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What you need to know about allergy

Allergy consultant Dr Alaisdair Stewart answers Dr Linden Ruckert‘s questions on the hygiene hypothesis, choosing an antihistamine and RAST testing

Allergy consultant Dr Alaisdair Stewart answers Dr Linden Ruckert‘s questions on the hygiene hypothesis, choosing an antihistamine and RAST testing

1. The prevalence of allergy does seem to be increasing – including onset in small children and older people. I've read that the hygiene hypothesis is now less favoured. Do we have any idea why there is so much allergy?

41229502The prevalence of allergic disease has more than tripled over the past 25 years for many reasons. Improved disease recognition – or the fact that patients now report disease that they previously managed themselves – only accounts for a part of it.

The cause is multifactorial. The hygiene hypothesis is still an important explanation for much of the increase but not the only one.

In utero and when we are born we all have an immune system that tends to react to new allergens with a T Helper 2 lymphocyte (TH2) type response which includes IgE production.

In early life, exposure to infection and super-antigens switch our immune reaction over to a more ‘normal' TH1 response that protects us from infection through IgG and killer cells.

In individuals genetically predisposed to allergy, our increasingly hygienic world impairs this switchover – so increasing the chances of developing allergic diseases.

Modern living also increases our exposure to highly allergenic peptides such as cat saliva, dust mites and foods such as peanuts at a young age, further enhancing the risk of allergic disease.

Changes in our diets and lifestyles – reduced vitamins, selenium, manganese, zinc and antioxidants, and increased exposure to saturated fats, colourings, preservatives, salt and cigarettes – further compound the problem.

Urbanisation thus increases our exposure to allergens while removing many of the protective mechanisms of the past.

Having said that, I think most people would opt for allergic diseases over the infant mortality from infections seen in the past.

2. Is there much difference in the various eye drops available for allergic conjunctivitis? Do you have any tips for hard-to-control eye problems?

Most people with allergic conjunctivitis will also have allergic rhinitis – eye symptoms on their own are unusual. The history may suggest the allergen and – if proven by skin prick testing or blood specific IgE testing (RAST) – then attempts at allergen avoidance may help.

Antihistamine tablets such as desloratidine may help and once-daily nasal steroids such as fluticasone (Avamys) can improve both nose and eye symptoms in those with rhino-conjunctivitis.

If eye drops are needed I find olopatadine twice-daily effective as a topical antihistamine. Nedocromil or sodium cromoglycate eye drops have other anti-inflammatory properties but need to be used four times a day. The fewer the number of applications the greater the compliance.

Unfortunately all of the eye drops contain preservative, which can sting. It's worth patients trying several to find one that works.

Montelukast is effective in allergic rhino-conjunctivitis but doesn't have a licence for this in the UK.

In those individuals with severe proven hay fever, desensitisation with Grazax greatly improves eye symptoms.

3. Is there really much difference in the non-sedative antihistamines? Does tachyphylaxis occur? Is there any benefit in changing from one to another?

They all work through similar mechanisms and each manufacturer finds reasons to favour their products.

Patients vary in how well they respond to certain medications both in terms of benefit and side-effect profile and that includes the degree of sedation.

So again it's worthwhile trying a few to find the medication that best suits.

Once-daily treatment improves compliance – few people remember to take tablets three times a day – and for chlorpheniramine a whole day's cover requires a qds prescription and unacceptable sedation.

There's little to choose between the drugs. I favour desloratadine as it is the only one that doesn't have alcohol consumption as a contraindication. After all, many people want their rhinitis treated so they can enjoy life more, particularly on warm summer barbecue evenings.

Many patients report tachyphylaxis, although the scientific evidence is weak. Treat the patient and change the medication if the patient has lost confidence in its effects.

Remember in allergy there is a strong placebo effect, so positive action in itself can reap benefits.

4. Who should be considered for desensitising treatment? Has the grass pollen treatment been shown to be useful? How many UK centres provide this?

