Treatment Of: January 2011

Asthma : Management - Management of catastrophic sudden severe (brittle) asthma - Prognosis

Asthma
"Management - Management of catastrophic sudden severe (brittle) asthma - Prognosis"

Management
The aims of treatment are to:
■ abolish symptoms
■ restore normal or best possible lung function
■ reduce the risk of severe attacks
■ enable normal growth to occur in children
■ minimize absence from school or employment.

This involves:
■ patient and family education about asthma
■ patient and family participation in treatment
■ avoidance of identified causes where possible
■ use of the lowest effective doses of convenient medications to minimize short-term and long-term side-effects.
Many asthmatics belong to self-help groups whose aim is to further their understanding of the disease and to foster self-confidence and fitness.

Control of extrinsic factors
Measures must be taken to avoid causative allergens such as pets, moulds and certain foodstuffs (see allergic rhinitis), particularly in childhood. Avoidance of the house-dust mite is very difficult. A recent Cochrane review confirms earlier data that there is no evidence for the effectiveness of physical or chemical measures to control house-dust mite levels. The use of covers for bedding and changes to living accommodation has no beneficial effect on outcomes Active and passive smoking should be avoided, as should betablockers in either tablet or eye drop form. Individuals intolerant to aspirin should avoid all NSAIDs. Other agents (e.g. preservatives and colouring materials such as tartrazine) should be avoided if shown to be a causative factor. Fifty per cent of individuals sensitized to occupational agents may be cured if they are kept permanently away from exposure. The remaining 50% continue to have symptoms that may be as severe as when exposed to materials at work, especially if they were symptomatic for a long time before the diagnosis was made.
This emphasizes that:
■ The rapid identification of extrinsic causes of asthma and their removal is necessary wherever possible (e.g. occupational agents, family pets).
■ Once extrinsic asthma is initiated, it may become selfperpetuating, possibly by non-immune mechanisms.

Drug treatment
The mainstay of asthma therapy is the use of therapeutic agents delivered as aerosols or powders directly into the lungs (Practical box). The advantages of this method of administration are that drugs are delivered direct to the airways and first-pass metabolism in the liver is avoided; thus lower doses are necessary and systemic unwanted effects are minimized.
  Practical Box Inhaled therapy
Patients should be taught how to use inhalers and their technique checked regularly.

Use of a metered-dose inhaler
1. The canister is shaken.
2. The patient exhales to functional residual capacity (not residual volume), i.e. normal expiration.
3. The aerosol nozzle is placed to the open mouth.
4. The patient simultaneously inhales rapidly and activates the aerosol.
5. Inhalation is completed.
6. The breath is held for 10 seconds if possible. Even with good technique only 15% of the contents is inhaled and 85% is deposited on the wall of the pharynx and ultimately swallowed.

NB Chlorofluorocarbon (CFC) propellants have been/are being replaced by hydrofluoralkane (HFA) propellants. The new aerosols may feel and taste different and patients need reassurance of their efficacy.

Spacers
These are plastic conical spheres inserted between the patient’s mouth and the inhaler. They are designed to reduce particle velocity so that less drug is deposited in the mouth. Spacers also diminish the need for coordination between aerosol activation and inhalation. They are useful in children and in the elderly and they reduce the risk of candidiasis.
Both national and international guidelines have been published on the stepwise treatment of asthma (previous Box) based on three principles:
■ Asthma self-management with regular asthma monitoring using PEF meters and individual treatment plans discussed with each patient and written down.
■ The appreciation that asthma is an inflammatory disease and that anti-inflammatory (controller) therapy should be started even in mild cases.
■ Use of short-acting inhaled bronchodilators (e.g. salbutamol and terbutaline) only to relieve breakthrough symptoms. Increased use of bronchodilator treatment to relieve increasing symptoms is an indication of deteriorating disease.
A list of drugs used in asthma is shown in next Box. These are given in a stepwise fashion (1 to 6) as indicated in previous Box.
Once the asthma is under control, for at least 2–3 months, the drug therapy should be re-assessed in order to use the minimal dosage of inhaled steroids, combined with an oral long-acting β2 agonist (stepdown). These agents should not be stopped for at least 6 months, if at all.

β2-adrenoceptor agonists
The most widely used bronchodilator preparations contain β2-adrenoceptor agonists that are selective for the respiratory tract and do not stimulate the β1 adrenoceptors of the myocardium. These drugs are potent bronchodilators because they relax the bronchial smooth muscle. Such treatment is very effective in relieving symptoms but does little for the underlying inflammatory nature of the disease.

