Update on childhood asthma

Asthma is a chronic inflammatory condition of the lower airways. It leads to breathing difficulties due to narrowing of the bronchial tubes. It is common in childhood but may occur throughout life, even presenting for the first time with symptoms in the elderly. Many hypotheses have been proposed to explain asthma,¹ however to date, the aetiology remains uncertain. Eighty per cent of children with asthma are atopic and approximately 80% of those will react to house dust mite. Of children with asthma, 50% may have concurrent allergic rhinitis (AR).

The respiratory tract actually begins at the nose, which warms and humidifies inhaled air in preparation for its passage down through the larynx and trachea. In cross section, the bronchial tubes consist of the mucosa, which is in direct contact with the inhaled air, and a smooth muscle layer, which surrounds the lining layer. In asthma, the mucosa becomes inflamed, the lining becomes swollen, the local small blood vessels become engorged, and an excess of mucus is produced. The surrounding smooth muscle becomes twitchy and irritable, and can constrict the lumen of the airway. The net result is a generalised loss of airway calibre throughout the bronchial tree – a process known as bronchoconstriction – which leads to an obstruction to the flow of air into, and especially out of, the lungs. The obstruction is reversible, sometimes spontaneously, and sometimes with the aid of medications like salbutamol or terbutaline. 

Attacks or episodes of bronchoconstriction, or airway narrowing, can be induced by a variety of trigger factors, eg. exercise, viral upper respiratory tract infections, tobacco smoke, animal dander, dust mites, fumes and chemical sprays. Rarely, ingested substances such as aspirin, NSAIDs, carbonated drinks, tartrazine, sulphites, aspartame, metabisulphite, monosodium glutamate and food colourants can precipitate asthma episodes. Cold drinks or ice cream may also do so. Trigger factors will vary from person to person. Inflammation of the airway lining is usually a prerequisite, and predisposes asthma sufferers to symptoms when they encounter these environmental triggers.

Another important component of the asthma syndrome is bronchial hyperresponsiveness. If untreated the airways are more susceptible to bronchoconstriction when exposed to specific triggers. The more severe the condition, the more likely it is that the individual will respond to a given stimulus. The degree of this susceptibility to bronchoconstriction can be quantified by inhaling histamine or methacholine and taking measurements of lung function as part of a bronchial provocation test in a safely regulated clinical environment; this approach can be used for diagnosis of the condition

Prevalence and burden of disease 

In Ireland, in common with other developed countries, the prevalence of asthma has more than quadrupled between the 1980s and 2000. In 1983, a questionnaire was completed by almost three-thousand Irish schoolchildren (four to 19 years); this was repeated again nine years later in the same age group. The questionnaire screened children for asthma-like symptoms, eczema and hay fever. The researchers found that in 1983, asthma prevalence was 4.4%, and that over the subsequent decade, the rate had increased to 11.9%. 

More recent figures emerged from the International Study of Asthma and Allergic Conditions (ISAAC) studies, a series of large-population-based investigations using validated questionnaires designed to compare asthma prevalence between countries and to assess changes in epidemiology over time. Initially, children aged 13 to 14 years were studied, but younger groups, aged six to seven years, were subsequently included. The initial Irish study showed that asthma prevalence in 13 to 14-year-olds was 15.2% in 1995 and by 2007 had risen to 21.6%, a relative increase of 33%.² Ireland comes fourth in an international league table of asthma prevalence, behind Australia, New Zealand and the UK. Follow-up ISAAC studies have generally shown no significant increases in many areas, with existing high prevalence giving rise to some authorities suggesting that the prevalence is plateauing in these regions. However, increases have been observed in regions that had low prevalence rates in the initial assessment. 

In Ireland, the burden of asthma is high, with one in five Irish schoolchildren having asthma symptoms. The condition affects one-eighth of the general population, and it is estimated that there are 470,000 asthma sufferers in Ireland. There are 5,500 admissions every year; 55% are less than 14 years old. There are approximately 50 adult deaths per year due to asthma.³ Thirty per cent of these were less than 40 years of age. Fortunately, deaths in children from asthma are relatively rare, usually fewer than one per year. 

