Asthma is a relatively common condition that is characterised by at least partially reversible inflammation of the airways and reversible airway obstruction due to airway hyper-reactivity. It can be acute, subacute or chronic.
Asthma is one of the most common chronic diseases in the world. According to the 2014 Global Asthma Report it is estimated that around 300 million people in the world have asthma 17 and the estimated mean prevalence of clinical asthma in the UK is 16% ref needed.
Asthma may occur at any age, but most patients with asthma experience their first symptoms before age 5.
The classical symptoms of asthma are wheeze, shortness of breath, chest tightness or difficulty breathing and cough. These symptoms are typically variable and can be absent for long periods of time, with possible episodic exacerbations often triggered by factors such as exercise, allergen or irritant exposure, cold air or viral respiratory infections.
The diagnosis of asthma is clinical and relies on the recognition of a characteristic pattern or respiratory symptoms and signs in the absence of an alternative explanation. Features that increase the probability of asthma are:
- more than one of the following symptoms: wheeze, cough, difficulty breathing and chest tightness
- episodic symptoms that are worse at night and in the early morning, and occur in response to certain triggers, e.g. exercise, allergen exposure, cold air
- personal history of atopic disorder or family history of atopic disorder and/or asthma
- widespread wheeze on auscultation
Lung function tests are useful in the evaluation of a patient with asthma to assess the presence, severity and reversibility of the airflow obstruction. On spirometry an FEV1/FEV ratio less than 0.7 confirms obstruction. In asthmatic patients, there is usually a large bronchodilator response (typically an increase of at least 12-15% in FEV1) 3, and it is also typical an abnormally high variability of the peak expiratory flow. A normal spirometry, particularly if performed when the patient is asymptomatic, does not exclude the diagnosis of asthma.
Additional investigations such as tests of atopy (blood eosinophil count, serum IgE and allergen skin prick tests) may be of value in selected patients.
Inflammation plays a major role in asthma and involves multiple cell types and mediators. The factors that initiate the inflammatory process are complex and still under investigation. Genetic factors (such as cytokine response profiles) and environmental exposures (such as allergens, pollution, infections, microbes, stress) at a crucial time in the development of the immune system are known to be involved.
It mainly involves the medium sized and small bronchi 6.
Asthma is histologically characterised by the presence of chronic inflammation of the airways. The bronchi are thickened by a combination of oedema, bronchial wall smooth muscle hyperplasia and an increase in the size of the mucous glands associated with the airways. Crystalline granules called Charcot-Leyden crystals form in eosinophils. Spiral-shaped mucous plugs (Curschmann's spirals) are seen in the sputum 15.
Plain chest radiographs can be normal in up to 75% of patients with asthma.
Reported features with asthma include:
- pulmonary hyperinflation
- bronchial wall thickening: peribronchial cuffing (non-specific finding but may be present in ~48% of cases with asthma 1)
- pulmonary oedema (rare): pulmonary oedema due to asthma (usually occurs with acute asthma)
CT is usually used to detect the presence of complicated associated conditions such as allergic bronchopulmonary aspergillosis (APBA) and not to directly diagnose asthma.
Reported HRCT features of asthma are non-specific as individual features, they include 2:
- bronchial wall thickening 2-3
- expiratory air trapping
- inspiratory decreased lung attenuation
- small centrilobular opacities 6,8
- bronchial luminal narrowing: reduced bronchoarterial-diameter ratio 7
- subsegmental bronchiectasis: may be present in ~28-62% of asthmatics 8,12
Treatment and prognosis
The goal of the treatment is to control the symptoms, prevent exacerbations and loss of lung function and reduce associated mortality.
Drugs used for control of asthma depend on the severity of the disease. Short-acting β2-agonists can be used in patients with mild occasional symptoms. Inhaled steroids (oral steroids might be required in severe cases) and long-acting β2-agonists can be used for long-term control. Oxygen, short-acting β2-agonists, inhaled anticholinergics and systemic steroids are used in acute exacerbations.
Mechanical ventilation may be necessary for severe exacerbations that do not respond to medical treatment. Non-pharmacological measures, such as smoking cessation and avoidance of occupational sensitizers, are also important.
