Food allergy in children

Introduction to children's food allergy Food allergy (foodallergy), also known as allergicreaction of digestive system or allergic gastroenteritis, food allergy, etc., is caused by certain food or food additives, and IgE-mediated and non-IgE Mediates an immune response that leads to an allergic reaction in the digestive system or systemic. basic knowledge Proportion of disease: 10% probability of illness in infants and young children Susceptible people: children Mode of infection: non-infectious Complications: bronchial asthma, allergic purpura, arrhythmia

Pediatric food allergic etiology

(1) Causes of the disease

1. Food-induced allergies

There are five ways to induce pediatric allergies: gastrointestinal ingestion, respiratory inhalation, skin contact or injection, through human milk and placenta.

2. Food allergen

Food allergens refer to food antigen molecules that cause immune responses. Almost all food allergens are proteins, most of which are water-soluble glycoproteins with a molecular weight of 100,000 to 600,000. Each food protein may contain several different types. The allergens, food allergens have the following characteristics:

(1) Any food can induce allergies: but the common food allergens in children are milk, eggs, and soybeans. Milk and eggs are the most common allergens in young children. Sensitized foods are also different in eating habits in different regions. Different, peanut is a common allergen for children and adults. Seafood is not a major allergen in children. Nut-induced allergies are rare in children. Although any food can be sensitized, about 90% of allergic reactions are caused by a small number of foods. Caused by, such as milk, eggs, peanuts and wheat.

(2) Only some components of food are allergenic: in milk and eggs, for example, at least 5 kinds of milk are allergenic, among which casein, beta-lactoglobulin, -LC The most allergenic, the egg yolk in the egg has quite a few allergens, and the egg albumin and egg mucin in egg white are the most common allergens in eggs.

(3) Variability of food allergenicity: Heating can reduce the allergenicity of most foods, and the acidity of the stomach and the presence of digestive enzymes can reduce the allergenicity of food.

(4) Cross-reactivity between foods: different proteins may have a common antigenic determinant, making the allergen cross-reactive, such as at least 50% of milk allergies are also allergic to goat milk, those who are allergic to eggs may be other Bird eggs are also allergic, cross-reaction does not exist between milk and beef, and does not exist between eggs and chicken. Plant cross-reactivity is more obvious than animals, such as those who are allergic to soybeans may also be other to legumes. Members such as lentils, cockroaches and other allergies, patients with allergies to pollen will also respond to fruits and vegetables, such as those who are allergic to birch pollen, also respond to apples, hazelnuts, peaches, apricots, cherries, carrots, etc. It also responds to umbelliferous vegetables such as celery, fennel and carrots.

(5) Allergic to intermediate metabolites of food: very rare, patients often have symptoms 2 to 3 hours after eating.

3. Genetic factors

Food allergies are related to genetics. One of the parents has a history of food allergies. The prevalence of their children is 30%. If both parents suffer from this disease, the prevalence of their children is as high as 60%.

4. Anatomical factors

The non-specific and specific mucosal barrier system of the human gastrointestinal tract can limit the invasion of intact protein antigens, and the food antigen entering the intestinal tract combines with secretory IgA (SIgA) to form an antigen-antibody complex, which limits intestinal to food antigens. Absorption, thereby directly or indirectly reducing the immune response to food proteins, pediatric digestive tract mucosa soft, high vascular permeability, digestive tract barrier function, various food allergens easily enter the blood through the intestinal mucosa, causing allergic reactions, The level of IgA in infants under 3 months is lower, and the number of plasma cells producing SIgA in the lamina propria is less. When the digestion, absorption process and mucosal immune abnormalities occur, allergens of various foods are easily passed through the intestinal mucosa. Allergic gastroenteritis.

5. Other factors

Gastrointestinal inflammation is one of the causes of increased incidence of intestinal allergies. This is due to gastrointestinal mucosal damage caused by digestive tract inflammation, which increases the permeability of the gastrointestinal mucosa, causing excessive food antigens to be absorbed and metamorphosis. reaction.