- Uses

■ Mildest asthmatics with intermittent attacks. Only these people should rely on bronchodilator treatment alone.
Practical Box The stepwise management of asthma
Step PEFR Treatment
1 Occasional symptoms,
less frequent than daily
100% predicted As-required short-acting b2 agonists
If used more than once daily, move to step 2
2 Daily symptoms ≤ 80% predicted Regular inhaled preventer therapy:
Anti-inflammatory drugs: inhaled low-dose corticosteroids up to 800 μg daily.
Leukotriene receptor agonists (LTRA), theophylline and sodium cromoglicate are
less effective
If not controlled, move to step 3
3 Severe symptoms 50–80% predicted Inhaled corticosteroids and long-acting inhaled b2 agonist
Continue inhaled corticosteroid
Add – regular inhaled long-acting β2 agonist (LABA)
Still not controlled, add either LTRA, modified release oral theophylline or β2 agonist
If not controlled, move to Step 4
4 Severe symptoms uncontrolled with highdose inhaled corticosteroids 50–80% predicted High-dose inhaled corticosteroid and regular bronchodilators
Increase high-dose inhaled corticosteroids up to 2000 μg daily
Plus regular long-acting β2 agonists
Plus either LTRA or modified release theophylline or β2 agonist
5 Severe symptoms deteriorating ≤ 50% predicted Regular oral corticosteroids
Add prednisolone 40 mg daily to step 4
6 Severe symptoms deteriorating in spite of prednisolone ≤ 30% predicted Hospital admission
Short-acting bronchodilator treatment taken at any step on an as required basis.
Short-acting β agonists (SABAs) such as salbutamol (100 μg), known as albuterol in the USA, or terbutaline (250 μg) should be prescribed as ‘two puffs as required’. Some patients use nebulizers at home for self-administration of salbutamol or terbutaline. Such treatment is effective, but patients must not rely on repeated home administration of nebulized β2- adrenoceptor agonists for worsening asthma, and must be encouraged to seek medical advice urgently if their condition does not improve. The excessive use of β2 agonists has been linked to the two epidemics of asthma mortality in the 1960s and 1980s.
Practical Box Drugs used in asthma
Short-acting relievers
Inhaled β2 agonists (e.g. salbutamol (albuterol in USA),
terbutaline)
Long-acting relief/disease controllers
Inhaled long-acting β2 agonists (e.g. salmeterol, formoterol)
Inhaled corticosteroids (e.g. beclometasone, budesonide,
fluticasone)
Compound inhaled salmeterol and fluticasone
Sodium cromoglicate
Leukotriene modifiers (e.g. montelukast, zafirlukast, zileuton)
Other agents with bronchodilator activity
Inhaled antimuscarinic agents (e.g. ipratropium, oxitropium)
Theophylline preparations
Oral corticosteroids (e.g. prednisolone 40 mg daily)
Steroid-sparing agents
Methotrexate
Ciclosporin
Intravenous immunoglobulin
Anti-IgE monoclonal antibody – omalizumab
Etanercept
■ SABAs can be taken at any step, as and when required from step 1 to step 6.
■ Poorly controlled asthmatics on standard doses of inhaled steroids. These patients require salmeterol or formoterol, which are highly selective and potent longacting β2-adrenoceptor agonists (LABA) effective by inhalation for up to 12 hours, thereby reducing the need for administration to once or twice daily. Long-acting β2- adrenoceptor agonists improve symptoms and lung function and reduce exacerbations in patients. They should never be used alone but always in combination with an inhaled corticosteroid. Increasingly these drugs are administered as fixed-dose combinations with corticosteroids (salmeterol/fluticasone and formoterol/ budesonide) in the same inhaler (step 3).
β2-adrenoceptor agonists are less effective when given by mouth than when the drug is inhaled, and to help those who cannot coordinate activation of the aerosol and inhalation, several breath-activated or dry powder devices have been developed.

Antimuscarinic bronchodilators
Muscarinic receptors are found in the respiratory tract; large airways contain mainly M3 receptors whereas the peripheral lung tissue contains M3 and M1 receptors. Nonselective muscarinic antagonists – ipratropium bromide (20– 40 μg three or four times daily) or oxitropium bromide (200 μg twice daily) – by aerosol inhalation can be useful during asthma exacerbations, but their overall role in asthma is limited.

Anti-inflammatory drugs
Sodium cromoglicate and nedocromil sodium prevent activation of many inflammatory cells, particularly mast cells, eosinophils and epithelial cells, but not lymphocytes, by blocking a specific chloride channel which in turn prevents calcium influx. These drugs are effective in patients with milder asthma (step 2). Sodium cromoglicate is taken regularly either in the form of a Spincap containing 20 mg or in aerosol form from a metered-dose inhaler delivering 5 mg per puff. The dose should be two puffs four times daily from an inhaler, or one Spincap three or four times daily. Nedocromil sodium is taken as an aerosol at a dose of 4 mg (two puffs) two to four times daily.
Asthma guidelines advise that inhaled corticosteroids are more efficacious than the chromones, but the latter are free of side-effects and, therefore, may offer some advantages in children, especially when there is strong evidence for an allergic component.

Inhaled corticosteroids
All patients who have regular persistent symptoms (even mild symptoms) need regular treatment with inhaled corticosteroids delivered in a stepwise fashion (from step 2 upwards) or as a high dose followed by a reduction to maintenance levels. Beclometasone dipropionate (BDP) is the most widely used inhaled steroid and is available in doses of 50, 100, 200 and 250 μg per puff. Other inhaled steroids include budesonide, fluticasone, mometasone and triamcinolone.
Much of the inhaled dose does not reach the lung but is either swallowed or exhaled. Deposition in the lung varies between 10% and 25% depending on inhaler technique and the technical characteristics of the aerosol device. Drug which is deposited in the airways reaches the systemic circulation directly, through the bronchial circulation, while any drug that is swallowed has to pass through the liver before it can reach the systemic circulation. Gram for gram, fluticasone and mometasone are more potent than beclometasone with considerably less systemic bioavailability, owing to their greater sensitivity to hepatic metabolism. The newer hydrofluoroalkane (HFA) aerosols of beclometasone deliver a higher proportion of useable drug than the old CFC-based aerosols, and the effective dosage of HFA-beclometasone is equivalent to the same dose of HFA-fluticasone, whereas previously the effective dose ratio was 2 : 1. Absorption of beclometasone and budesonide does not seem to present a risk at doses up to 800 μg/day, but when using high-dose inhaled steroids in patients who have not responded to standard doses, fluticasone or mometasone may be preferred because of their lower bioavailability. The dose–response curve for inhaled corticosteroids is flat beyond 800 μg beclometasone or equivalent, and in patients with moderate asthma who are taking this daily, addition of salmeterol or formoterol is more effective than doubling the dose of inhaled corticosteroid.
The unwanted effects of inhaled corticosteroids are oral candidiasis (5% of patients), and hoarseness due to the effect of corticosteroids on the laryngeal muscles. Subcapsular cataract formation is rare but can occur in the elderly. Osteoporosis is a complication when inhaled corticosteroids are taken in high doses (beclometasone or budesonide > 800 μg daily). In children, inhaled corticosteroids at doses greater than 400 μg daily have been shown to retard short-term growth. Inhaled corticosteroid use should be stepped down once asthma comes under control. Candidiasis and GI absorption can be reduced by using spacers, mouthwashing and teeth cleaning after use. More recently inhaled corticosteroids, e.g. ciclesonide 80 μg daily, that are esterified in the lung thereby reducing systemic effects, have become available with a higher therapeutic index.
Asthmatic patients who smoke are less responsive to inhaled corticosteroids, and additional therapy, e.g. with leukotriene receptor antagonists, is required.
Many patients with anything more than mild/moderate asthma benefit from combination LABA/corticosteroid therapy and there is some evidence that the two drugs interact therapeutically. Adding a LABA once the dose of inhaled corticosteroid has reached 800–1000 μg is of proven greater benefit than further increasing the steroid dose.

