Immunotherapy for allergic diseases (2)

 

 

So how do we treat allergies?  The most obvious answer is to avoid coming in contact with allergens.  To successfully practice allergen avoidance, we must first find out what the person is allergic to, and to confirm that these allergens are responsible for their symptoms.  A positive skin test will identify allergens that the patient responds to immunologically, but it still does not confirm that these allergens cause symptoms from day to day.   

 

A careful history will be very helpful, but sometimes, challenge studies might be needed.  Measuring the level of allergens in the patient’s living and working environment might also be useful.  For certain indoor allergens such as house dust mites and animal dander, avoidance measures can be extremely helpful.  The second line of treatment for allergies is drug treatment.   

 

Drugs such as antihistamines are used to counteract some of the symptoms of an allergic reaction.  They can be useful for mild cases but are frequently not successful in controlling more severe cases.  Steroid spray is also very useful in reducing the inflammation caused by an allergic reaction.  These treatments do not address the root of the problem, and symptoms promptly recur once the patient stops the treatments.

 

The only method to eliminate allergies is by immunotherapy.  This form of therapy aims to induce immunological tolerance to specific allergens, so that patients will no longer react to them when exposed.  Traditionally, immunotherapy (also called allergy injections or desensitization) is administered by repeated subcutaneous injections of purified allergen extracts.  

 

 This carries a risk of severe allergic reactions, and the injections must be administer under the supervision of an experienced allergist with adequate emergency support.  In experienced hands, immunotherapy is very safe, especially if standardized extracts are used.  In patients with insect sting allergy, immunotherapy is >99% effective in protecting the patients from future stings, and the effect appears to be lifelong after 3 to 5 years of continuous treatment.  The effectiveness of pollen immunotherapy has also been shown to last for at least 3 years after stopping treatment.

 

Newer forms of immunotherapy are being developed.  Sublingual immunotherapy uses a very high dose of allergen extract to be placed under the tongue for absorption.  Initial studies suggest that it might be effective for allergic rhinitis and possibly asthma.  More studies are needed to confirm its efficacy and also to determine its mechanism of action.  We are currently conducting a large clinical study, which will eventually involve 120 patients with allergic rhinitis, to evaluate sublingual immunotherapy against house dust mites.  

 

 Patients with moderate to severe allergic rhinitis will be recruited.  Skin tests to common allergens will be performed to confirm sensitization to house dust mites.  A nasal challenge study will be performed to confirm that house dust mites can indeed cause nasal symptoms.  The patients will first be given conventional drug therapy including an antihistamine and a nasal spray.   

 

Patients who do not derive satisfactory results from this treatment will be randomized to receive immunotherapy or placebo for one year.  The patients will be reevaluated every three months, and those that respond to treatment will have their nasal spray gradually withdrawn.  Patients will fill in a report of their symptoms every week.  At the end of one year, all patients on active treatment will continue for another year, and those on placebo will be switched to active treatment.  Immunological parameters in the blood and nasal washings will be evaluated at the beginning of the study and after one year.]

 

 

Reference information:  www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

Immunotherapy for allergic diseases (1)

 

 

 

Allergic diseases are some of the most common diseases in Hong Kong.  It has been estimated that up to 50% of school children suffer from symptoms of rhinitis, while about 15% of them have asthma and about 10% have eczema.  The incidence of allergic diseases is also increasing around the world, as a result of changes in our lifestyle and our environment.

 

Allergic rhinitis/conjunctivitis is a common problem that many sufferers simply ignore.  The symptoms include sneezing, itchy nose, itchy eyes, runny nose, watery eyes, congestion and post-nasal drip.  However, severe cases can be quite debilitating.  Children with allergic rhinitis have been shown to suffer from poor sleep, impaired learning, bad temper and hyperactivity.  Adults with allergic rhinitis are at risk of disorders of mood and sleep.  Severe allergic rhinitis might become complicated by sinus and middle ear infections, worsening of asthma, and might affect facial and dental development in children.

 

The cause of allergic rhinitis in any individual is dependent on his/her living and working environment.  In temperate climate, pollens are the most common causes.  However, in subtropical climates such as Hong Kong, indoor allergens such as house dust mites, mould spores, cockroaches and animal dander are the most common causes.  Exposure to allergens in the work environment is also very important.