(two) pathogenesis

The sensitizing antigen activates the IgE plasma cells of the intestinal lamina propria, produces a large amount of IgE antibodies, and binds to mast cells, immobilized on the surface of these cells, when the allergen in the food re-enters the body, with the surface of the gastrointestinal mucosa mast cells IgE combines to activate mast cells, degranulate, release a series of inflammatory mediators involved in allergic reactions, increase vascular permeability, cause type I allergic reactions, and some antigenic substances can also selectively interact with plasma cells IgG, IgM, IgA or T cells bind to form an immune complex, causing local or (and) systemic type III or IV allergies, while age, food digestion, gastrointestinal permeability, food antigen structure, Genetic factors can affect the occurrence of food allergic reactions. Food allergies are most common in the first few years after birth. Most children are resistant to the food when they are 2 to 3 years old, and the symptoms disappear. IgE mediators may It lasts for a long time, and the severity of the beginning is not related to the disappearance of clinical symptoms in the future. However, due to the incompleteness of food allergens, especially in children, it is sensitive. Of persistence.

Pediatric food allergy prevention

Children with high risk of atopic disease (referring to one or both parents with atopic disease), especially during the first 3 to 6 months after birth, encourage breastfeeding, and remember that many food allergic infants later Other atopic diseases have occurred, so in the case of infants with a family history of allergies, the physician should tell the parents about this possibility, advise them not to smoke, do not raise animals indoors, and keep the indoor environment clean and hygienic.

Pediatric food allergy complications Complications, bronchial asthma, allergic purpura, arrhythmia

The most common manifestations of extraintestinal symptoms are angioedema and various rashes and eczema. In addition, it can cause rhinitis, conjunctivitis, recurrent oral ulcers, bronchial asthma, allergic purpura, arrhythmia, headache, dizziness, etc., and even systemic reactions to shock. There are reports of sudden death syndrome in infant food allergies, which should be highly valued.

Pediatric food allergic symptoms common symptoms allergic dermatitis herpes diarrhea irritability abdominal pain nausea malabsorption syndrome exhaust multiple skin itching intestinal bleeding

The severity of clinical manifestations is related to the strength of allergens in food and the susceptibility of the host.

1. IgE-mediated food allergic clinical symptoms appear faster, can be a few minutes after eating to 1 ~ 2h, sometimes very small can cause very serious allergic symptoms, in terms of the order of symptoms, the earliest appearance It is skin, mucous membrane symptoms, respiratory symptoms such as asthma appear late or not, but severe cases are often accompanied by respiratory symptoms, food-induced asthma is more common in infants, except for inhalation, generally combined with other allergic symptoms, the year Although long-term and adult foods can induce a variety of allergic symptoms including shock, but asthma is rare, food generally does not cause allergic rhinitis, allergic rhinitis as the only symptom of food allergies is very rare.

Allergic eosinophilic gastro-intestinal disease: characterized by EOS infiltration in the stomach or small intestine wall, often with increased peripheral blood EOS, EOS infiltration involving the mucosa of the stomach or small intestine, muscle layer and/or serosa, often Post-meal nausea and vomiting, abdominal pain, intermittent diarrhea, infant growth and development stagnation, muscle infiltration leading to thickening and stiffness of the stomach and small intestine, clinical signs of obstruction, subserosal infiltration generally expressed as EOS ascites, this The pathogenesis of the disease is unknown. Some of the patients have aggravated symptoms after eating certain foods. They involve type I allergic reactions. The patient's duodenal juice and serum have elevated IgE, and more with atopic diseases. Inhaled skin prick test is positive, can be secondary to iron deficiency anemia and hypoalbuminemia, the disease often involving infants 6 to 18 months, diagnosis based on gastrointestinal biopsy, characteristic EOS increased, mucosal patients often There are atopic symptoms, elevated serum total IgE, multiple allergen skin test and RAST, positive reaction, increased peripheral blood EOS, anemia, etc. Excluding allergic foods for up to 12 weeks, symptoms will disappear, intestinal tissue will Back to normal.

Infant colic: manifested as infantile paroxysmal irritability, extreme pain, shouting, leg contracture, abdominal distension, and more exhaustion. It usually occurs 2 to 4 weeks after birth, and healed in 3 to 4 months. Diagnosis relies on elimination of attacks. Exclude the test.

Oral (allergic) allergic syndrome (OAS): After a few minutes of eating one or more fruits or vegetables, the oropharynx, such as the lips, tongue, upper jaw and throat, itching and swelling, a small number of patients Systemic allergic symptoms occur in patients with hay fever or suggest that hay fever may occur after the occurrence of cross-reactivity between pollen and fruit or vegetables.