Oral corticosteroids and steroid-sparing agents
Oral corticosteroids may be necessary for those individuals not controlled on inhaled corticosteroids (step 5). The dose should be kept as low as possible to minimize side-effects. The effect of short-term treatment with prednisolone 30 mg daily. Some patients require continuing treatment with oral corticosteroids. Several studies suggest that treatment with low doses of methotrexate (15 mg weekly) can significantly reduce the dose of prednisolone needed to control the disease in some patients, and ciclosporin also improves lung function in some steroiddependent asthmatics. Several other steroid-sparing strategies including ciclosporin and immunoglobulin have also been tried, but with varying success.

Cysteinyl leukotriene receptor
antagonists (LTRAs)

This class of anti-asthma therapy targets one of the principal asthma mediators by inhibiting the cysteinyl LT1 receptor. A second receptor (cyst LT2) has been identified on inflammatory cells. Montelukast, pranlukast (only available in South East Asia) and zafirlukast are given orally and are effective in a subpopulation of patients. However, it is not possible to predict which individuals will benefit: a 4-week trial of LTRA therapy is recommended before a decision is made to continue or stop. LTRAs should be considered in any patient who is not controlled on low to medium doses of inhaled steroids (step 2). Their action is additive to that of long-acting β2 agonists. LTRAs are particularly useful in patients with aspirin-intolerant asthma, in those patients requiring highdose inhaled or oral corticosteroids and in asthmatic smokers. Because these drugs are orally active they are helpful in asthma combined with rhinitis and in young children with asthma and/or virus associated wheezing.

Monoclonal antibodies
Newer agents that modulate IgE-associated inflammation are being developed. The most promising of these is a recombinant humanized monoclonal antibody that complexes with free IgE – omalizumab – blocking its interaction with mast cells and basophils. Clinical trials in children and adults with severe asthma despite corticosteroids show good efficacy when omalizumab is given subcutaneously once or twice each month depending on total serum IgE level and body weight. Recent proof-of-concept trials have also suggested a place for anti-TNF therapy (blocking monoclonal antibody or soluble receptor fusion protein, etanercept) in corticosteroid refractory severe asthma. There is a need to examine other biologicals as potential new controller therapies for the 5–10% of patients with severe disease, which accounts for a high proportion of the health costs of asthma.

Antibiotics
Although wheezing frequently occurs in infective exacerbations of COPD, there is limited evidence that antibiotics are helpful in the management of patients with asthma. Yellow or green sputum containing eosinophils and bronchial epithelial cells may be coughed up in acute exacerbations of asthma. This is normally due to viral, not bacterial, infection and antibiotics are not required. Occasionally, mycoplasma and Chlamydia infections can cause chronic relapsing asthma and in such cases the use of appropriate antimicrobials is worthwhile if a bacterial diagnosis has been established by culture or serology.

Asthma attack
Although these may occur spontaneously, asthma exacerbations are most commonly caused by lack of treatment adherence, respiratory virus infections associated with the common cold, and exposure to allergen or triggering drug, e.g. an NSAID. Whenever possible patients should have a written personalized plan that they can implement in anticipation of or at the start of an exacerbation that includes the early use of a short course of oral corticosteroids. If the PEFR is greater than 150 L/min, patients may improve dramatically on nebulized therapy and may not require hospital admission. Their regular treatment should be increased, to include treatment for 2 weeks with 30–60 mg of prednisolone followed by substitution by an inhaled corticosteroid preparation. Short courses of oral prednisolone can be stopped abruptly without tailing down the dose.

Acute severe asthma
The term ‘status asthmaticus’ was defined as asthma that had failed to resolve with therapy in 24 hours. Although this term is still used occasionally, it has been mainly discarded and replaced by ‘acute severe asthma’, i.e. severe asthma that has not been controlled by the patient’s use of medication.
Patients with acute severe asthma typically have:
■ inability to complete a sentence in one breath
■ respiratory rate ≥ 25 breaths per minute
■ tachycardia ≥ 110 beats/min (pulsus paradoxus,  is not useful as it is only present in 45% of cases)
■ PEFR < 50% of predicted normal or best. Features of life-threatening attacks are:
■ a silent chest, cyanosis or feeble respiratory effort
■ exhaustion, confusion or coma
■ bradycardia or hypotension
■ PEFR < 30% of predicted normal or best (approximately 150 L/min in adults).
Arterial blood gases should always be measured in asthmatic patients requiring admission to hospital. Pulse oximetry is useful in monitoring oxygen saturation during the admission and reduces the need for repeated arterial puncture. Features suggesting very severe life-threatening attacks are:
■ a high Paco2 > 6 kPa
■ severe hypoxaemia Pao2 < 8 kPa despite treatment with oxygen
■ a low and falling arterial pH.
- Treatment (Emergency box) is commenced with 5 mg of nebulized salbutamol or 10 mg terbutaline with oxygen as the driving gas. Nebulized antimuscarinics (e.g. ipratropium bromide) are also helpful. A chest X-ray is taken to exclude a pneumothorax. If no improvement occurs with nebulized therapy, intravenous infusions of β2-adrenoceptor agonist (salbutamol or terbutaline 250 μg over 10 min) and/or magnesium sulphate (1.2–2 g over 20 min, which also relaxes airways smooth muscle) should be used. Intravenous aminophylline is not given as trials show marginal benefit and side-effects such as nausea and vomiting, cardiac arrhythmia and CNS side-effects are problematic. Hydrocortisone 200 mg i.v. should be administered 4-hourly for 24 hours, and 60 mg of prednisolone should be given orally daily. In patients who do not respond to this regimen, ventilation is often required.
Ideally, patients should be kept in hospital for at least 5 days, since the majority of sudden deaths occur 2–5 days after admission. During this time oxygen saturation should be monitored by oximetry. Oral prednisolone can be reduced from 60 mg to 30 mg once improvement occurs. Further reduction should be gradual on an outpatient basis until an appropriate maintenance dose or substitution by inhaled corticosteroid aerosols can be achieved.
A recent approach for moderate to severe persistent asthma is bronchial thermoplasty. This bronchoscopic procedure reduces the mass of airway smooth muscle, reducing bronchoconstriction, and is being evaluated.
Emergency Box Treatment of severe asthma

At home
1. The patient is assessed. Tachycardia, a high respiratory rate and inability to speak in sentences indicate a severe attack.
2. If the PEFR is less than 150 L/min (in adults), an ambulance should be called. (All doctors should carry peak flow meters.)
3. Nebulized salbutamol 5 mg or terbutaline 10 mg is administered.
4. Hydrocortisone sodium succinate 200 mg i.v. is given.
5. Oxygen 40–60% is given if available.
6. Prednisolone 60 mg is given orally.

