Overview
Airborne allergenic pollens are an important group of allergens that cause allergic asthma, and hundreds of plant pollens are known to cause sensitization in humans. Pollen-induced allergic diseases include seasonal allergic rhinitis, allergic conjunctivitis, allergic dermatosis and allergic asthma. As inhaled pollen must pass through the upper respiratory tract before entering the lower respiratory tract, it is often accompanied by obvious upper respiratory symptoms, and most patients have upper respiratory symptoms first, followed by lower respiratory allergic symptoms such as coughing, phlegm and asthma.
Causes
There are many kinds of allergenic pollen in the atmosphere, different countries, different regions, different altitudes and different seasons can have different allergenic pollen, due to China’s north and south across the temperate zone and subtropical, the temperature varies greatly, coupled with the east-west spanning the large, geographic and altitude effects, allergenic pollen species have greater regional differences. Guangdong, Guangxi and Hainan area to subtropical plants, the Yangtze River basin area to temperate plants, northeast, northwest, and north China to cold-hardy plants.
Symptoms
Pollen allergic asthma is a kind of allergic disease manifested in the lower respiratory tract, mostly accompanied by obvious upper respiratory tract symptoms, most of the patients have upper respiratory tract symptoms first, followed by lower respiratory tract allergic symptoms such as cough, sputum and asthma. It starts with an irritating dry cough during pollen dispersal and worsens to a wheezing attack, with signs and symptoms of wheezing similar to those of other bronchial asthma. Before the asthma attack, patients usually have several floral nasal or pharyngeal symptoms, but there are also a small number of patients without any aura symptoms, the onset of asthma attacks as the first symptom. Its clinical features are mainly:
1. Seasonal attacks
The onset of asthma and other symptoms coincide with the flowering period of plants, are relatively fixed in the period of the attack, the duration of the seasonal attacks of the patient is less than a few days, more than a few months, to be pollen dispersal period, the condition of natural relief. Some patients with pollen allergy who are allergic to other allergens such as house dust and dust mites may have perennial attacks and seasonal exacerbations.
2. Obvious regional
Pollen allergic asthma has obvious regional characteristics, the so-called regional characteristics means that the patient usually only in the allergic pollen dispersal area onset, move to the pollen dispersal area can be quickly relieved.
3. Often accompanied by upper respiratory tract or other allergic symptoms
Before or at the same time with the attack of obvious upper respiratory tract allergy symptoms and other allergic symptoms. Patients often have a history of allergic rhinitis, allergic conjunctivitis or allergic skin disease for several years or even decades at the beginning of the attack, and then gradually involve the lower respiratory tract and cause asthma symptoms.
(1) Upper respiratory tract allergy symptoms and signs mainly include nasal or pharyngeal allergy. Nasal symptoms include seasonal allergic rhinitis symptoms such as itchy nose, sneezing and watery nasal discharge, which may be accompanied by itchy ears and palate. The itchy nose is predominantly in the tip and vestibule of the nose, and the patient presents with repeated nose rubbing. Sneezing can be several or even dozens of sneezes at a time, accompanied by a large amount of watery or white mucus-like nasal discharge at the same time as or after the sneezing episodes. Most patients have alternating nasal congestion or persistent nasal congestion, which can also lead to decreased or absent sense of smell. The above nasal symptoms are obviously related to seasonality, so it is called seasonal allergic rhinitis. Pharyngeal symptoms include pharyngeal itching, foreign body sensation or irritation in the pharynx, and in a few cases, irritating cough due to pharyngeal secretions.
(2) Other allergic symptoms include eye and skin allergies. Eye symptoms include itching, tearing, redness and swelling of the conjunctiva and eyelids, etc. Skin swelling is often manifested as itching of the face, limbs and other exposed parts of the skin, and eczema-like changes can be seen in severe cases.
4. Age of onset and atopic qualities
The age of onset of pollen allergic asthma is mainly young and middle-aged patients, children and elderly patients are usually less common. Pollen allergic asthma is characterized by atopic qualities, often with a family and personal history of allergic reactions.
Examination
1. Skin prick test
Skin prick test is a specific test that is widely used in clinical practice. Usually the pollen allergen dip is diluted and then subjected to skin prick test (Prick test) or intradermal test (Intradermal test).
2. Bronchial excitation test
This is a test method to simulate pollen allergic asthma attack, the result is more reliable, when the result of specific skin test is difficult to determine, this test method can achieve more reliable results.
3. Nasal mucosa excitation test
Since the nasal mucosa and bronchial mucosa belong to the same respiratory mucosa epithelium, the results of this test can usually reflect the sensitivity of the bronchial tubes to pollen more accurately.
4. Conjunctival excitation test
Dilute the pollen infusion and drop it on the conjunctiva of the eyes, observe whether there are positive manifestations such as itchy eyes, tearing and congestion. The advantage of the conjunctival test is that it is safe, and the allergen can be removed by rinsing in case of severe allergic reaction.
Diagnosis
The correct diagnosis of pollen allergic asthma is based on the correct determination of whether bronchial asthma is clinically present and whether the asthma attack is related to exposure to pollen allergens. The diagnosis of pollen allergic asthma is based on history, symptoms and signs of an attack, family history of tuberculosis, and necessary laboratory tests, including pulmonary function tests, airway hyperresponsiveness measurements, and immunologic tests for allergens. A positive pollen allergen-specific bronchial provocation test (BPT) is the most direct evidence of airway hypersensitivity to pollen allergens. Because skin prick test (SPT), S-IgE, and S-IgG can be used as etiologic basis, the use of these indicators is more specific in the presence of airway hyperreactivity in patients and can be used selectively according to conditions. However, the combined use of multiple immunologic indicators can confirm the etiology of asthma in different senses in order to increase the correctness of the diagnosis of pollen allergic asthma.