In a study published in 2005,⁴ four-hundred patients with current asthma in Ireland were interviewed in the Asthma Insights and Reality in Ireland (AIRI) survey to determine their healthcare utilisation, symptom severity, activity limitations and level of asthma control. Of those surveyed, acute services were utilised by a significant number of respondents. Over the previous year, 27% had either an emergency visit to the hospital or their general practitioner (GP), and 7% were hospitalised for asthma. In terms of asthma control, 19% experienced sleep disturbance at least once a week, 29% missed work or school, and 37% of respondents experienced symptoms during physical activity over the previous four-week period. Based on these findings, the level of asthma control and asthma management in Ireland falls well short of recommended national and international asthma guidelines.^4,5

Clinical presentation

Not all children with asthma will have the same symptoms. There can often be a preceding viral illness, with snuffles or cold-like symptoms. Symptoms will depend on the child’s age: for example, infants and toddlers won’t complain of exercise-related breathlessness, but will merely do less. 

The symptoms of asthma can reflect the underlying pathophysiology. Wheeze is the dominant symptom of asthma, but not all wheeze is due to asthma, and not every asthmatic wheezes. Wheeze is a whistling sound that occurs during exhalation; it is caused by airflow through narrowed bronchial tubes. Narrowing of the airway can be caused by conditions other than asthma. The GP will take a careful history and perform a physical examination in order to rule out the other less common possibilities.

One has to be careful about making a diagnosis of asthma in children under two years. Recurrent respiratory illness with wheeze is common in this age group, and the symptoms can be identical to those of asthma. However, we now know, from longitudinal population studies like the Tucson Children’s Birth Cohort, that the majority of these children are non-atopic wheezers, whose symptoms are only triggered by viral upper respiratory infection, and that the condition will subside by school age.

Sometimes wheeze will be associated with chest discomfort or even pain. Pre-school children don’t localise pain very well and, in this age group, abdominal pain may be a manifestation of asthma. 

Where cough is a symptom of asthma, it is usually dry, worse at night or on exertion. Cough may be the only symptom of asthma; however, clinicians are more reticent about making a diagnosis using only cough as the basis.

In older children who participate in more formal exercise, it may be noticed that they can’t keep up, or that they lack stamina. Sometimes these children opt for more sedentary pursuits, or, instead of playing midfield, prefer to play in goal, for example. It has been shown using accelerometers (devices which measure the number of footsteps) that asthmatic children are less active than their peers.

Exertional symptoms can reflect poor asthma control, yet exercise symptoms may dominate, and can occur against a background of generally good control. There is a specific form of asthma where exercise is the only trigger; this is termed exercise-induced asthma.

Differential diagnosis

Many, much rarer conditions can be associated with narrowing of the airway, and can produce wheeze and cough, thus mimicking asthma: inhaled foreign bodies (eg. peanut) often occur in a pre-school child. A history of choking will be present in only 50% of cases. Treatment involves removal of the foreign body by bronchoscopy. 

Cystic fibrosis (CF) is a life-shortening genetic condition of mucus-producing cells throughout the body. It principally affects the lungs, sweat glands and pancreas. It may present with cough, wheeze and breathlessness, which may be confused with asthma. Children with CF may also have loose stools and be underweight. The condition is diagnosed by sweat test. Newborn screening for CF in Ireland was introduced in July 2011.

In congenital airway abnormalities such as tracheomalacia or bronchomalacia, localised weakness of the airway wall leads to floppiness and collapse of the airway leading to wheeze.

Inherited immune deficiency is a disorder which predisposes affected children to respiratory infections and wheeze. The most common type is IgA deficiency, which affects one in 600 people; this is often associated with atopy and asthma. 

Primary ciliary dyskinesia: cilia are projections that extrude from respiratory cells; their function is to facilitate clearance of microbes and pollutants from both the upper and lower respiratory tracts. Rarely, in some children, these cilia fail to function correctly, and this may result in recurrent upper and lower respiratory tract infection. Primary ciliary dyskinesia is treated with chest physiotherapy, and respiratory infection is treated with antibiotics.

Bronchiectasis is a disease state defined by localised, irreversible dilation of part of the bronchial tree. It may be caused by a severe pneumonia, immune deficiency, CF or ciliary dyskinesia. 

Gastro-oesophageal reflux with aspiration is a condition where the contents of the stomach are passed back into the gullet (because of malfunction of the valve, or sphincter, between stomach and oesophagus) and then inhaled into the respiratory tract. Direct aspiration via fistula between trachea and oesophagus: very rarely, infants can be born with communications between the respiratory tract and the gullet, where formula can pass into the respiratory tract, leading to coughing and wheeze. Symptoms often occur after feeds. Surgical closure of the defect is required. 