At hospital
1. The patient is reassessed.
2. Oxygen 40–60% is given.
3. The PEFR is measured using a low-reading peak flow meter, as an ordinary meter measures only from 60 L/min upwards. Measure O2 saturation with a pulse oximeter.
4. Nebulized salbutamol 5 mg or terbutaline 10 mg is repeated and administered 4-hourly.
5. Add nebulized ipratropium bromide 0.5 mg to nebulized salbutamol/terbutaline.
6. Hydrocortisone 200 mg i.v. is given 4-hourly for 24 hours.
7. Prednisolone is continued at 60 mg orally daily for 2 weeks.
8. Arterial blood gases are measured; if the Paco2 is greater than 7 kPa, ventilation should be considered.
9. A chest X-ray is performed to exclude pneumothorax.
10. One of the following intravenous infusions is given if no improvement is seen:
salbutamol 3–20 μg/min, or
terbutaline 1.5–5.0 μg/min, or
magnesium sulphate 1.2–2 g over 20 min.

Management of catastrophic sudden
severe (brittle) asthma

This is an unusual variant of asthma in which patients are at risk from sudden death in spite of the fact that their asthma may be well controlled between attacks. Severe life-threatening attacks may occur within hours or even minutes. Such patients require a carefully worked out management plan agreed by respiratory physician, primary care physician and patient, and require:
■ emergency supplies of medications at home, in the car and at work
■ oxygen and resuscitation equipment at home and at work
■ nebulized β2-adrenoceptor agonists at home and at work; inhaled long-acting β2-agonists with a corticosteroid can be very effective
■ self-injectable epinephrine (adrenaline): two Epipens of 0.3 mg epinephrine at home, at work and to be carried by the patient at all times
■ prednisolone 60 mg
■ Medic Alert bracelet.
On developing wheeze, the patient should attend the nearest hospital immediately. Direct admission to intensive care may be required.
 
Prognosis of asthma
Although asthma often improves in children as they reach their teens, the disease frequently returns in the second, third and fourth decades. In the past the data indicating a natural decrease in asthma through teenage years have led to childhood asthma being treated as an episodic disorder. However, airway inflammation is present continuously from an early age and usually persists even if the symptoms resolve. Moreover, airways remodelling accelerates the process of decline in lung function over time. This has led to a reappraisal of the treatment strategy for asthma, mandating the early use of controller drugs and environmental measures from the time asthma is first diagnosed.


Asthma : Clinical features - Investigations

Asthma
"Clinical features - Investigations"

Clinical features
The principal symptoms of asthma are wheezing attacks and episodic shortness of breath. Symptoms are usually worst during the night, this being a particularly good marker of uncontrolled disease. Cough is a frequent symptom that sometimes predominates, especially in children in whom nocturnal cough can be a presenting feature. There exists great variation in the frequency and duration of the attacks. Some patients have only one or two attacks a year that last for a few hours, whilst others have attacks lasting for weeks. Some patients have chronic symptoms that persist, on top of which there are fluctuations. Attacks may be precipitated by a wide range of triggers. Asthma is a major cause of impaired quality of life with impact on work and recreational, as well as physical activities, and emotions.

Investigations
There is no single satisfactory diagnostic test for all asthmatic patients.

Lung function tests
Peak expiratory flow rate (PEFR) measurements on waking, prior to taking a bronchodilator and before bed after a bronchodilator, are particularly useful in demonstrating the variable airflow limitation that characterizes the disease. The diurnal variation in PEFR is a good measure of asthma activity and is of help in the longer-term assessment of the patient’s disease and its response to treatment. To assess possible occupational asthma, peak flows need to be measured for at least 2 weeks at work and 2 weeks off work.
Spirometry is useful, especially in assessing reversibility. Asthma can be diagnosed by demonstrating a greater than 15% improvement in FEV1 or PEFR following the inhalation of a bronchodilator. However, this degree of response may not be present if the asthma is in remission or in severe chronic asthma when little reversibility can be demonstrated or if the patient is already being treated with long-acting bronchodilators.
The carbon monoxide (CO) transfer test is normal in asthma.

Exercise tests
These have been widely used in the diagnosis of asthma in children. Ideally, the child should run for 6 minutes on a treadmill at a workload sufficient to increase the heart rate above 160 beats per minute. Alternative methods use cold air challenge, isocapnoeic hyperventilation (forced overbreathing with artificially maintained Paco2) or aerosol challenge with hypertonic solutions. A negative test does not automatically rule out asthma.

Histamine or methacholine bronchial
provocation test

This test indicates the presence of airway hyperresponsiveness, a feature found in most asthmatics, and can be particularly useful in investigating those patients whose main symptom is cough. The test should not be performed on individuals who have poor lung function (FEV1 < 1.5 L) or a history of ‘brittle’ asthma. In children, controlled exercise testing as a measure of BHR is often easier to perform.

Trial of corticosteroids
All patients who present with severe airflow limitation should undergo a formal trial of corticosteroids. Prednisolone 30 mg orally should be given daily for 2 weeks with lung function measured before and immediately after the course. A substantial improvement in FEV1 (> 15%) confirms the presence of a reversible element and indicates that the administration of inhaled steroids will prove beneficial to the patient. If the trial is for 2 weeks or less, the oral corticosteroid can be withdrawn without tailing off the dose, and should be replaced by inhaled corticosteroids in those who have responded.
Exhaled nitric oxide (NO), a measure of airway inflammation and an index of corticosteroid response, is used in children as a test for the efficacy of corticosteroids.

Blood and sputum tests
Patients with asthma may have an increase in the number of eosinophils in peripheral blood (> 0.4 × 109/L). The presence of large numbers of eosinophils in the sputum is a more useful diagnostic tool.

