Diagnosing childhood asthma in primary care

What is childhood asthma?

Asthma is a chronic inflammatory disease of the airways, associated with widespread, variable outflow obstruction. Clinically, this manifests as:¹

• Wheeze.

• Cough.

• Difficulty breathing.

• Chest tightness.

The outflow obstruction reverses either spontaneously or with medication. The underlying inflammation is associated with bronchial hyper-responsiveness (BHR) or airway hyper-reactivity to a variety of stimuli (for example, environmental allergens and irritants).

Diagnosis of asthma in children is difficult because of the complex nature of the disorder in the young, and because younger children may not be able to perform objective diagnostic tests. Accurate diagnosis in primary care remains an important challenge.

Many people consider 'wheeze' synonymous with asthma, yet there are many different causes of wheeze in childhood and increasingly we recognise different 'phenotypes' of wheezing. These are usually determined retrospectively, as they depend on the pattern of symptoms over time:

• Episodes of wheezing, cough and difficulty breathing associated with viral upper respiratory tract infections (URTIs) with no persisting symptoms - this is known as 'viral-induced wheeze'. Common in infants and preschool children (about 30% of children aged under 3 years). Most, however, will have stopped having recurrent symptoms by school entry.

• Some children who wheezed early, will go on to develop wheezing with other triggers so that they develop interval symptoms, similar to older children with classical atopic asthma.²

• Atopic asthma is more common in school-aged children; symptoms occur often with identifiable triggers and often alongside eczema or hay fever but, even in this age group, non-atopic asthma is as frequent as the atopic variant.

The National Institute for Health and Care Excellence (NICE) guidelines recommend that asthma diagnoses made on clinical grounds alone are termed 'suspected asthma', and that an asthma diagnosis should only be confirmed if corroborated with at least one positive objective test. In under 5s, diagnosis is particularly difficult as it is difficult for children to do the tests, and there are no good reference standards - objective testing should be attempted from age 5 onwards.

How common is childhood asthma? (Epidemiology) ³⁴

Asthma affects more than 300 million people worldwide and 11.6% of children aged 6-7 years.

Asthma is the commonest long-term condition in children and is more common in children than adults. In the UK there are currently 1.1 million children receiving asthma treatment, which is 1 in 11 children. In childhood, asthma is more common in boys than girls.

The UK has one of the highest mortality rates in Europe for children and young people with asthma as the underlying cause. In 2017, there was a small reduction in the total number of deaths due to asthma.

Emergency admissions for asthma have fallen since 2003-4, but there is wide variation across the UK with the highest rates occurring in areas of deprivation. This is thought to be because these children have greater levels of exposure to tobacco smoke and environmental pollution. In England in 2017, children in the most deprived areas were 2.5 times more likely to be admitted to hospital with asthma than children in the least deprived areas.

Risk factors³⁵

There is a long list of possible risk factors, which includes:

• Personal history of atopy.

• Family history of asthma or atopy.

• Triggers (for example, allergens such as pollens, animal dander), dust, exercise, viruses, chemicals, weather changes, emotional factors, irritants and smoke.

• Urban environment.

• Socio-economic stresses.

• Obesity.⁶

• Prematurity and low birth weight.

• Viral infections in early childhood.

• Maternal smoking.

• Passive as well as active smoking.

• In vitro fertilisation.

• Early exposure to broad-spectrum antibiotics. ⁷

Breast-feeding possibly confers protection.⁸

Risk factors for persistence of wheezing and asthma throughout childhood include:⁹

• Age at presentation - those presenting aged younger than 2 years tend to have become asymptomatic by mid-childhood.

• Co-existing atopy is a risk factor for persistence of asthma.

• Family history of atopy, particularly maternal atopy.

• Sex - male sex is a risk factor for asthma in prepubertal children whilst female sex is a risk factor for persistence of asthma into adulthood. Girls are less likely to 'grow out' of their asthma.

• More severe and frequent wheezing episodes are associated with asthma persisting into adolescence.

• Abnormal lung function, both baseline airway function and increased airways responsiveness.

A simple tool has been validated for predicting asthma at school age in preschool children with wheeze or cough. The tool consists of ten predictors yielding a total score between 0 and 15: sex, age, wheeze without colds, wheeze frequency, activity disturbance, shortness of breath, exercise-related and aeroallergen-related wheeze/cough, eczema and parental history of asthma/bronchitis.¹⁰

Symptoms of childhood asthma (presentation)⁵

Clinical features that increase the probability of the diagnosis of asthma in children:⁹

• More than one of the following symptoms - wheeze, cough, difficulty breathing, chest tightness, particularly if these symptoms:

  • Are frequent and recurrent.

  • Are worse at night and in the early morning.

  • Occur in response to, or are worse after, exercise or other triggers, such as exposure to pets, cold or damp air, or with emotions or laughter.

  • Occur apart from colds.

• Personal history of atopic disorder.

• Family history of atopic disorder.

• Widespread wheeze heard on auscultation.

• History of improvement in symptoms or lung function in response to adequate therapy.

Symptoms

When taking a history:

• Ask about typical symptoms:
  

  • Wheeze - very common, high-pitched, polyphonic and present in expiration. As severity increases, it may be present during expiration and inspiration. In the most severe episode, it may be completely absent. It must be distinguished from the inspiratory, monophonic noise of stridor which is associated with reduced or impaired upper airway patency. Note that parental understanding of wheeze may include whistling, squeaking or gasping sounds, or a different style, rate or timbre of breathing. Clarify what a patient or their parent means by wheeze.

