasthmatics; however, 20% of asthmatics do not have positive exercise tests.24 In addition, nonspecific challenges are not helpful in distinguishing asthma from recurrent cough.25
ASTHMA DRUGS IN THE TREATMENT OF COUGH
There is no proof that antiasthma medication has any value in the treatment of cough without wheeze:
* inhaled beta-agonists are of no value,26
* inhaled beta-agonists also are of no value in cough associated with asthma,27
* "chronic allergic cough" can respond to terbutaline in adults but many of these patients were also wheezy,28
* neither corticosteroids29 nor theophylline have any proven value, and
* there are no randomized trials to evaluate any of the antitussives in children.
A trial of beta-agonist treatment is likely to identify a few children who might benefit from asthma treatment. However, improvement after treatment could be coincidental and represent resolution of a viral infection or placebo effect. There is also nothing to support the treatment of cough with corticosteroids. In view of side effects as well as cost, we believe this is unjustified until there is evidence of value.
WHAT SHOULD BE THE PRIMARY PHYSICIAN'S APPROACH TO THE CHILD WITH A CHRONIC COUGH?
The vast majority of children with no other physical signs will turn out healthy. Parents should be appraised of this. Conditions such as cystic fibrosis, inhaled foreign body, and other rare conditions always have other pointers to the diagnosis if you look carefully. There should be no need for an expensive work-up for the regular cougher. Parents never seem to bring coughing children to the physician when they are at their worst, so you might ask them to bring the child back when they are particularly concerned. At this time, auscultation can be carried out when the child is perceived to be "ill." it is true that asthma has in the past been underdiagnosed; we now should be careful not to overdiagnose.
It is difficult to make a diagnosis of asthma on cough alone. This diagnosis is particularly difficult in preschool children in whom wheezing can be difficult to recognize. A trial of beta-agonists for a short period can be helpful.
Although the primary physician knows that very few patients will have anything other than a self-limiting condition, he or she should have a systematic approach because parents need reassurance. Time spent explaining the problem is more logical and cheaper than hasty prescribing or referral for specialist opinion.
1. Clifford RD, Radford M, Howell JB, Holgatc ST. Prevalence of respiratory symptoms among 7 and 1 1 yeat old schoolchildren and association with asthma. Arch Dis Child. 1989;64:1118-1125.
2. McLemore T, DcLozier JE. 1985 Summary: National Ambulatory Medical Care Survey. Advance Data From Vital and Health Statistics, No 88. Hyattsville, Md: US Dept of Health and Human Services; 1987. Publication |PHS| 87-1250.
3. Reisman J), Canny GJ, Levison MD. The approach to chronic cough in childhood. Ann Allergy. 1988;61:163-169.
4. McKenzie S. Cough- but is it asthma? Arch Dis Child. 1994;70:1-2.
5. Phelan P. Asthma in children: epidemiology. BMJ. 1994;308:1584-1585.
6. Fuller RW, Jackson DM. Physiology and treatment of cough. Thorax. 1990;45:425430.
7. Empey DW, Laitinen LA, Jacobs L, Gold WM. Mechanisms of bronchial hyperreactivity in normal subjects after upper respiratory tract infection. Am Rev Respfr Dis. 1976;113:131-139.
8. Higgenbonora T. Cough induced by changes of ionic composition of airway surface liquid. Bulletin of European Wiysiopathology and Respiration. 1984;20:553-562 .
9. Chouddry NB, Fuller RW, Pride NB. Sensitivity of the human cough reflex: effect of inflammatory mediators prostaglandin E2, bradykintn and histamine. Am Rev Respfr Dis. 1989;140:137-141.
10. Fujimurap M, Sakamoto S, Kamio Y, Matsuda T Cough receptor sensitivity and bronchial responsiveness in normal and asthmatic subjects. Eur Respfr J. 1992;5:291-295.
11. Pounsford JC, Birch MJ, Saunders KB. Effect of bronchodilators on the cough response to inhaled citric acid in normal and asthmatic subjects. Thorax. 1985;40:662-667.
12. Fujimura M, Sakamoto S, Kamio Y, Matsuda T. Effects of methacholine induced bronchoconstriction and induced bronchodilatation on cough receptor sensitivity to inhaled capsaicin and tartaric acid. Thorax. 1992;48:615-618.
13. Fujimura M, Sakamoto S, Kamio Y, Bando T, Kurashima K, Matsuda T Effect of inhaled procaterol on cough receptor sensitivity to capsaicin in patients with asthma or bronchitis and in normal subjects. Thorax. 1993;48:441-445.
14. Cough and wheeze in asthma: are they interdependent.' Lancet. 1988;1:447-448.
15. Peat JK, Salome CM. Brett GT, Bauman S, Woolcock AJ. Reliability of a respiratory history questionnaire and effect of mode of administration on classification of asthma in children. Chest. 1992;102:153-157.
16. Anderson HR, Butland BK, Strachan DP. Trends in prevalence and severity of childhood asthma. Br Med J. 308:1600-1604.
17. Clough JB, Williams JD, Holgate ST. Effect of atopy on the natural history of sx, Pef, and BR in 7 and 8 year old children with cough and wheeze. Am Rev Respfr Dis. 1991;143:755-760.
18. Luyt DK, Burton PR, Simpson H. Epidemiological study of wheeze, doctor diagnosed asthma and cough in preschool children. BMJ. I993;306:l 386.
19. Galvez RA, McCloughin FJ, Levison H. The role of metacholine challenge in children with chronic cough. Allergy CIm Immunol. 1987;79:771-775.
20. Boner AL, De Sefano G, Piacentini GL, et al. Perception of bronchoconstriction in chronic asthma. J Asthma. 1992;295:323-330.
21. Atcher LNJ, Simpson H. Night cough counts and diary card scores in asthma. Arch Dis Child. 1985;60:473-474.
22. Hill RA, Standen PJ, Tattersfield AE. Asthma, wheezing and absence in primary schiwls. Arch Dis Child. 1989;64:246-251.
23. Hyland ME, Kenyon CAO, Allen R, et al. Diary keeping in asthma: comparison of written and electronic methods. BMJ. 1993;106:453-456.
24. Anderson SD, Silverman M, König P, Godfrey S. Exercise induced asthma. British Journal of Diseases of the Chest. 1975;69:1-39.
25. Sears MR, Jones DT, HoUaway MD, et al. Prevalence of bronchial reactivity to inhaled methacholine in NZ children. Thorax. 1986;41:283-289.
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28. Ellul-Micallef R. Effect of terbutaline sulphate on chronic allergic cough. Br Med J. 1983;287:940-943.
29. Evald T, Munch EP, Kok Jensen A. Chronic non asthmatic cough is not affected by inhaled heclomethasone dipropnonate. Allergy· 1989;44:510-514.
Common Causes of Isolated Chronic or Recurrent Cough
Causes of Chronic Cough That Usually Present With Other Signs or Symptoms