Chest X-ray
There are no diagnostic features of asthma on the chest Xray, although overinflation is characteristic during an acute episode or in chronic severe disease. A chest X-ray may be helpful in excluding a pneumothorax, which can occur as a complication, or in detecting the pulmonary shadows associated with allergic bronchopulmonary aspergillosis.

Skin tests
Skin-prick tests (SPT) should be performed in all cases of asthma to help identify allergic causes. Measurement of allergen-specific IgE in the serum is also helpful if SPT facilities are not available, if the patient is taking antihistamines or if a wide range of allergens are being investigated. Asthma frequently occurs in conjunction with other atopic disorders, especially rhinitis.

Allergen provocation tests
Allergen challenge is not required in the clinical investigation of patients, except in cases of suspected occupational asthma. Another controversial exception is the investigation of food allergy causing asthma. This diagnosis can be difficult, although many patients are concerned about the possibility. In the absence of any obvious allergy, e.g. peanut or milk, if the patient has asthma without any other systemic features, then food allergy is most unlikely to be the cause. Open food challenges are unreliable and if the diagnosis is seriously entertained, blind oral challenges with the food disguised in opaque gelatine capsules are necessary to confirm or refute a causative link. There is much speculation about food intolerance (as opposed to allergy) and asthma including the role of food additives, which occasionally can precipitate severe attacks.

Asthma : Pathogenesis

Asthma
"Pathogenesis"

Pathogenesis
The pathogenesis of asthma is complex and not fully understood. It involves a number of cells, mediators, nerves and
Asthma Treatment Of
Different types of asthmatic reactions following challenge with allergen. M, midnight; N, noon.
vascular leakage that can be activated by several different mechanisms, of which exposure to allergens is among the most significant (Next Fig.). The varying clinical severity and chronicity of asthma is dependent on an interplay between airway inflammation and airway wall remodelling. The inflammatory component is driven by Th2-type T lymphocytes which facilitate IgE synthesis through production of IL-4 and eosinophilic inflammation through IL-5 (Next Fig.). However, as the disease becomes more severe and chronic and loses its sensitivity to corticosteroids, there is greater evidence of a Th1 response with release of mediators such as TNF-α and associated tissue damage, mucous metaplasia and aberrant epithelial and mesenchymal repair.

Inflammation
Several key cells are involved in the inflammatory response that characterizes all types of asthma.
- Mast cells. These are increased in the epithelium, smooth muscle and mucous glands in asthma and release powerful preformed and newly generated mediators that act on smooth muscle, small blood vessels, mucussecreting cells and sensory nerves, such as histamine, tryptase, PGD2 and LTC4, and its metabolites LTD4 and LTE4 (previously known as slow reacting substance of anaphylaxis, SRS-A), which cause the immediate asthmatic reaction. Mast cells are inhibited by such drugs as sodium cromoglicate and β2-agonists which might contribute to their therapeutic efficacy in preventing acute bronchoconstriction triggered by indirect challenges. Mast cells also release an array of cytokines, chemokines and growth factors that contribute to the late asthmatic response and more chronic aspects of asthma.
- Eosinophils. These cells are found in large numbers in the bronchial wall and secretions of asthmatics. They are attracted to the airways by the eosinophilopoietic cytokines IL-3, IL-5 and GM-CSF as well as by chemokines which act on type 3 C-C chemokine receptors (CCR-3) (i.e. eotaxin, RANTES, MCP-1, MCP-3 and MCP-4). These mediators also prime eosinophils for enhanced mediator secretion. When activated, they release LTC4, and basic proteins such as major basic protein (MBP), eosinophil cationic protein (ECP) and peroxidase (EPX) that are toxic to epithelial cells. Both the number and activation of eosinophils are rapidly decreased by corticosteroids. Sputum eosinophilia is of diagnostic help as well as providing a biomarker of response to controller therapy.
- Dendritic cells and lymphocytes. These cells are abundant in the mucous membranes of the airways and the alveoli. Dendritic cells have a role in the initial uptake and presentation of allergens to lymphocytes. T helper lymphocytes (CD4+) show evidence of activation (Next Fig.) and the release of their cytokines plays a key part in the migration and activation of mast cells (IL-3, IL-4, IL-9 and IL-13) and eosinophils (IL-3, IL-5, GM-CSF). In addition, production of IL-4 and IL- 13 helps maintain the proallergic Th2 phenotype, favouring switching of antibody production by B lymphocytes to IgE. In mild/moderate asthma there occurs a selective upregulation of Th2 T cells with reduced evidence of the Th1 phenotype (producing gamma-interferon, TNF-α and IL-2), although additional Th1 prominence may accompany more severe disease. This polarization is mediated by dendritic cells and
Asthma Treatment Of
Inflammatory and remodelling responses in asthma with activation of the epithelial mesenchymal trophic unit. Epithelial damage alters the set point for communication between bronchial epithelium and underlying mesenchymal cells, leading to myofibroblast activation, an increase in mesenchymal volume, and induction of structural changes throughout airway wall. Adapted from Holgate ST, Polosa R. The mechanisms, diagnosis, and management of severe asthma in adults.
involves a combination of antigen presentation, costimulation and exposure to polarizing cytokines. The activity of both macrophages and lymphocytes is influenced by corticosteroids but not β2-adrenoceptor agonists.