2. Non-IgE (ie IgM, IgG or combination of several antibodies) mediated food allergy II, III, IV immunopathology can be involved, but direct evidence is rare, it is believed that some food adverse reactions involve non-IgE Immune mechanism, involving type II such as milk-induced thrombocytopenia; involving type III and type IV, such as herpes-like dermatitis, gluten-sensitized bowel disease, milk-induced intestinal bleeding, food-induced enterocolitis syndrome, food-induced absorption Bad syndrome, etc., can also cause allergic pneumonia, bronchial asthma, atopic dermatitis, contact dermatitis, allergic purpura and so on.

Pediatric food allergy check

1. Non-specific laboratory examination In most cases, blood biochemistry and three routine examinations were found to be abnormal. A small number of peripheral blood had mild increase in eosinophils, hypochromic anemia, fecal occult blood test and Charat-Leyden crystal positive, serum total IgE. Increased, digestive endoscopy can be normal or non-specific gastrointestinal mucosal hemorrhage, edema, these can not be used as a basis for the diagnosis of food allergy.

2. Specificity check

(1) Skin test of food antigen: According to the antigen and the corresponding IgE binding on the surface of mast cells, stimulate the degranulation of mast cells and cause the corresponding clinical manifestations, which is the preliminary screening of allergic foods. The main method is to provide skin test results for a variety of foods at 15 to 20 minutes. The following points should be noted before implementing the test:

1 The amount of food that is stimulated should be strictly controlled.

2 Fasting suspicious food 2 weeks before the challenge.

3 Anti-allergic drugs were stopped 1 week before the challenge, and other treatments remained at the lowest level.

4 Judging by standard scoring method.

5 The skin prick test may occasionally induce a systemic allergic reaction and should be carried out under conditions of rescue equipment.

Children over 3 years old have a negative skin test, which generally excludes allergies to the food. Positive positives generally indicate that the food is allergic, but there are certain false positives. It is more difficult for children under 3 years old to have a skin test, and the possibility of false negative is greater.

(2) Elimination of diet: The patient first eats a normal or basic diet within 1 to 2 weeks. The purpose is to remove the original food in the digestive tract, so that all symptoms of food allergy disappear, and the period is clear, then Enter the food-promoting period, add a food every 2 to 3 days until the symptoms are triggered, and repeat the test for the food that is positive for the test to clear the allergenic food. The food exclusion method is positive, only the food allergy is indicated, and Can not be fully confirmed, because other food abnormal reactions can not be ruled out, it should be comprehensive judgment of other tests, the test is time-consuming, troublesome, but no special equipment and test conditions, suitable for outpatients.

(3) Radio allergen absorption test (RAST): It is the use of known food antigens to detect the presence or absence of corresponding IgE antibodies in the serum of patients. The method has high accuracy, low false positive rate, and is not used by patients. The impact, but expensive, and the inability to detect multiple antigens simultaneously.

(4) The double-blind placebo controlled food challenge (DBPCFC): also known as the food provocative test, is a standard indicator for the diagnosis of allergies caused by a particular food. During the first week of the food challenge test and during the challenge period, patients should strictly avoid contact with and consume the tested food and suspected allergic foods, and stimulate the oral administration of small doses of suspected allergic food (or placebo). 60min dose doubled, observe the following indicators: 1 nausea, vomiting, diarrhea, abdominal pain and other gastrointestinal and gastrointestinal symptoms.

2 The neutrophils of peripheral blood increased more than 3.5×109/L before and 6 to 8 hours after the test.

3 bloody stool or fecal occult blood test was positive.

4 There are white blood cells in the mucus of the stool.

After 5 Hansel staining, Charact-Leyden crystals formed by eosinophil fragments were found in the feces.

The above indicators have 3 positive diagnoses, and 2 consecutive positives are suspected. Further observation is needed. If the symptoms are not triggered, the total amount of food has increased to 8g (dry weight) or the usual food intake, which can rule out allergic reactions. The delayed response can be further tested with normal food intake.

1. Radiological diagnostic X-ray examination has special important value, including chest fluoroscopy, radiography, gastrointestinal angiography, etc., which has important diagnostic significance for some allergic diseases. In addition, X-ray examination can help identify other non-allergic reactions. Sexual diseases and elimination of complications, modern imaging diagnosis including: B-ultrasound, CT, magnetic resonance, etc., if necessary, also applied to the auxiliary diagnosis of allergic diseases.

