|
|
|
 
 |
Allergy |
 |
|
| An allergy is an abnormal, acquired sensitivity to a given substance, including pollen, drugs, or numerous environmental triggers. The term was coined by the Viennese pediatrician Clemens von Pirquet in 1906 after noting that some of his patients were hypersensitive to normally innocuous entities such as dust, pollen, or certain foods. |
History |
| Historically, all forms of hypersensitivity were classified as allergies, and all thought to be caused by an improper activation of the antibody class called Immunoglobulin E - Teruka and Kimishige Ishizaka were among the first to isolate and describe IgE in the 1960s. Later, it became clear that several different disease mechanisms were implicated, with the common link between these varying hypersensitivities being a disordered activation of the immune system in one way or another. A new classification scheme was designed by P. Gell and R. Coombs[5] to reflect what were then rebaptized hypersensitivity reactions. The word "allergy" was then restricted to type I hypersensitivities, which are caused by the classical IgE mechanism. |
Signs and symptoms |
Allergy is a local or systemic inflammatory response to allergens. Local symptoms are:
- Nose: swelling of the nasal mucosa (allergic rhinitis)
- Eyes: redness and itching of the conjunctiva (allergic conjunctivitis)
- Airways: Sneezing, bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as anaphylaxis.
- Ears: feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.
- Skin: various rashes, such as eczema, hives (urticaria) and contact dermatitis.
- A headache from sinus pressure can arise if inflammation swells tissue surrounding the tiny sinus drains.
Allergic rhinitis afflicts 20% of the US population. Also known as hayfever, symptoms can be in response to airborne pollen. Asthmatics are often allergic to dust mites. Apart from ambient allergens, allergic reactions can result from foods, insect stings and reactions to medications.
Systemic allergic response is also called anaphylaxis; multiple systems can be affected including the digestive system, the respiratory system, and the circulatory system. Depending of the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma and even death. This type of reaction can be triggered suddenly or the onset can be delayed. The severity of this type of allergic response often requires injections of epinephrine, sometimes through a device known as the Epi-Pen auto-injector. The nature of anaphylaxis is such that the reaction can seemingly be subsiding, but may recur throughout a prolonged period of time. |
Diagnosis |
Before a diagnosis of allergic disease can be confirmed, possible differential causation should be carefully considered and included or excluded. Vasomotor rhinitis is one of many maladies that can mimic many of the symptoms of allergic rhinitis, underscoring the need for professional differential diagnosis.
Once a diagnosis of asthma, rhinitis, anaphylaxis, or some other allergic disease has been made, there are several methods for finding out what the patient is allergic to. |
Skin testing |
For assessing the presence of specific IgE antibodies, allergy skin testing, when possible, is the preferred method in comparison with various blood allergy tests because it is more sensitive and specific, simpler to use, and less expensive. Different blood allergy testing methods are currently available; the radioallergosorbent test (RAST) test method, which uses radioactive isotopes for testing, has largely been replaced by more modern methods.
The typical method of diagnosis and monitoring of Type I Hypersensitivity is skin testing, also known as "puncture testing" and "prick testing" due to the series of tiny puncture or pricks made into the patient's skin. Small amounts of suspected allergens and/or their extracts (pollen, grass, mite proteins, peanut extract, etc.) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected "intradermally" into the patient's skin, with a needle and syringe. Common areas for testing include the inside forearm and the back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to a full-blown hive (called "wheal and flare") in more sensitive patients.
After performing the skin test and receiving results, the nurse may apply a skin cream, perhaps a corticosteriod cream, to the test area to reduce discomfort (such as itching and inflammation).
Considerations with skin test
The skin prick test is the most preferred means of testing because of its simplicity, economic implications and its accuracy relative to the other tests available.
Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/- meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction.
Theoretical concerns include how to choose patients, interpret results, and maintain safety. If a serious life threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease or has not avoided antihistamines for several days. Additionally, some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.
Some people may display a small, delayed reaction that can occur up to 6 hours after application of the allergen and last up to 72 hours. It is often easily treated with anti-inflammatory creams. Interpretation by well-trained allergists is often guided by relevant literature which can offer calculation of 95% and 99% predicted probabilities using logistic regression revealed predictive decision points.
Another consideration with the application of previously un-encountered insect venom allergen is the theoretical possibility that this minute exposure can actually sensitize one to these allergen, causing the inception of a new sensitivity, but such a development is almost unheard of in clinical experience. For all these reasons skin testing should be offered by individuals with advanced training in the diagnosis and treatment of allergic disease.
Blood testing
This kind of testing is also known as a "total IgE level". This method measures the total amount of IgE contained within the patient's serum. This can be determined through the use of radiometric and colormetric immunoassays. The levels of IgE specific to certain allergens can be measured through use of various blood allergy test methods. The radioallergosorbent test (RAST) method uses radioactive isotopes for the measuring process. Other newer methods use colorimetric or fluorometric technology. Some "screening" test methods are intended to provide qualitative test results, giving a "yes" or "no" answer in patients with suspected allergic sensitization. One such method has a sensitivity of about 70.8% and a positive predictive value of 72.6% according to a large study.
A low total IgE level is not useful to rule out sensitization to common inhalant allergens. Statistical methods, such as ROC curves, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with specific allergy tests for a carefully chosen allergens is often warranted. |
Treatment |
| There have been enormous improvements in mainstream medical treatments developed by allergists. Recently, advances in anaphylaxis and hypersensitivity reactions to foods, drugs, and insects and in allergic skin disease include: the identification of food proteins to which IgE binding is associated with severe reactions, improvements in skin prick test predictions; evaluation of the atopy patch test; and advances in yellow jacket sting outcomes predictions and a rapidly disintegrating epinephrine tablet and development of low-allergen foods, and anti-IL-5 for eosinophilic diseases |
|
|
|
| |
| |
|
|
|
|
|
Quick search for drug information
|
|
|
|
|
|
|