Remodelling
A characteristic feature of chronic asthma is an alteration of structure and functions of the formed elements of the airways. Together, these structural changes interact with inflammatory cells and mediators to cause the characteristic features of the disease. Deposition of matrix proteins, swelling and cellular infiltration cause an expansion of the submucosa beneath the epithelium so that for a given degree of smooth muscle shortening there is excess airway narrowing. Swelling outside the smooth muscle layer spreads the retractile forces exerted by the surrounding alveoli over a greater surface area so that the airways close more easily. Several factors contribute to these changes.
- The epithelium. In asthma the epithelium of the conducting airways is stressed and damaged with loss of ciliated columnar cells on to the lumen. Metaplasia occurs with a resultant increase in the number and activity of mucus-secreting goblet cells. The epithelium is a major source of mediators, cytokines and growth factors that serve to enhance inflammation and promote tissue remodelling (previous Fig.). Damage and activation of the epithelium make it more vulnerable to infection by common respiratory viruses, e.g. rhinovirus, coronavirus, and to the effects of air pollutants. Increased production of nitric oxide (NO), due to the increased expression of inducible NO synthase, is a feature of epithelial damage and activation and the measurement of exhaled NO is proving useful as a non-invasive test of continuing inflammation.
- Epithelial basement membrane. A pathognomonic feature of asthma is the deposition of repair collagens (types I, III and V) and proteoglycans in the lamina reticularis beneath the basement membrane. This, along with the deposition of other matrix proteins such as laminin, tenascin and fibronectin, causes the appearance of a thickened basement membrane observed by light microscopy in asthma. This collagen deposition reflects activation of an underlying sheath of fibroblasts that transform into contractile myofibroblasts which also have an increased capacity to secrete matrix. Aberrant signalling between the epithelium and underlying myofibroblasts is thought to be the principal cause of airway wall remodelling, since the cells are prolific producers of a range of tissue growth factors such as epidermal growth factor (EGF), transforming growth factor (TGF) -α and -β, connective tissue-derived growth factor (CTGF), platelet-derived growth factor (PDGF), endothelin (ET), insulin-like growth factors (IGF), nerve growth factors and vascular endothelial growth factors ( previous Fig.). The same interaction between epithelium and mesenchymal tissues is central to branching morphogenesis in the developing fetal lung. It has been suggested that these mechanisms are reactivated in asthma, but instead of causing airway growth and branching, they lead to thickening of the airway wall (remodelling, Previous Fig.). Increased deposition of collagens, proteoglycans and matrix proteins creates a microenvironment conducive to ongoing inflammation since these complex molecules also possess cell-signalling functions, which aid cell movement, prolong inflammatory cell survival and prime them for mediator secretion.
- Smooth muscle. A prominent feature of asthma is hyperplasia of the helical bands of airway smooth muscle. In addition to increasing in amount, the smooth muscle alters in function to contract more easily and stay contracted because of a change in actin–myosin cross-link cycling. These changes allow the asthmatic airways to contract too much and too easily at the least provocation. Asthmatic smooth muscle also secretes a wide range of cytokines, chemokines and growth factors that help sustain the chronic inflammatory response. ADAM33, the newly described asthma gene, may be involved in driving increased airway smooth muscle and other features of remodelling through increased availability of growth factors.
- Nerves. Neural reflexes, both central and peripheral, contribute to the irritability of asthmatic airways. Central reflexes involve stimulation of nerve endings in the epithelium and submucosa with transmission of impulses via the spinal cord and brain back down to the airways where release of acetylcholine from nerve endings stimulates M3 receptors on smooth muscle causing contraction. Local neural reflexes involve antidromic neurotransmission and the release of a variety of neuropeptides. Some of these are smooth muscle contractants (substance P, neurokinin A), some are vasoconstrictors (e.g. calcitonin gene-related peptide, CGRP) and some vasodilators (e.g. neuropeptide Y, vasoactive intestinal polypeptide). The polymorphism in the neuropeptide S receptor (GPR 154) is associated with asthma susceptibility. Bradykinin generated by tissue and serum proteolytic enzymes (including mast cell tryptase and tissue kallikrein) is also a potent stimulus of local neural reflexes involving (nonmyelinated) nerve fibres.

Asthma : Precipitating factors

Asthma
"Precipitating factors"

Precipitating factors
Occupational sensitizers (Next Table)
Over 250 materials encountered at the workplace, accounting for 15% of all asthma cases, give rise to occupational asthma. The causes are recognized occupational diseases in the UK, and patients in insurable employment are therefore

 
Occupational asthma
Cause Source/Occupation
Low molecular weight
(non-IgE related)
 
Isocyanates Polyurethane varnishes
Industrial coatings
Spray painting
Colophony fumes Soldering/welders
Electronics industry
Wood dust
Drugs
Bleaches and dyes
Complex metal salts, e.g.
nickel, platinum,
chromium
High molecular weight
(IgE related)
 
Allergens from animals
and insects
Farmers, workers in poultry and
seafood processing industry;
laboratory workers
Antidotes Nurses, health industry
Latex Health workers
Proteolytic enzymes Manufacture (but not use) of
‘biological’ washing powders
Complex salts of platinum Metal refining
Acid anhydrides and
polyamine hardening
agents
Industrial coatings

eligible for statutory compensation provided they apply within 10 years of leaving the occupation in which the asthma developed.
Asthma can be due to:
■ high molecular weight compounds, e.g. flour, organic dusts and other large protein molecules involving specific IgE antibodies, or
■ low molecular weight compounds, e.g. reactive chemicals such as isocyanates and acid anhydrides that bond chemically to epithelial cells to activate them as well as provide haptens recognized by T cells.

The risk of developing some forms of occupational asthma increases in smokers. The proportion of employees developing occupational asthma depends primarily upon the level of exposure. Proper enclosure of industrial processes or appropriate ventilation greatly reduces the risk. Atopic individuals develop occupational asthma more rapidly when exposed to agents causing the development of specific IgE antibody. Non-atopic individuals can also develop asthma when exposed to such agents, but after a longer period of exposure.

Non-specific factors
The characteristic feature of BHR in asthma means that, as well as reacting to specific antigens, the airways will also respond to a wide variety of non-specific direct and indirect stimuli.

Cold air and exercise
Most asthmatics wheeze after prolonged exercise. Typically, the attack does not occur while exercising but afterwards. The inhalation of cold, dry air will also precipitate an attack. Exercise-induced wheeze is driven by release of histamine, prostaglandins (PGs) and leukotrienes (LTs) from mast cells as well as stimulation of neural reflexes when the epithelial lining fluid of the bronchi becomes hyperosmolar owing to drying and cooling during exercise. The phenomenon can be shown by exercise, cold air and hypertonic (e.g. saline or mannitol) provocation tests.

Atmospheric pollution and irritant dusts,
vapours and fumes

Many patients with asthma experience worsening of symptoms on contact with tobacco smoke, car exhaust fumes, solvents, strong perfumes or high concentrations of dust in the atmosphere. Major epidemics have been recorded when large amounts of allergens are released into the air, e.g. soybean epidemic in Barcelona. Asthma exacerbations increase in both summer and winter air pollution episodes associated with climatic temperature inversions. Epidemics of the disease have occurred in the presence of high concentrations of ozone, particulates and NO2 in the summer and particulates, NO2 and SO2 in the winter.

