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.
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.
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.
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