 

Why do people develop allergies?  When we are first exposed to a foreign substance, through our skin, our respiratory tract or GI tract, our immune system will strive to recognize this substance.  In most cases, our immune system recognizes that these substances are harmless and ignores them.  This is a process called immunological tolerance.  Not only does the immune system ignore these antigens, it actually develops a response that actively suppresses any reaction to the antigens.  This active suppression can be passed on from one experimental animal to another by transferring immune cells called T cells.  In allergic individuals, this mechanism somehow failed to work for certain antigens (allergens), and they develop an immune response every time they encounter these antigens.  This immune response leads to allergic symptoms.

 

 

Reference information: www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult
physician before considering treatment and should not rely on the information above.

防治哮喘刻不容緩

當季節轉換時，環境溫度和濕度的轉變會令哮喘患者的呼吸道有不適的感覺，有些患者會在這個季節病情出現反覆，因此，每當春季來臨亦是哮喘發作的高峰期。

哮喘屬於支氣管收窄的疾病。患者因吸入了環境致敏原，如塵蟎、霉菌、動物毛髮、花粉或污濁空氣等而導致過敏性發炎，患者的氣管因發炎而引致氣管收窄，若發炎的情況嚴重更會令氣管的肌肉收縮而導致呼吸困難。有部份哮喘患者同時亦是鼻敏感或濕疹病人。

除此之外，亦有病人因阿士匹靈過敏症而誘發哮喘，此類病人多屬遺傳關係，而發病亦多在成年時候。

哮喘影響生活質素

一般而言，哮喘患者會有以下病徵：咳嗽、痰涎、呼吸困難、氣促、胸口有壓迫感及呼吸有喘鳴等，他們在發病時支氣管因發炎加劇而變得腫脹、狹窄，積有痰液及分泌物，令空氣不能順暢地出入肺部；所以會有喘鳴及呼吸困難的病徵，嚴重者更可以因此而窒息致命。

還有，很多哮喘患者有睡眠不足的問題，除了影響他們睡眠的質素外，間接亦影響他們的日常生活或工作表現；因此，若發現自己經常有上述的病徵時，便必須及早求診，以免病情進一步惡化。

 

 

 

參考資料: www.allergy.hk

以上所提供的資訊僅作為教育及參考用途，如果你有任何醫療問題，

應向自己的過敏病科醫生查詢，而不應單倚賴以上提供的資料。

常見致敏原:動物

 

 

常見的致敏原，亦是最容易引起敏感的動物，包括貓、狗、鼠類（小鼠、大鼠、倉鼠）、馬及鳥類等，以貓致敏原引起的敏感問題最多。貓致敏原在皮脂中產生，分泌後致敏原便會留在表皮和毛髮上，當患者接觸貓的毛屑後便會出現過敏反應。

不少人以為倘若家裏沒養貓狗，便不會接觸動物致敏原，但事實並非如此。以貓的致敏原為例，因它的黏性很強，大部份貓主的衣服都會帶有貓的致敏原，並跟隨左右，散佈在學校、圖書館及其他公眾場所等。

跟塵蟎相比，動物致敏原的平均體積較小，如貓的致敏原直徑約1mm，而塵蟎則有5－10mm。這麼細小且輕的致敏原，可以在空氣中懸浮一段較長的時間，因此當患者進入貓狗的範圍內，敏感反應很快便會出現，根本不需要與動物有直接接觸。 還有，有研究發現即使在沒有養貓狗的家居中，也有機會從鄰近地區傳入並測試到家中存有貓狗的致敏原。

瑞典曾有一項研究指出，課室內的空氣存在多少貓的致敏原，是跟這班學生的家中養貓有關；換句話說，若學生對貓敏感，剛巧班中有數位同學家中養貓，該名對貓敏感的學生很大機會有較嚴重的敏感症狀。就此研究後，不少瑞典的學校紛紛把養貓與沒有養貓的學生分隔上課。

參考資料: www.allergy.hk

以上所提供的資訊僅作為教育及參考用途，如果你有任何醫療問題，

應向自己的過敏病科醫生查詢，而不應單倚賴以上提供的資料。