Vocal cord dysfunction (VCD) is a condition that affects the vocal cords, characterised by full or partial vocal fold closure, which usually occurs during inhalation for short periods of time; however, they can occur during both inhalation and exhalation. VCD can produce an expiratory sound which may mimic asthma. The condition is diagnosed at laryngoscopy, and treatment usually consists of speech and language therapy.

Asthma diagnosis 

Asthma is usually diagnosed using the patient history and examination. Initially a history will be taken. The child’s height and weight should be measured and then plotted on a centile chart. In asthma these would be expected to be normal. The respiratory examination may be entirely normal. The hands are checked for finger clubbing which is observed in some chronic respiratory disorders but never in asthma. Sometimes, if the condition has persisted for a long time, there will be abnormalities of the chest wall. 

A pigeon-shaped breastbone (pectus carinatum) with in-drawing of the lower ribs (Harrison’s sulci) may be observed in some patients. Sometimes children with asthma have a hollow breastbone (pectus excavatum). There may be pallor, swelling and mucous coating of the lining of the nasal passages suggesting AR. Nasal polyps are quite rare in children with nasal allergy. The may be a transverse nasal crease due to constant rubbing of the nose. Frequently, examination with the stethoscope will be normal. However, during an asthma episode wheeze can be heard and breath sounds may be decreased in more severe attacks. Cyanosis of the lips and tongue may be apparent if the child is hypoxic. 

A peak-flow measurement can be taken in older, more co-operative children. The reading may be lower than expected for the child’s height, sex and age. If so, bronchodilators like Ventolin can be given to see if it improves. Sometimes a therapeutic trial of asthma treatment may be required in a younger child that is suspected to have asthma. 

Unfortunately there is no such thing as an asthma test. There are a number of additional tests that one can undergo to confirm a clinical suspicion of asthma. A chest x-ray is frequently normal or may show bronchial wall thickening and hyperinflation of the lungs. A CXR is not used to diagnose asthma but may, in some circumstances, help exclude conditions which may mimic asthma. The clinician may consider making a referral to a respiratory or allergy specialist who may order allergy or pulmonary function tests to facilitate the diagnostic process. 

Treatment

Therapy consists of three components: trigger avoidance, choosing the appropriate inhaler and optimising the inhaler technique and ensuring adherence to the prescribed medication. In the majority of cases asthma will be mild (step 1 or 2 of SIGN/BTS guidelines). Evidence-based guidelines are available to help clinicians manage asthma in a systematic way, eg. GINA, BTS/SIGN and PractALL. In these islands, the most commonly referred-to guidelines are the GINA and BTS/SIGN guidelines.

How is asthma control assessed?

The clinician will frequently use research-based treatment guidelines to assess and treat the child’s asthma.^5,6 These guidelines are updated regularly to keep up with advances in medicine. A useful self-administered test is the childhood asthma control test (http://www.asthmacontrol.com/child.html)⁷ which assesses asthma control over the previous four weeks in children aged either four to 12 years or older than 12 years.

The absence of symptoms, infrequent use of bronchodilator, normal exercise tolerance, normal pulmonary function and few missed schooldays are generally signs that asthma is well controlled. Infrequent or lack of exacerbations (asthma attacks) also suggests that asthma is under control. If asthma is under good control the clinician may attempt to step down the child’s controller medications. If control has been good for long periods, pulmonary function tests are normal and the patient is on minimal doses of preventative treatment, it may be decided to give the child a trial off therapy. 

The future

Many children will outgrow their asthma.¹ Some studies suggest that as many as two-thirds will remit by the teenage years. However, the condition can relapse later in adulthood during the third and fourth decades. Good prognostic features for remission include mild disease, absence of concurrent allergic conditions, male gender, normal lung function and virus-triggered asthma.

References

1. Greally P. Childhood Asthma: Your Questions Answered. Liberties Press Dublin, 2011
2. Kabir Z, Manning PJ, Holohan J, Goodman PG, Clancy L. Prevalence of symptoms of severe asthma and allergies in Irish school children: an ISAAC protocol study, 1995-2007
3. Asthma Society of Ireland. Available at: www.asthmasociety.ie
4. Manning PJ, Greally P, Shanahan E. Asthma Insights and Reality in Ireland. Ir Med J 2005; 98(10): 231-4
5. Scottish intercollegiate British Society asthma guidlines. Available at: www.sign.ac.uk/guidelines/fulltext/101/index.html) network
6. Diagnosis & Treatment of Childhood Asthma: a PRACTall consensus report. Allergy 2008; 63: 5-34
7. Child asthma control test. Available at: http://www.asthmacontrol.com/child.html