Diet
Increased intakes of fresh fruit and vegetables have been shown to be protective, possibly owing to the increased intake of antioxidants or other protective molecules such as flavonoids. Genetic variation in antioxidant enzymes is associated with more severe asthma.

Emotion
It is well known that emotional factors may influence asthma both acutely and chronically, but there is no evidence that patients with the disease are any more psychologically disturbed than their non-asthmatic peers. An asthma attack is a frightening experience, especially when of sudden and unexpected onset. Patients at special risk of life-threatening attacks are understandably anxious.

Drugs
- Non-steroid anti-inflammatory drugs (NSAIDs). NSAIDs, particularly aspirin and propionic acid derivatives, e.g. indometacin and ibuprofen, have a role in the development and precipitation of asthma in approximately 5% of patients. NSAID intolerance is especially prevalent in those with both nasal polyps and asthma and is not infrequently associated with a triad of asthma, rhinitis and flushing on drug exposure. In susceptible subjects exposure to NSAIDs reveals an imbalance in the metabolism of arachidonic acid. NSAIDs inhibit arachidonic acid metabolism via the cyclo-oxygenase (COX) pathway, preventing the synthesis of certain prostaglandins. In aspirin-intolerant asthma there is reduced production of PGE2 which, in a sub-proportion of genetically susceptible subjects, induces the overproduction of cysteinyl leukotrienes by eosinophils, mast cells and macrophages. In such patients there is evidence for genetic polymorphisms involving the enzymes and receptors of the leukotriene generating pathway (Next Fig.). Interestingly, asthma in intolerant patients is not precipitated by COX-2 inhibitors, indicating that it is blockade of the COX-1 isoenzyme that is linked to impaired PGE2 production.
- Beta-blockers. The airways have a direct parasympathetic innervation that tends to produce bronchoconstriction. There
Asthma Treatment Of
Arachidonic acid metabolism and the effect of drugs. The sites of action of NSAIDs (e.g. aspirin, ibuprofen) are shown. The enzyme cyclo-oxygenase occurs in three isoforms, COX-1 (constitutive), COX-2 (inducible) and COX-3 (in brain). PG, prostaglandin; BLT, B leukotriene receptor; cysLT, cysteinyl leukotriene receptor.
is no direct sympathetic innervation of the smooth muscle of the bronchi, and antagonism of parasympathetically induced bronchoconstriction is critically dependent upon circulating epinephrine (adrenaline) acting through β2-receptors on the surface of smooth muscle cells. Inhibition of this effect by β-adrenoceptor-blocking drugs such as propranolol leads to bronchoconstriction and airflow limitation, but only in asthmatic subjects. The so-called selective β1-adrenergicblocking drugs such as atenolol may still induce attacks of asthma; their use to treat hypertension or angina in asthmatic patients is best avoided.

Allergen-induced asthma
The experimental inhalation of allergen by atopic asthmatic individuals leads to the development of different types of reaction, as illustrated in next Figure.
- Immediate asthma (early reaction). Airflow limitation begins within minutes of contact with the allergen, reaches its maximum in 15–20 minutes and subsides by 1 hour.
- Dual and late-phase reactions. Following an immediate reaction many asthmatics develop a more prolonged and sustained attack of airflow limitation that responds less well to inhalation of bronchodilator drugs such as salbutamol. Isolated late-phase reactions with no preceding immediate response can occur after the inhalation of some occupational sensitizers such as isocyanates. During and up to several weeks after the exposure, the airways are hyperresponsive, which may explain persisting symptoms after allergen exposure.

Asthma : Introduction - Prevalence - Classification - Aetiology and pathogenesis

Asthma
"Introduction - Prevalence - Classification - Aetiology and pathogenesis"

Asthma is a common chronic inflammatory condition of the lung airways whose cause is incompletely understood. Symptoms are cough, wheeze, chest tightness and shortness of breath, often worse at night. The most frequent form has its onset in childhood between the ages of 3 and 5 years and may either worsen or improve during adolescence. Classically asthma has three characteristics:
■ airflow limitation which is usually reversible spontaneously or with treatment
■ airway hyperresponsiveness to a wide range of stimuli (see below)
■ inflammation of the bronchi with T lymphocytes, mast cells, eosinophils with associated plasma exudation, oedema, smooth muscle hypertrophy, matrix deposition, mucus plugging and epithelial damage.
In chronic asthma, inflammation may be accompanied by irreversible airflow limitation as a result of airway wall remodelling that may involve large and small airways and mucus impaction.

Prevalence
In many countries the prevalence of asthma is increasing. This increase, with its accompanying allergy, is particularly in children and young adults where this disease may affect up to 15% of the population. There is also a geographical variation, with asthma being commoner in more developed countries. Some of the highest rates are in the UK, New Zealand and Australia, but the rates are lower in Far Eastern countries such as China and Malaysia, Africa and Central and Eastern Europe. However, long-term follow-up in developing countries suggests that the disease may become more frequent as individuals adopt a more ‘westernized’ lifestyle, but the environmental factors accounting for this remain unknown. Studies of occupational asthma suggest that a high percentage of the workforce, 15–20%, may become asthmatic if exposed to potent sensitizers. World-wide, approximately 300 million people have asthma and this is expected to rise to 400 million by 2025.

Classification
Asthma is a complex disorder of the conducting airways that most simply can be classified as:
■ extrinsic – implying a definite external cause
■ intrinsic – when no causative agent can be identified.
Extrinsic asthma occurs most frequently in atopic individuals who show positive skin-prick reactions to common inhalant allergens such as dust mite, animal danders, pollens and fungi. Positive skin-prick tests to inhalant allergens are shown in 90% of children and 70% of adults with persistent asthma. Childhood asthma is often accompanied by eczema (atopic dermatitis). A frequently overlooked cause of late-onset asthma in adults is sensitization to chemicals or biological products in the workplace.
Intrinsic asthma often starts in middle age (‘late onset’). Nevertheless, many patients with adult-onset asthma show positive allergen skin tests and on close questioning give a history of respiratory symptoms compatible with childhood asthma.
Non-atopic individuals may develop asthma in middle age from extrinsic causes such as sensitization to occupational agents such as toluene diisocyanate, intolerance to nonsteroidal anti-inflammatory drugs such as aspirin or because they were given β-adrenoceptor-blocking agents for concurrent hypertension or angina that block the protective effect of endogenous adrenergic agonists. Extrinsic causes must be considered in all cases of asthma and, where possible, avoided.

