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Asthma versus COPD: what is the difference?

Both asthma and chronic obstructive pulmonary disease (COPD) are chronic diseases characterised by airflow obstruction, and result from underlying airway inflammation. Whereas the airflow obstruction is reversible in asthma, in COPD it is at best only partially reversible. The inflammation in asthma is mediated by T-lymphocytes and eosinophils, but in COPD the neutrophil is the dominant inflammatory cell. Long-standing, poorly controlled asthma may evolve to fixed airflow obstruction, and thus be indistinguishable from COPD. Conversely, some patients with COPD may have partial (but significant) reversibility and respond to corticosteroids, and their condition may therefore resemble asthma to some degree.

There are no bedside or commercially available tests that directly and reliably measure the nature of airway inflammation in these two conditions. To differentiate asthma from COPD one is dependent on the history, clinical examination during the stable phase, and demonstration of the degree of airflow reversibility in response to administration of a short-acting [[beta].sub.2]-agonist and/or corticosteroid.

History

Asthma usually presents in childhood; however, adult-onset asthma is not uncommon. Frequently there is a family history of atopy. COPD presents in adulthood, usually in persons >40 years of age. In most cases, there is a strong history of smoking (cigarettes, cannabis).

The usual symptoms are cough, wheeze and dyspnoea. In asthma the cough is minimally productive and typically worse at night. Patients with COPD are more likely to have a productive cough, usually of mucoid sputum, which is worse in the morning.

In both conditions exacerbation of symptoms is often worsened by infections. Viral infections, in particular, are common precipitants, but about half of COPD exacerbations are related to bacterial infections. Other causes of acute asthma attacks are exposure to dust, smoke, pollen, animal dander, drugs (e.g. [beta]-blockers, aspirin), exercise, cold weather, and occupational exposures. Acute exacerbations of COPD may be precipitated by air pollution, cold weather and pulmonary thrombo-emboli.

Clinical features

During acute exacerbations it may be difficult to distinguish asthma from COPD. In both diseases patients show signs of respiratory distress with hyperinflation of the chest. Audible wheezing or a silent chest may be present.

In the stable state, examination of the patient with asthma is unremarkable. Evidence of atopic disease (e.g. allergic rhinitis) may be present. However, the COPD patient frequently demonstrates pursed lip breathing, tachypnoea at rest, chest hyperinflation, decreased intensity of breath sounds, and crackles on auscultation. There may also be evidence of chronic hypoxaemia and pulmonary hypertension (plethora, cyanosis, cor pulmonale).

Lung function tests: Peak expiratory flow (PEF), spirometry

Asthma patients should achieve normal lung function, whereas COPD patients demonstrate persistent airflow obstruction ([FEV.sub.1]/FVC <70% on spirometry) even when at their best.

All patients with evidence of airflow obstruction (on PEF measurement or spirometry) suspected to be caused by asthma or COPD should undergo assessment for airflow reversibility. This should be done by the administration of a short-acting [[beta].sub.2] agonist, e.g. salbutamol 200-400 [micro]g (via metered-dose inhaler or nebuliser), followed by repeat PEF measurement or spirometry 20 minutes later. Clinically significant reversibility is indicated by a PEF measurement that increases by 20% from baseline, or by spirometry where the [FEV.sub.1] increases by at least 12% from baseline together with an absolute increase of 200 ml or more. However, it must be noted that these criteria are not useful if the baseline value is only mildly abnormal and may erroneously lead to underestimation of reversibility.

If this post-bronchodilator lung function does not normalise, patients should be subjected to a trial of corticosteroid therapy (prednisone 40 mg daily for 2 weeks, or inhaled budesonide 400 [micro]g bd or equivalent for 6 weeks). Restoration of lung function to normal is in keeping with a diagnosis of asthma, but partial improvement is more indicative of COPD.

If the patient has normal lung function at consultation, but has symptoms of asthma, demonstration of exaggeration of the normal diurnal variation of PEF is useful. Patients should record PEF measurements in the morning and evening. Variability of >20% is highly suggestive of asthma. Another simple test to demonstrate airway hyperresponsiveness is to determine PEF measurements before and 10 minutes after 6 minutes of exercise. A decrease in PEF of 20% or more (or a 15% fall in [FEV.sub.1]) precipitated by exercise is also suggestive of asthma. It is important to be aware that other causes of hyperresponsiveness do exist. These include recent viral lower respiratory tract infections in patients without asthma (for up to 6 weeks).

Clinical importance of distinguishing asthma from COPD

Untreated or inadequately treated airflow obstruction results in avoidable morbidity and impaired quality of life. Early detection of COPD affords an opportunity to encourage smoking cessation and reduce long-term consequences. All asthma patients must be prescribed inhaled corticosteroid therapy. However, only COPD patients who display a clinically significant response to corticosteroids or who have three or more acute exacerbations per year have been shown to benefit from maintenance inhaled corticosteroid therapy. Unnecessary prescription of these drugs results in increased morbidity and unwarranted health care costs.

Bibliography

COPD Guideline Working Group of the South African Thoracic Society. Guideline for the management of chronic obstructive pulmonary disease (COPD): 2004 revision. S Afr Med J 2004: 94(7): 559-575.

Lalloo U, Ainslie G, Wong M, et al. Guidelines for the management of chronic asthma in adolescents and adults. SA Fam Pract 2007; 49(5): 19-31.

M L WONG, MB BCh, DCH (SA), FCP (SA), FCCP, FRCP (Lond)

Principal Specialist and Head, Division of Pulmonology, Chris Hani Baragwanath Hospital, Johannesburg

Senior Lecturer, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg
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Title Annotation:More about ... Asthma; chronic obstructive pulmonary disease
Author:Wong, M.L.
Publication:CME: Your SA Journal of CPD
Article Type:Report
Geographic Code:6SOUT
Date:Apr 1, 2008
Words:940
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