Treatment
The specific treatment of pollen allergic asthma refers to the etiological measures taken for the sensitized pollen, because of the strong targeting of the specific treatment, the clinical efficacy is more certain and the side effects are rare.
1. Avoid contact with pollen
Avoiding exposure to pollen can usually prevent asthma attacks. However, in practice, it is difficult to make patients completely avoid contact with pollen. When a patient with bronchial asthma is diagnosed with pollen allergy, he should first try to find out what kind of pollen he is allergic to, so that he can avoid or reduce the contact with the pollen according to the dispersion of that kind of pollen in the local atmosphere at the corresponding time.
2.Desensitization therapy
Also known as specific immunotherapy or desensitization therapy, its purpose is to improve the body’s ability to tolerate the corresponding allergenic pollen. At present, there are three kinds of desensitization therapies commonly used in clinical practice.
(1) Pre-seasonal desensitization therapy Usually, the treatment is started 3 months before the arrival of pollen season, and the injections are given 2 to 3 times per week, gradually increasing the injection dose of allergens from low to high concentration, and reaching the concentration of 1:100 before the season, so as to enable the organism to produce sufficient IgG closed antibody when the pollen season arrives, and then the maintenance injections are given 1 to 2 times per week, and the treatment can be stopped in the last month of the season of onset of the disease.
(2) Conventional immunotherapy Conventional immunotherapy is a kind of desensitization therapy carried out all year round, by injecting pollen infusion of increasing concentration twice a week, and strive to reach the maximum tolerance to the corresponding allergenic pollen in 3-4 months, at this time, the body can produce enough specific IgG closed antibody, so as to alleviate or disappear the clinical symptoms of pollen allergic asthma, and then switch to maintenance injection therapy once or twice a week, or even once every 2 weeks, and then maintain injection once or twice a week. Then switch to maintenance injection therapy once or twice a week or even every 2 weeks, and shorten the interval of desensitization injection to twice a week before the next pollen season. Conventional immunotherapy usually requires continuous treatment for 3 to 5 years or more to consolidate the efficacy.
(3) Blitz immunotherapy Blitz immunotherapy usually adopts a day-by-day injection method or several injections per day, aiming to reach the maximum tolerance to the corresponding allergenic pollen within 1 week to 1 month, so as to prevent or reduce clinical symptoms. Blitz immunotherapy can significantly shorten the duration of specific immunotherapy, and together with pre-seasonal desensitization, it can even shorten the duration of treatment. However, some studies have shown that surprise immunotherapy may increase delayed-phase asthmatic reactions, so it should be used with caution when hospitalized under close observation by a specialist.
3. Preventive treatment
Prevention of pollen allergic asthma is more important, but because pollen prevention measures are more difficult to implement, treatment can be based on preventive measures or in conjunction with preventive measures.
(1) Mast cell membrane stabilizers Mast cell membrane stabilizers are the main drugs used in the prevention and treatment of pollen allergic asthma. Inhalation before the season can effectively prevent pollen allergic asthma attacks. Currently, the suspension aerosol is more commonly used in the clinic. Inhalation is usually started 3 weeks before the seasonal attack. ② Trinilast is an effective oral mast cell protector, usually started 2 weeks before the onset of an attack. (iii) Azelastine A new drug for the prevention and treatment of allergic asthma, it has both mast cell membrane and other inflammatory cell membrane stabilizing effects and antagonistic effects on a variety of inflammatory mediators.
(2) Antihistamine drugs The first generation of antihistamine drugs represented by chlorpheniramine has better efficacy in the prevention and treatment of pollen allergic asthma, but due to side effects such as drowsiness and other limitations on the use of its use, and now often use the second generation of new antihistamine drugs without drowsiness. Loratadine is a second-generation antihistamine with a long duration of action and no central nervous system inhibition. Loratadine has a faster onset of action and can effectively control pollen allergic symptoms. Tefenadine is also a second-generation antihistamine without central nervous system inhibition. ③ Cetirizine is also a second-generation antihistamine, the effect of 1 hour after oral peak, the effect of time can last 24 hours, the drug in addition to antagonizing the role of histamine, but also inhibit the eosinophilic infiltration of the inflammatory zone. ④ ketotifen Its pharmacological mechanism is more complex, in addition to the antihistamine effect, but also has the role of inflammatory cell membrane stabilization. The drug has mild drowsiness, and the drowsiness can be reduced or disappeared after 2-3 weeks of continuous use.
(3) Glucocorticoids, including inhalation and systemic administration of two routes, is currently based on inhalation. Inhaled glucocorticosteroid preparations include fluticasone and budesonide, etc. Usually, inhalation should be started 1 week before the pollen season, and stopped 1 week before the end of the season. The efficacy of glucocorticoid inhalation therapy is more reliable, and the side effects are greatly reduced compared with systemic medication. Inhaled glucocorticoid can be considered for patients who are ineffective on oral antihistamines and inhaled cromoglycate.
(4) Symptomatic treatment As the degree of attack of pollen allergic asthma is usually mild, if asthma symptoms are given to inhalation of salbutamol aerosol and other β2-agonists can control the symptoms, and when the condition is more serious, it can also be used with the systemic use of glucocorticosteroids at the same time as the inhalation or oral β2-agonists, but also with the oral theophylline class of drugs. Patients with ocular allergy can use topical cromoglycolic acid ophthalmic solution.