Recently developed, clean, standardised mono-allergen vaccines and sublingual preparations have been shown to be both safe and efficacious in patients who have failed on standard therapy with improvement in symptoms (eyes, nose and asthma) by up to 50% and reduced need for rescue treatment.

In the case of injection therapy, benefit is still present six years after completing treatment.

But treatment is costly and currently should be reserved for those with grass pollen allergy proven by skin-prick testing and intolerable life-altering symptoms despite maximal therapy – with antihistamines, nasal steroids started pre-season, eye drops and possibly montelukast.

Finally, there should be no other significant symptom-causing allergens that cannot be avoided.

People who meet these criteria should be referred to a specialist service. They will determine whether hospital-based injection therapy or community-based sublingual therapy is indicated. In the UK there are a growing number of centres that can perform this assessment. Choose and Book will identify your local service.

Sublingual therapy with Grazax is much easier but because of the cost and high prevalence of hay fever (13% of the population) PCTs will often have protocols to ensure that only the most needy receive the therapy.

5. I have a number of patients who have tried most nasal sprays and even nebules for rhinitis. What else can we do to help them?

First, confirm the key symptoms, check the diagnosis and consider its cause and treat that. Not all rhinitis is due to allergy. Atrophic rhinitis may be best treated by saline douches, vasomotor rhinitis with much rhinorrhoea responds best to ipratropium (Rinatec).

Consider the many possible endocrine and connective tissue disorder causes. Also consider if gastro-oesophageal reflux is the cause, particularly if associated with chronic rhino-sinusitis.

Consider whether there are aspirin-induced nasal polyps and a history to suggest aspirin sensitivity. If so, consider desensitisation or salicylate in food reduction or even montelukast.

If it's an allergy, confirm the cause and where possible suggest the patient avoid it. If that's not possible make sure the patient starts once-daily nasal steroid a week or so before the season starts and continues it daily as a preventer until the end of the season – dependent on the patient's allergen profile.

Nasal antihistamines such as azelastine may be worth a try too. Nasal decongestants should be avoided as they can cause chronic rhinitis.

Montelukast in the UK only has a licence to treat allergic rhinitis in those people with asthma on an inhaled steroid. But, as mentioned above, it can be very effective in other cases of allergic rhinitis and is certainly worth a try off-licence if a person is severely afflicted.

Remember allergic rhinitis commonly precedes asthma – most people with asthma will have allergic rhinitis and they often have a more difficult to control asthma. There is a lot of evidence to suggest that treating the nose greatly improves asthma control – an aspect of management that is often neglected.

Further advice can be found in the ARIA guidelines found at www.whiar.org

6. Many patients report some facial swelling or itching of the throat after certain foods. Is it possible to be clear about who does and does not need an Epipen?

This is a complex area and each case needs to be decided on its own merit. The history and the timing of onset of the reaction is important. Food reactions occur within minutes of ingestion. Those events occurring more than two hours after the food are not due to allergy.

The quicker the onset of reaction and the more severe the past reactions, the greater the need for an Epipen.

Oral allergy syndrome is a common, local reaction in the mouth to various fruits, tree nuts and peanuts which occurs on the background of a pollen rhino-conjunctivitis. This is unlikely to require an Epipen, as the symptoms are relatively trivial and the food can be avoided.

Likewise, most cases of chronic idiopathic urticaria and angioedema are not due to allergy and adrenaline is rarely required.

People with early systemic reactions – that is reactions away from the contact site – will require access to adrenaline unless the cause can easily be avoided, such as drug allergy.

I would have a lower threshold to prescribe in difficult to control asthma, in children, where avoidance is more difficult and in situations where there is inadequate healthcare or access or there are language difficulties.

7. How likely is it that a child will grow out of, say, a peanut allergy?

While there are reports of children growing out of peanut allergy this is generally not the case, particularly in those who have had a moderate or severe systemic reaction. My experience is that it's a lifelong condition.