Asthma is a disease with variable progression and severity of symptoms over time. The prognosis depends on the severity of the disease and the degree of control with treatment. Some patients can be symptom-free for long periods, whereas a few patients with severe persistent asthma develop progressive loss of lung function. Death due to asthma is very rare.
There are several conditions that can complicate asthma; they include 1,6,16:
- 1. Lange S. Radiology of Chest Diseases. Thieme Medical Publishers. (1998) ISBN:1588904474. Read it at Google Books - Find it at Amazon
- 2. Jensen SP, Lynch DA, Brown KK et-al. High-resolution CT features of severe asthma and bronchiolitis obliterans. Clin Radiol. 2003;57 (12): 1078-85. Pubmed citation
- 3. Montaudon M, Lederlin M, Reich S et-al. Bronchial measurements in patients with asthma: comparison of quantitative thin-section CT findings with those in healthy subjects and correlation with pathologic findings. Radiology. 2009;253 (3): 844-53. Radiology (full text) - doi:10.1148/radiol.2533090303 - Pubmed citation
- 4. Hodson ME, Simon G, Batten JC. Radiology of uncomplicated asthma. Thorax. 1974;29 (3): 296-303. Free text at pubmed - Pubmed citation
- 5. Newcomb P, Cyr A. Conditions associated with childhood asthma in north Texas. ISRN Allergy. 24;2012: 823608. ISRN Allergy (full text) - doi:10.5402/2012/823608 - Free text at pubmed - Pubmed citation
- 6. Silva CI, Colby TV, Müller NL. Asthma and associated conditions: high-resolution CT and pathologic findings. AJR Am J Roentgenol. 2004;183 (3): 817-24. doi:10.2214/ajr.183.3.1830817 - Pubmed citation
- 7- Park CS, Müller NL, Worthy SA et-al. Airway obstruction in asthmatic and healthy individuals: inspiratory and expiratory thin-section CT findings. Radiology. 1997;203 (2): 361-7. Radiology (abstract) - Pubmed citation
- 8. Grenier P, Mourey-Gerosa I, Benali K et-al. Abnormalities of the airways and lung parenchyma in asthmatics: CT observations in 50 patients and inter- and intraobserver variability. Eur Radiol. 1996;6 (2): 199-206. Pubmed citation
- 9. Laurent F, Latrabe V, Raherison C et-al. Functional significance of air trapping detected in moderate asthma. Eur Radiol. 2001;10 (9): 1404-10. Pubmed citation
- 10. Newman KB, Lynch DA, Newman LS et-al. Quantitative computed tomography detects air trapping due to asthma. Chest. 01;106 (1): 105-9. doi:10.1378/chest.106.1.105 - Pubmed citation
- 11. Lynch DA, Newell JD, Tschomper BA et-al. Uncomplicated asthma in adults: comparison of CT appearance of the lungs in asthmatic and healthy subjects. Radiology. 1993;188 (3): 829-33. Radiology (abstract) - Pubmed citation
- 12. Takemura M, Niimi A, Minakuchi M et-al. Bronchial dilatation in asthma: relation to clinical and sputum indices. Chest. 01;125 (4): 1352-8. doi:10.1378/chest.125.4.1352 - Pubmed citation
- 13. Beasley R, Burgess C, Crane J et-al. Pathology of asthma and its clinical implications. J. Allergy Clin. Immunol. 1993;92 (1 Pt 2): 148-54. Pubmed citation
- 14. Barnes PJ, Drazen JM, M.D. SIR et-al. Asthma and COPD. Academic Press. (2009) ISBN:0123740010. Read it at Google Books - Find it at Amazon
- 15. Goljan EF. Rapid Review Pathology. Saunders. ISBN:0323087876. Read it at Google Books - Find it at Amazon
- 16. Stack AM, Caputo GL. Pneumomediastinum in childhood asthma. Pediatric emergency care. 12 (2): 98-101. Pubmed
- 17. The Global Asthma Report 2014. Auckland, New Zealand: Global Asthma Network, 2014. http://www.globalasthmareport.org/resources/Global_Asthma_Report_2014.pdf [accessed 12th October 2017]