Diagnosing Childhood Asthma in Primary Care

• Asthma in children and in adults is a chronic inflammatory disease of the airways associated with widespread, variable outflow obstruction. The outflow obstruction is reversible either spontaneously or with medication. This inflammation is associated with bronchial hyper-responsiveness (BHR) or airway hyperreactivity to a variety of stimuli (eg environmental allergens and irritants).
• The diagnosis is a clinical one with no single diagnostic test, only corroboration of the diagnosis with changes in lung function
• The diagnosis is difficult in children because it is often not possible to measure lung function but also because other common conditions can produce similar symptoms
• It is a common condition with significant morbidity and mortality which is diagnosed according to identification of key clinical features, regular review and response to treatment
• Accurate diagnosis in primary care is an important challenge.

• The prevalence in a study from the west of Scotland was up from 3% in 1972-6 to 8.2% in 1996.¹ The prevalence in this and other studies appears to be increasing as it is in other countries. In the United States studies show a 40% increase in the last decade with a typical prevalence of 7.2%.² A recent study shows less clear cut increases in prevalence around the world.³
• Morbidity and mortality are increasing too despite advances in treatment
• The prevalence is 8-10 times higher in developed countries than in developing countries
• Prevalence is higher in lower socioeconomic groups in urban areas
• There are gender differences. Boys are affected more before puberty (3 times greater prevalence). Prevalence is equal in adolescence, but adult onset asthma is more common in women.⁴
• Asthma develops usually before age 5 years and in many before age 3 years.

There is a long list of possible risk factors.^5,6 Awareness of these is useful when taking the history and planning management.

• Personal or family history of asthma or atopy ⁷
• Triggers e.g.allergens (such as pollens, animal dander), dust, exercise, viruses, chemicals, weather changes, emotional factors, irritants and smoke⁸
• Urban environment⁹
• Socioeconomic stresses¹⁰
• Obesity⁴
• Prematurity and low birth weight
• Virus infections in early childhood
• Maternal smoking
• Smoking¹¹
• Early exposure to broad spectrum antibiotics¹²
• Reduced in breast fed babies¹³
• Male sex for asthma in prepubertal children
• Female sex for persistence of asthma into adulthood

Symptoms

Symptoms include wheeze, cough, chest tightness and dyspnoea.⁵ These symptoms are usually variable (according to severity), intermittent, worse at night, and provoked by triggers (eg. exercise):

• Wheeze. Very common, high-pitched, polyphonic and present in expiration. As severity increases may be throughout expiration and then also during inspiration. However in the most severe episode it may be absent. May be absent when smaller airways involved. Distinguish from the inspiratory, monophonic noise of stridor associated with reduced or impaired upper airway patency.
• Cough. This 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.
• Chest tightness with or without other symptoms occurs, particularly with exercise and at night in asthma.
• Breathlessness varies according to severity. 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.

Signs

Signs will vary according to severity of asthma and severity of any exacerbation.^6,5 The following illustrates how signs change with increasing severity:

• It is very common for there to be no signs
• Mild episode: respiratory rate (RR) increased. Accessory muscles of respiration not used. Pulse rate <100. Pulsus paradoxus absent. Wheeze moderate and often end inspiratory.
• Moderate episode: RR increased. Accessory muscles used. Pulse rate 100-120. Loud expiratory wheeze. Pulsus paradoxus may be present (10-20 mm Hg).
• Severe episode: RR>30, accessory muscles of respiration used. Pulse rate >120. Loud inspiratory and expiratory wheeze. Pulsus paradoxus (20-40 mm Hg).
• Status asthmaticus: Paradoxical thoracolumbar movement, wheezing may be absent (silent chest). Severe hypoxia may be associated with bradycardia.

Severity of asthma

This can be classified^14,15 as:

• Mild intermittent. Symptoms fewer than twice per week and pulmonary function normal between exacerbations which are brief (few hours to a few days). Night symptoms less than twice per month. Peak expiratory flow rate (PEF) variation less than 20%.
• Mild persistent asthma. Symptoms more than twice per week but less than once a day. Exacerbations may affect activity. Night symptoms more than twice per month. PEF less than 80% of predicted and variation in PEF 20-30%.
• Moderate persistent asthma. Daily symptoms and daily use of relieving inhalers. Exacerbations more than twice weekly and last for days. Exacerbations affect activity and night symptoms occur more than once per week. PEF 60%-80% of predicted, variability in PEF greater than 30%.
• Severe persistent asthma. Continuous or frequent symptoms, limited physical activity, frequent night symptoms with PEF less than 60% of predicted and PEF variability greater than 30%.

