Special forms of asthma
In many cases, the cause of asthma is unknown. In others, however, an allergen will commonly trigger an attack. Other special forms of asthma include nocturnal asthma, aspirin-sensitive asthma and brittle asthma.
Allergic asthma
If an allergy or more than one allergy has been identified as being potentially important on the basis of your history, it is sometimes necessary to do further tests to confirm this and to identify the allergen. The test is simple and takes about half an hour to complete.
A series of drops of various solutions of substances, which are known to cause allergic reactions (for example, house dust mite, grass pollen, tree pollen, cat dander, etc.), are placed on the forearm. Using small needle points, the skin surface is then gently pierced through each droplet to allow the substance to get under the skin. After 15 minutes or so, local reactions can occur, which look like small areas of nettle rash and usually itch. The needle pricks themselves are not painful – just a tiny scratch – but the itching can be maddening and lasts half an hour or so.
The size of the reaction (or weal) can be measured for each allergen, which gives an idea, not only of what you are allergic to, but also of how allergic you may be to each allergen. Sometimes this is helpful in management because it could tell you which triggers to avoid and could identify things that may turn out to be not so important.
The danger is that small reactions may not be important but sometimes, as a result, patients will then take unnecessary actions. I have seen the occasional patient on extraordinary and unnecessary diets, based on weakly positive skin tests, which have not helped their asthma. This is not always the case: everyone is an individual and his or her needs must be individually addressed.
Desensitisation
If you are shown to be allergic to a particular allergen (for example, cat or rabbit), you can’t avoid contact with these animals and your asthma continues to be poorly controlled by the usual treatment regimens, desensitisation may be considered. This should be done only at specialist centres and should be undertaken only for one allergen at a time. Certainly, for patients with asthma, they should be conducted only at a hospital because there have been many examples of severe reactions to desensitisation, with attacks of asthma needing hospital admission and even causing deaths. For hay fever alone the dangers are less, but for asthma great care needs to be taken.
The process involves a series of injections of small amounts of the substance to which you are allergic, usually under the skin of the upper arm. Very, very small quantities are used to start with, the concentrations increasing week by week or day by day (‘rush’ immunotherapy) to avoid severe allergic reactions. There are different timescales over which the courses of injections are undertaken before a course is considered complete, and this will be up to the centre involved and your needs. Small local reactions (a reddening of the skin at the injection site) are not infrequent, but these settle quickly on the day of the injection. Once the course is complete, boosters can be given at varying intervals if the course has been thought to be successful.
In the UK, desensitisation for asthma is only rarely undertaken, largely because of the fear of bad reactions, but also because many doctors do not believe that this treatment works. If you wish to talk further about whether this might be of use (and it is likely to be useful in only a minority of patients with asthma), then ask your GP for a referral to a centre with experience in this area. A list of specialist centres can be obtained from Allergy UK (see ‘Useful addresses’).
Nocturnal asthma
Night-time asthma is often regarded as a particular type of asthma. In fact, waking at night with asthma is an indication of asthma that is poorly controlled overall and applies to any patient with any type of asthma. In most cases, appropriate treatment will overcome the problem but some patients are more difficult to control. In these patients, factors such as acid reflux (stomach acid coming back into the chest at night and causing irritation) may be a cause and need treatment. Some drugs, such as theophyllines and the long-acting inhaled bronchodilators, are often helpful in controlling symptoms of nocturnal asthma.
Aspirin-sensitive asthma
Aspirin sensitivity occurs in around five per cent of adult patients with asthma. It is very rare in children. These patients are nearly always negative on skin testing for allergens and may suffer from nasal polyps on a recurring basis. If you are such a patient, you must avoid all aspirin-containing drugs, including a wide range of arthritis drugs such as ibuprofen, diclofenac and indometacin (collectively the non-steroidal anti-inflammatory drugs or NSAIDs). If you are unsure whether a particular drug might interfere with your asthma, ask your GP or your pharmacist. Patients with aspirin-sensitive asthma can die from unwittingly swallowing a preparation containing aspirin. Although the treatment usually simply involves avoidance, desensitisation can be done with success, but this is available only in specialist centres.
Desensitisation for this form of asthma is done using small doses of aspirin given orally, the patient being closely monitored at hospital with repeated breathing tests for some hours after each dose. It is time-consuming in the first instance, but is worthwhile for some.
Brittle asthma
Brittle asthma is a rare form of asthma. The patient suffers from sudden severe attacks, sometimes in spite of apparently being very well controlled. Others develop attacks on a background of asthma, which doctor and patient have great difficulty in controlling on a day-to-day basis. These patients keep being admitted to hospital and are at increased risk of dying from their asthma. Allergy seems to be more common in these patients and sometimes their acute attacks follow inhaling or eating something to which they are allergic. Their asthma often puts a huge strain on both the patient and family, and psychological factors seem to be very important – but whether the asthma causes the psychological disturbance or the other way around is a moot point.
Treatment is extremely difficult and patients should be managed by chest specialists with an interest in the more severe forms of asthma.