Aetiology and pathogenesis
The two major factors involved in the development of asthma and many other stimuli that can precipitate attacks are shown in next figure.

Atopy and allergy
The term ‘atopy’ was used by clinicians at the beginning of the twentieth century to describe a group of disorders, including asthma and hayfever, that appeared:

 
Asthma Treatment Of
Causes and triggers of asthma. RSV, respiratory syncytial virus; NSAIDs, non-steroidal antiinflammatory drugs.


■ to run in families
■ to have characteristic wealing skin reactions to common allergens in the environment
■ to have circulating allergen-specific IgE.
Allergen-specific IgE is present in 30–40% of the UK population, and there is a link between serum IgE levels and both the prevalence of asthma and airway hyperresponsiveness. Genetic and environmental factors affect serum IgE levels.

Genetic

Genes, in combination with environmental factors, may turn out to play a key role in the development of asthma.
■ Genes controlling the production of the cytokines IL-3, IL-4, IL-5, IL-9, IL-13 and GM-CSF – which in turn affect mast and eosinophil cell development and longevity as well as IgE production – are present in a cluster on chromosome 5q31–33 (the IL-4 gene cluster).
■ Polymorphic variation in proteins along the IL-4/-13 signalling pathway is strongly associated with allergy and asthma.
■ Novel asthma genes identified by positional cloning from whole genome scans are the PHF11 locus on chromosome 2 (that includes genes SETDB2 and RCBTB1) and transcription factors, which are implicated in IgE synthesis and associated more with atopy than asthma.
■ ADAM 33 (a disintegrin and metalloproteinase) on chromosome 20p13 is more strongly associated with airway hyperresponsiveness and tissue remodelling.
■ Other recently discovered genes associated with asthma are those that encode neuropeptide S receptor (GPRA or GPR154) on chromosome 7p15, HLA-G on chromosome 6p21, dipeptidyl peptidase 10 on chromosome 2q14 and most recently on chromosome 17q21 ORMDL3, a member of a gene family that encodes transmembrane proteins anchored in the endoplasmic reticulum.

Environmental factors
Early childhood exposure to allergens and maternal smoking has a major influence on IgE production. Much current interest focuses on the role of intestinal bacteria and childhood infections in shaping the immune system in early life. It has been suggested that growing up in a relatively ‘clean’ environment may predispose towards an IgE response to allergens (the ‘hygiene hypothesis’). Conversely, growing up in a ‘dirtier’ environment may allow the immune system to avoid developing allergic responses. Components of bacteria (e.g. lipopolysaccharide endotoxin; immunostimulatory CpG DNA sequences; flagellin), viruses (e.g. SS- and DS-RNA) and fungi (e.g. chiton, a cell wall component) are able to stimulate up to 10 different toll-like receptors (TLRs) expressed on immune and epithelial cells to direct the immune and inflammatory response away from the allergic (Th2) towards protective (Th1 and Treg) pathways. Th1 immunity is associated with antimicrobial protective immunity whereas regulatory T cells are strongly implicated in tolerance to allergens. Thus early life exposure to inhaled and ingested products of microorganisms, as occurs in livestock farming communities and developing countries, may be critical in helping shape the subsequent risk of a child becoming allergic and/or developing asthma.
The allergens involved in asthma are similar to those in rhinitis although pollen exposure causes hay fever to a greater extent than asthma. Allergens from the faecal particles of the house-dust mite are associated with most cases of asthma world-wide. Cockroach allergy has been implicated in asthma in US inner-city children, while allergens from furry pets (especially cats) are increasingly common causes. The fungal spores from Aspergillus fumigatus give rise to a complex series of lung disorders, including asthma. Many allergens, including those from Aspergillus, have intrinsic biological properties, e.g. proteolytic enzymes that facilitate their passage through the airway epithelium to increase their sensitizing capacity.
Chitins are cross-linked polysaccharides found in the exoskeleton of insects and cockroaches, fungi and in the eggs of helminths. They can be inhaled into the airways. Chitinase-family proteins may play a role in the pathogenesis of asthma as the levels in the lungs and the serum are high in asthma and correlate with disease activity.

Increased responsiveness of the airways of
the lung (airway hyperresponsiveness)

Bronchial hyperresponsiveness (BHR) is demonstrated by asking the patient to inhale gradually increasing concentrations of either histamine or methacholine (bronchial provocation tests). This induces transient airflow limitation in susceptible individuals (approximately 20% of the population); the dose of the agonist (provocation dose, PD) necessary to produce a 20% fall in FEV1 is known as the PD20 FEV1 (or provocation concentration PC20 FEV1). Patients with clinical symptoms of asthma respond to very low doses of methacholine, i.e. they have a low PD20 FEV1 (< 11 μmol). Exercise testing or inhalation of cold dry air, mannitol or hypertonic saline are other methods to assess BHR, but all of these involve the stimulus first releasing endogenous mediators such as histamine, prostaglandins and leukotrienes into the airways to cause the bronchoconstriction (indirect BHR). Measures of indirect BHR correlate more closely with symptoms and diurnal peak expiratory flow rate (PEFR) variation than PC20 histamine or methacholine and both are useful in diagnosing asthma if there is doubt and in guiding controller treatment.
Some patients also react to methacholine but at higher doses and include those with:
■ attacks of asthma only on extreme exertion, e.g. winter sports enthusiasts
■ wheezing or prolonged periods of coughing following a viral infection
■ seasonal wheeze during the pollen season
■ allergic rhinitis, but not complaining of any lower respiratory symptoms until specifically questioned
■ some subjects with no respiratory symptoms.
Although the degree of hyperresponsiveness can itself be influenced by allergic mechanisms, its pathogenesis and mode of inheritance involve a combination of airway inflammation and tissue remodelling.

Asthma Index

Asthma Index


Introduction - Prevalence - Classification - Aetiology and pathogenesis.
Precipitating factors.
Pathogenesis.
Clinical features - Investigations.
Management - Management of catastrophic sudden severe (brittle) asthma - Prognosis.

Respiratory Images

- Asthma





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