Pitfalls in the diagnosis of asthma.

Asthma is a common disease which affects at least 2% of the British population (Gregg, 1977). The last two decades have seen major advances in safe treatment with regular inhalation of sodium cromoglycate, selective beta2 stimulant drugs (salbutamol, terbutaline etc.) or beclomethasone. For the majority of asthmatics, these drugs can achieve excellent control and allow the patient to lead a normal life even if treatment with oral corticosteroids is also required. It is therefore depressing to note that there is, as yet, little evidence of a significant improvement in asthma mortality. A recent survey (British Thoracic Association, 1982) reported a mortality rate of 1-84 per 100,000, which indicates no real improvement on rates of 0A46-1-34 per 100,000 reported over the last century by Speizer and Doll (1968). Several recent studies of asthma mortality (Cochrane and Clark, 1975; Ormerod and Stableforth, 1980; British Thoracic Association, 1982) have highlighted two consistent problems; failure to diagnose and assess the severity of asthma by using simple respiratory function tests and, as a result, failure to implement adequate treatment. In this article, I would like to remind the reader of some of the more important pitfalls in the diagnosis of asthma. Asthma can mimic other respiratory or even cardiac diseases and a common failing is to omit it from the differential diagnosis in patients who do not have the classical and commonest presentation with childhood onset associated with wheezing on exposure to common inhaled allergens such as house dust and grass pollen. Many children are therefore misdiagnosed as having repeated 'bronchitis' and are treated ineffectively with repeated courses of antibiotics when the problem is asthma provoked by viral infections of the bronchial tree. Children, in particular, may appear only to cough, rather than wheeze, and this most commonly occurs at night. The diagnosis may be confirmed by observing wheezing repeatedly when the child is examined or, ideally, by demonstrating variable airflow obstruction by monitoring peak expiratory flow rate (PEFR). If the diagnosis remains in doubt, however, a trial of regular bronchodilator therapy is mandatory. This is a safe investigation, particularly if aerosol drugs are used, but the undiagnosed, untreated asthmatic child is always at risk. While 'wheezy bronchitis' may be much commoner than true asthma, most children with recurrent attacks do turn out to have true asthma and this should be suspected sooner rather than later. Similarly, in the older age groups, late onset intrinsic asthma may be missed. Particularly if patients have smoked (and smoking is much commoner in asthmatics than one might expect), a diagnosis of chronic bronchitis will be made and treatment limited to advice to stop smoking and courses of antibiotics. These patients will then be sentenced to years of misery from their airways obstruction which, at least in the earlier stages, may be quite amenable to treatment. Sputum production can be quite profuse in asthma and may satisfy the criteria for chronic bronchitis. It is therefore a good policy to give serious consideration to a careful trial of regular treatment with aerosol beta2 stimulants, anticholinergic drugs and subsequently oral steroids in any patient with chronic airways obstruction if there is no documented evidence that they have previously been shown to have no reversibility after such treatment. In patients with asthma, or an asthmatic component to their airways obstruction, a response to corticosteroids is usually seen after about 8 days (Webb, Clark and Chilver, 1981). There has recently been a considerable interest in the phenomenom of nocturnal or early morning asthma (Editorial, 1981a). This apparently relates to a normal circadian rhythm in airway calibre which is exaggerated by the asthmatic's labile airways. Nocturnal cough and wheezing should alert the clinician to the diagnosis of asthma and it has long been known that asthma attacks can occur almost exclusively at night in some patients (Floyer, 1698). It is