Oral allergy syndrome may wax and wane and tolerance is possible as is shown by the recent success in improving tolerance in peanut-allergic children.

More information on this will become available in the next few years and local allergy centres will be able to advise.

8. The whole issue of food allergy – outside of anaphylaxis – and sensitivity is very difficult as many patients are convinced there is a link, especially with eczema. Has there been any change in opinion on this?

In all allergic disease the history is of paramount importance to identify associations and determine severity.

Eczema is different from food anaphylaxis. Eczema is a word that includes many causes of skin rashes. To me it means ‘atopic dermatitis', which as its name implies is a rash that occurs in people with an atopic tendency.

Atopy describes the production of IgE in response to a variety of proteins. It does not mean that such sensitivity will cause disease. Hence measuring IgE or specific IgE is rarely helpful. The raised values are usually due to the disease rather than its cause.

If a food is important then the history will raise that as a possible cause. But as eczema is a cell-mediated disease, the worsening of symptoms will often occur 24 hours after increased exposure.

As most children grow out of food allergies and atopic dermatitis between the ages of three and five, the effects of dietary exclusion have to be weighed against the benefits.

9. Is it ever useful to do RAST tests in general practice?

RAST tests for a specific IgE are available to GPs but they're not as useful, specific, sensitive or cheap as skin-prick tests. They are easy to order but require you to have a clear idea of the likely allergen. A degree of specialist knowledge is required to interpret the results as there can be many false positives.

Measuring total IgE is a waste of time – even smoking puts the levels up.

For aero-allergens and foods (other than in those with life-threatening anaphylaxis) there's no reason why skin-prick tests could not be done in primary care.

I strongly believe we should run allergy networks where each practice-based commissioning cluster has a GP or nurse who performs skin-prick tests, provides information and – in liaison with the local allergy centre – manages the allergy needs of the local population. This would enhance access to appropriate allergy advice and treatment and ensure that all receive a fair and consistent service at little increased cost to the NHS.

10. Are there any new developments in allergy GPs should be aware of?

The re-emergence of desensitisation as treatment for allergy to grass pollen and in the future other pollens, dust mite, cats and even peanuts means we need to enhance our allergy services. Furthermore desensitisation may be much more than simply treating symptoms. In children with pollen allergic rhino-conjunctivitis, desensitisation to their major allergen has led to a 50% reduction in the development of asthma and new allergic sensitisations – a huge benefit for them and for society.

If current studies with Grazax show similar benefit for sublingual therapy with other allergens then we will need to consider the early identification of such children and through treatment may halt the seemingly unstoppable rise in the prevalence of allergic rhinitis and asthma.

Dr Alaisdair Stewart is a consultant chest and allergy consultant at Medway NHS Foundation Trust

Competing interests Dr Stewart has been engaged as a speaker and has been sponsored to attend scientific conferences by ALK-Abello, Astra Zeneca, GSK, MSD and Schering Plough

What I will do now What I will do now

Dr Linden Ruckert considers the responses to her questions
Patients who develop allergy always ask ‘why and why now?', so it helps to have some expert information.
I'm interested in trying montelukast for unresponsive rhino-conjunctivitis but it is useful to be reminded of the product licence.
I'll explain to patients that oral allergy can wax and wane. Eczema and children will remain a problem but it's reassuring to be able to explain that most cases will resolve between the age of three and five. It is also worth being reminded that a cell-mediated response may take 24 hours to develop when trying to work out any association.
‘Allergy tests' are another common request and I don't do blood tests. It would be useful to have skin-prick testing in the community.
I'll take a more careful history in refractory rhinitis and consider the other causes. Salicylates and their occurrence in food is something I'd forgotten. Perhaps asking about rhinitis should be a routine part of an asthma check?
Perhaps when the cost of Grazax is less it can be more widely used, which would be great as so many young people are plagued by hay fever.

Dr Ruckert is a GP in north London

thps allergy If possible skin prick testing should be chosen over RAST Skin prick testing

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