  • Cough may be the only symptom in children (particularly with exercise-induced asthma and nocturnal asthma). The cough is usually dry and nonparoxysmal. The nocturnal cough of asthma usually occurs after midnight. About 10% of preschool children have chronic cough without wheeze at some time. Chronic cough on its own is a poor marker for asthma and one should always consider other diagnoses. Children with cough-predominant asthma should show improvement on a short trial of asthma medication and return of symptoms on discontinuation of treatment.

  • Chest tightness with or without other symptoms occurs, particularly with exercise and at night in asthma.

  • Breathlessness varies according to severity. Establish whether the child is able to play, run or walk. The most severe attacks are accompanied by breathlessness at rest, paucity of speech, agitation, feeding difficulties and attenuated cry (in infants). Children become drowsy and confused and, in adolescents particularly, symptoms develop late as severity increases.

• Identify triggers - for example, viral URTIs, cold air, dust, pets, pollen, change in weather, exercise.

• Ask about symptoms in the intervals between exacerbations.

• Establish what the pattern has been over time and the current frequency of acute episodes.

• Ask about atopic illnesses in the patient and their family.

• Check previous diagnoses, treatment and concordance with treatment.

• Check for previous emergency contacts with healthcare professionals with related symptoms.

• Note what impact there has been on the child's life and how much school has been missed.

Signs

Signs will vary according to the severity of asthma and the severity of any exacerbation. During episodes, check for:

• Widespread wheeze.

• Increased work of breathing.

• Pulse rate.

• Respiratory rate.

• Oxygen saturation.

• Peak expiratory flow rate (PEFR) - in children aged over 5 years.

• Response to bronchodilator therapy.

Between episodes, there may be no clinical signs but check for:

• Hyperexpansion and Harrison's sulci.

• Clues to other possible diagnoses.

Differential diagnosis⁵⁹

Clues to alternative diagnoses in the wheezy child

Wheeze present from birth:

• Presents immediately, constant wheeze without variation: structural abnormality - for example, bronchogenic cyst, vascular ring.

• Weak cry, stridor: laryngeal abnormality.

• Signs of heart failure: congenital heart disease.

Wheeze present shortly after birth:

• History of prematurity or ventilation: bronchopulmonary dysplasia.

• Recurrent bacterial infections and failure to thrive (FTT): immunodeficiency.

• Persistent cough and FTT, family history of chest disease: cystic fibrosis.

• Persistent nasal discharge and otitis media: ciliary dyskinesia.

• Vomiting and aspiration: gastro-oesophageal reflux disease (GORD).

Sudden onset in a previously well child:

• History of choking, unilateral reduced breath sounds: foreign body.

• Persistent wet cough: cystic fibrosis, bronchiectasis, recurrent aspiration, immunodeficiency, ciliary dyskinesia.

• FTT: cystic fibrosis, immunodeficiency, GORD.

• Finger clubbing, purulent sputum: cystic fibrosis, bronchiectasis.

• Focal signs in the chest: developmental anomaly, post-infection, bronchiectasis, tuberculosis, foreign body.

Investigations¹

NICE recommends performing objective tests from the outset if asthma is suspected on clinical grounds, although treatment may be started immediately if the patient is acutely unwell or highly symptomatic at presentation - in which case, objective testing should be performed as soon as practicable, as spirometry and FeNO testing may be affected by the use of inhaled corticosteroids.

The exception is under 5s, in whom objective testing is often not possible.

NICE recommends the following strategy for confirming an asthma diagnosis:

Children aged 5 to 16

• Measure the FeNO level in children with possible asthma. Diagnose asthma if the FeNO level is 35 ppb or more.

• If FeNO levels are normal, or FeNO is not available, measure bronchodilator responsiveness with spirometry. Diagnose asthma if the FEV1 increase is 12% or more from baseline, or if the FEV1 increase is 10% or more of the predicted normal FEV1.

• If spirometry is not available or delayed, measure peak expiratory flow (PEF) twice daily for 2 weeks. Diagnose asthma if PEF variability, expressed as amplitude percentage mean, is 20% or more.

• If asthma is not confirmed by FeNO, BDR, or PEF variability, but is still suspected clinically, either perform skin prick testing to house dust mite or measure total IgE level and blood eosinophil count.

  • If there is no evidence of sensitisation to house dust mite on skin prick testing, or if the total serum IgE is not raised, asthma is excluded.

  • Diagnose asthma if there is evidence of house dust mite sensitisation, or if the total serum IgE level is raised and the eosinophil count is more than 0.5 x 10⁹ per litre.

• If there is still diagnostic doubt, refer to a paediatric specialist for a second opinion and consideration of a bronchial challenge test.

Children aged under 5

• Treat with inhaled corticosteroids as per NICE's recommendations (see Management of childhood asthma) and review the child regularly.

• If symptoms are still present at age 5, attempt objective testing as outlined above.

• If the child is unable to perform objective testing at age 5, re-attempt the tests every 6 to 12 months until satisfactory results are obtained, and refer for specialist assessment if they are not responding to treatment.

• Refer to a respiratory paediatrician if a preschool child has any hospital admissions with wheeze, or if they have attended an emergency department with wheeze two or more times in a 12-month period.

Indications for referral ¹⁹

These include:

• Diagnosis unclear or in doubt.

• Symptoms present from birth or a perinatal lung problem.

• Excessive vomiting/possetting.

• Severe URTI eg bronchiolitis, croup, epiglottitis.

• Persistent wet cough.

• Family history of unusual chest disease.

• Faltering growth (previously called failure to thrive - FTT.

• Nasal polyps.

• Unexpected clinical findings (for example, focal chest signs, abnormal cry or voice, dysphagia, stridor).

• Failure to respond to conventional treatment (especially corticosteroids above 400 micrograms/day). Vocal cord dysfunction can mimic steroid-refractory asthma.

• Frequent use of oral steroids.

• Parental concerns or anxiety.