2. Pharmacy diagnosis For some allergic diseases, some drugs that are effective for allergic reactions, such as adrenaline, 2 receptor agonists, various anti-tissues, can also be used in cases where various tests cannot be confirmed. Amine drugs, various adrenocortical hormone drugs, etc., for exploratory treatment, such as the efficacy of medication, can be cited from the side of the diagnosis of allergic disease, but in the diagnosis of this exploratory drug, must fully consider the condition, Exclude contraindications and possible side effects of the test drug on the patient.

Diagnosis and diagnosis of pediatric food allergy

diagnosis

The diagnosis of food allergies is based on detailed medical history, skin test or RAST results. If IgE is suspected, the food should be excluded and a blind attack should be performed if necessary, but there is a severe allergic reaction in the medical history or a clear diagnosis. Do not do, suspected of non-IgE-mediated food-induced gastrointestinal diseases, the diagnosis of biopsy before and after the attack, unconditional food exclusion and attack test, according to medical history and / or skin test Suspected IgE-mediated disease or food-induced enterocolitis, suspected food should be excluded for 1 to 2 weeks, other gastrointestinal allergic diseases can rule out suspicious food for up to 12 weeks, if the symptoms are not improved, it is unlikely to be food Allergic reactions, can not be based on skin tests or RAST to make a diagnosis of type I food allergies, many patients are misdiagnosed as food-induced food allergies, and avoid food they should not fast, so the history Blind attacks with food are important for the diagnosis of the cause.

Differential diagnosis

Symptoms caused by food allergies are diverse and non-specific, and should be differentiated from digestive tract and systemic diseases caused by non-allergic reactions, such as dyspepsia caused by various causes, cholelithiasis, inflammatory bowel disease, celiac disease, etc.

The adverse reactions caused by eating certain foods cannot be considered as food allergies. The concept of abnormal food reactions proposed by the American Society of Allergy and Immunology in 1984 is quoted below.

1. Abnormal reaction of food A food abnormality is a general concept that applies to all abnormal reactions caused by ingested foods and/or food additives, including the body's immune response to food ingredients or additives. (IgE-mediated and non-IgE-mediated immune responses) and non-immune side effects such as food intolerance, toxicity, metabolic, pharmacological and idiosyncratic responses, and abnormal reactions caused by psychosocial factors .

2. food intolerance (food intolerance) refers to abnormal physiological reactions caused by food and / or additives, is a non-immune reaction caused by food or additives (such as toxic, pharmacological, metabolic, infection) Sexual reaction and other abnormal reactions caused by non-immune factors), the main difference between it and food abnormal reaction is that it does not involve immune response, but it can be involved in the release of inflammatory mediators by mast cells caused by non-immune factors.

3. food poisoning (poisoning) food poisoning is a systemic disease caused by eating foods and/or food additives that are contaminated with poisons or are inherently toxic, accumulating a certain amount in the effect site, and can be classified into bacterial diseases. And non-bacterial food poisoning two categories, poisons can come from contaminated microorganisms and food itself (such as pufferfish, raw fish gallbladder, etc.), but also from other chemicals (such as arsenic, mercury, organophosphorus pesticides, etc.), this anomaly The response is generally without the involvement of immune factors.

4. Pharmacological food reaction Pharmacological food reaction refers to foods and their derivatives and/or food additives containing endogenous pharmacological substances (such as caffeine, histamine, etc.), intake into the body After a certain amount, the pharmacological effects and manifestations of a certain drug produced.

5. Food pseudo-allergy Pseudo-food allergies refer to food abnormalities caused by mental and psychological factors, and their clinical manifestations are similar to food allergies, but do not involve the release of chemical mediators mediated by immune mechanisms.

6. Food allergy/hypersensitivity Food allergy refers to the immune response caused by food or food additives in some people. It can be induced by eating a small amount of food. It has nothing to do with the physiological effects of food and/or food additives. The release of the chemical medium caused.

Food poisoning, pharmacological side effects and food intolerance generally do not involve the body's immune response, and food allergies are different, clinical should pay attention to distinguish, especially to avoid misdiagnosis of food allergies as food side effects or food intolerance Accepted.

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