Note:

• Asthma is assigned to the most severe category even if only one feature from that category
• The variable nature of asthma means there will be overlap between categories over time.
• Exacerbations themselves may be mild, moderate or severe
• PEF testing is important in assessing severity^16,15

This should be founded on^5,17,18,19:

• Presence of certain key presenting features (see above):
  • Wheeze. Suspect asthma in a child with wheezing, preferably heard by a health professional at auscultation to distinguish particularly from upper airway noises.
  • Dry cough
  • Breathlessness (dyspnoea)
  • Tight chest
  • Noisy breathing
  • Characteristic pattern of illness: variability of symptoms; intermittent; worse at night; provoked by triggers (exercise etc as above)
  • Severity:as above
• Consideration of the differential diagnosis as below
• Response to trial of treatment
• Follow up and repeat assessment, again giving consideration to alternative diagnosis if treatment fails.
• If treatment works and the diagnosis seems likely, then an Asthma Action Plan can be made.

• 20% or greater variability of PEF (minimum 60 l/min change) for 3 days/week for 2 weeks is highly suggestive of asthma. Note: smaller %age variability does occur with asthma.
• Increase of PEF(20% and minimum 60 l/min) after short acting β-agonist
• Increase PEF (20% and minimum 60 l/min) after trial of prednisolone 30mg/day for 14 days
• Decrease (20% and minimum 60 l/min) with exercise for 6 minutes. Readings taken every 10 minutes for 30 minutes.
• FEV1 can be used but change of 15% and at least 200mls taken as significant.

Diagnosis in general practice does not, as described above, rely on the results of investigations. However:

• Pulmonary function tests (including PEF) are unreliable in patients under 5 years
• Exercise testing. This can only be performed in patients of an appropriate age (over 6 years) and is not often used in general practice
• FBC (eosinophilia) and IgE levels may help where allergy is suspected
• CXR is performed if asthma does not respond to initial therapy. Findings in asthma can include hyperinflation and increased bronchial markings. It may help with differential diagnosis (for example parenchymal disease, pneumonia, atelectasis, foreign body, congenital anomalies) as well as in diagnosing complications (for example pneumothorax).
• Allergy testing should not be performed in general practice
• Referral for further investigation may be indicated.

These include:⁵

• Diagnosis unclear or in doubt
• Symptoms present from birth or perinatal lung problem
• Excessive vomiting/possetting
• Severe upper respiratory tract infection
• Persistent wet cough
• Family history of unusual chest disease
• Failure to thrive
• Unexpected clinical findings (for example focal chest signs, abnormal cry or voice, dysphagia, stridor)
• Failure to respond to conventional treatment (especially corticosteroids above 400 mcg/ day)
• Frequent use of oral steroids
• Parental concerns or anxiety
• Food allergies with asthma. These patients are high risk and should be referred.

Confirmation of diagnosis involves initiating treatments and then following up with further assessment and review of the diagnosis. However links to asthma management and the BTS guidance⁵ give more detail.

Remember when making the diagnosis that:

• Children who have mild asthma in childhood are more likely to remit or to continue with mild symptoms into adulthood. The earlier the onset of wheeze, the better the prognosis. Children diagnosed before 2 years are more likely to become asymptomatic in later life.^5,6,19
• Early allergic sensitisation is a risk factor for persistent asthma. Certain early exposures, including older siblings, day care attendees, pets, farm animals, and house-dust endotoxin, seem to decrease the risk for persistent asthma.^5,6,19

Remember when taking the history to make the diagnosis that thought should be given to possible prevention⁵ For example:

1. Primary prevention:
   • Smoking cessation in parents and future parents
   • Encourage breastfeeding
2. Secondary prevention:
   • In committed families different approaches to reduce house dust mite exposure
   • Removal of pets from the home is recommended when allergic
   • Weight loss for obese patients