Patients suffering from asthma exhibit virtually identical symptoms to those suffering from airflow limitation caused by chronic bronchitis and emphysema. Wheezing attacks and episodic shortness of breath are almost universal. Symptoms are usually worst during the night. Cough is a frequent symptom that sometimes predominates and is often misdiagnosed as being due to bronchitis. Nocturnal cough can be a presenting feature. There is a tremendous variation in the frequency and duration of the attacks. Some patients may have only one or two attacks a year that last for a few hours, whilst others may have attacks lasting for weeks. Some patients can have chronic symptoms. Attacks may be precipitated by all the factors illustrated; the signs of asthma are listed.
There is no single satisfactory diagnostic test for all asthmatic patients.
Lung function tests
The diagnosis of asthma is based on the demonstration of a greater than 15% improvement in FEYl or PEFR following the inhalation of a bronchodilator. However, this is often not present if the asthma is in remission or in very severe chronic disease, when little reversibility can be demonstrated.
Peak flow charts
Measurements of PEFR on waking, in the middle of the day, and before bed are particularly useful in demonstrating the variable airflow limitation that characterizes the disease. An example is shown. This technique is also of help in the longer-term assessment of the patient’s disease and its response to treatment. Peak flows need to be measured over several days and preferably over a weekend or short holiday if the effect of work exposure is also being studied.
These have been widely used in the diagnosis of asthma in children. Ideally, the child should run for 6 min on a treadmill at a work-load sufficient to increase the heart rate above 160 beats per minute. A negative test does not rule out asthma.
Histamine or methacholine bronchial provocation tests
This test indicates the presence of airway hyperreactivity, a feature found in all 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 (FEV\ <1.5Iitres).
Trial of corticosteroids
Prednisolone 30 mg orally should be given daily for 2 weeks to all patients who present with severe airflow limitation. A substantial improvement (> 15%) confirms the presence of an asthmatic element and that the administration of steroids will prove beneficial to the patient. The dose is slowly reduced over several weeks and is replaced by inhaled corticosteroids in those who will benefit. Blood and sputum tests Patients with asthma may have an increase in the number of eosinophils in peripheral blood (>0.4 x 1Q9/litre). This is rarely helpful in the diagnosis. The presence of large numbers of eosinophils, particularly when present in clumps in sputum, is helpful in the differential diagnosis of asthma from chronic bronchitis and emphysema.
There are no diagnostic features of asthma on the chest X-ray. 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 should be performed in all cases of asthma to help identify extrinsic causes. Experimentally, the inhalation of an allergen that gives rise to a large weal on skin testing will almost always produce an attack of asthma in patients with the disease, but whether this occurs in everyday life depends on the concentrations encountered in the atmosphere.
Allergen provocation tests
These are seldom, if ever, required in the clinical investigation of patients. An exception is the investigation of food allergy causing asthma. This diagnosis is difficult; blind oral challenges with the food disguised in opaque gelatine capsules are necessary to confirm or refute a causative link