Allergic gastroenteritis, also known as foodallergy or allergicreactionofdigestivesystem or foodallergy, is caused by IgE-mediated and non-IgE-mediated immune reactions to certain foods or food additives. It is caused by IgE-mediated and non-IgE-mediated immune reactions caused by a certain food or food additive, which leads to allergic reactions in the digestive system or systemic reactions.
Epidemiology]
The prevalence of food allergic reactions in children is about 6% to 8%, and cow’s milk is the most common allergic food accounting for 3% to 7.5% of them, with infants and children within 1 year of age being the most common. The incidence of food allergies decreases significantly with age. Patients with food allergies are often accompanied by bronchial asthma, with an incidence of about 6.8% to 17%, while the incidence of asthma in children with milk allergy can be as high as 26%.
[Etiology].
There are five ways to induce food allergy in children: gastrointestinal ingestion, respiratory inhalation, skin contact or injection, and entry through human milk and placenta.
Food allergens are food antigen molecules that can cause an immune response. Almost all food allergens are proteins, mostly water-soluble glycoproteins, with molecular weights of 100,000 to 600,000 Each food protein may contain several different allergens. Food allergens have the following characteristics.
Any food can induce allergic reactions: but common food allergens in pediatric patients are milk, eggs, soybeans, of which milk and eggs are the most common strong allergen sensitizing foods for young children also vary depending on regional dietary habits. Although any food can cause allergy, about 90% of allergic reactions are caused by a few foods, such as milk, eggs, peanuts and wheat.
Only some components of food are allergenic: milk and eggs, for example, have at least five allergens, with casein and beta-lactoglobulin (beta-LC) being the most allergenic. Egg yolks have relatively few allergens and egg albumin and egg mucin in egg whites are the most common allergens in eggs.
Variability of food allergenicity: Heating reduces the allergenicity of most foods. Increased acidity of the stomach and the presence of digestive enzymes can reduce the allergenicity of foods.
Cross-reactivity between foods: Different proteins can have common antigenic determinants, making allergens cross-reactive. For example, at least 50% of people allergic to cow’s milk are also allergic to goat’s milk. People allergic to eggs may also be allergic to eggs of other birds. Cross-reactivity does not exist between milk and beef, nor between eggs and chicken. Cross-reactivity is more pronounced in plants than in animals e.g. a person allergic to soy may also be allergic to other members of the legume family such as lentils, alfalfa, etc. Patients allergic to pollen also react to fruits and vegetables e.g. those allergic to birch pollen also react to apples, hazelnuts peaches, apricots, cherries, carrots, etc. Those allergic to Artemisia annua also react to umbelliferous vegetables such as celery, fennel and carrots.
Allergy to intermediate metabolites of food: very rare, patients mostly develop symptoms 2 to 3 h after eating
Genetic factors Food allergies are genetically linked. If one parent has a history of food allergy, the prevalence of their children is 30% and if both parents have the disease, the prevalence of their children is 60%.
The non-specific and specific mucosal barrier system of the human gastrointestinal tract can limit the invasion of intact protein antigens, while food antigens entering the intestine bind with secretory IgA (SIgA) to form antigen-antibody complexes, limiting the absorption of food antigens in the intestine and thus directly or indirectly reducing the immune response to food proteins. In infants under 3 months of age, the level of IgA is low and the number of SIgA-producing plasma cells in the lamina propria of the mucosa is low. When the digestion and absorption process and mucosal immunity are abnormal, allergic gastroenteritis occurs due to the easy entry of allergens from various foods into the bloodstream through the intestinal mucosa.
Other factors inflammation of the digestive tract is one of the reasons for the increased incidence of intestinal allergies. This is due to the damage of the gastrointestinal mucosa caused by inflammation of the digestive tract, which increases the permeability of the gastrointestinal mucosa and causes excess food antigens to be absorbed and metamorphic reactions to occur.
[Pathogenesis].
Allergenic antigen activates IgE plasma cells in the intestinal lamina propria to produce large amounts of IgE antibodies, which bind to mast cells and are fixed on the surface of these cells. When the allergen in food enters the body again and combines with IgE on the surface of mast cells in the gastrointestinal mucosa, the mast cells activate degranulation to release a series of inflammatory mediators involved in allergic reactions, increasing vascular permeability and causing type I metaplasia Some antigenic substances can also selectively bind to plasma cell IgG, IgM, IgA or T cells to form immune complexes, thus causing local or (and) systemic type III or IV allergic reactions, while age, the digestive process of food, the permeability of the gastrointestinal tract, and the structural genetic factors of food antigens can affect the occurrence of food allergic reactions. IgE-mediated reactions may last longer. The severity of the beginning is not related to the disappearance of clinical symptoms later, but the sensitivity persists due to incomplete avoidance of food allergens, especially in teenage children.
Clinical manifestations
The severity of clinical manifestations is related to the strength of the allergen in the food and the susceptibility of the host.
The clinical symptoms of mediated food allergic reactions appear quickly, from a few minutes to 1-2 h after eating, and sometimes a very small amount can cause very serious allergic symptoms. In terms of the order of symptoms, the earliest appearances are often skin and mucosal symptoms. Respiratory symptoms such as asthma appear later or do not appear but are often accompanied by respiratory symptoms in severe cases. In older children and adults, food can induce a variety of allergic symptoms, including shock, but asthma is uncommon. Food does not usually cause allergic rhinitis, and allergic rhinitis as the only symptom of food allergy is very rare.
Allergic eosinophilic gastrointestinal disease: characterized by EOS infiltration in the wall of the stomach or small intestine, often with an increase in peripheral blood EOS, which involves the mucosa, muscular layer and/or plasma membrane of the stomach or small intestine. Patients often present with postprandial nausea and vomiting, abdominal pain, intermittent diarrhea, and growth arrest in young infants. Myenteric infiltration leads to thickening and stiffening of the stomach and small intestine, and clinical signs of obstruction may be present. The subplasma infiltrate usually presents as EOS ascites. The pathogenic mechanism of this disease is unknown. Some of these patients have worsened symptoms after eating certain foods, involving type I allergic reactions, and patients with elevated IgE in duodenal fluid and serum mostly with atopic disease can develop iron deficiency anemia and hypoalbuminemia secondary to positive skin prick tests for a variety of foods and inhalants. The disease often affects infants 6 to 18 months of age. Diagnosis is based on gastrointestinal biopsy, and patients with the characteristic mucosal form of increased EOS often have atopic symptoms, elevated total serum IgE multiple allergen skin tests and RAST, positive reactions peripheral blood EOS increased anemia, etc. It takes up to 12 weeks for symptoms to resolve and intestinal tissues to return to normal with the exclusion of allergic foods.
Infantile colic: manifests as paroxysmal irritability in infants, extreme painful cries, leg curling, abdominal distension, and much exhaustion, usually develops 2 to 4 weeks after birth and resolves by 3 to 4 months. Diagnosis relies on exclusion of attack exclusion test
Oralallergysyndrome (OAS): Itching and swelling of the oropharynx, such as the lips, tongue and palate, and larynx a few minutes after eating one or more fruits or vegetables, and systemic allergic symptoms in a few children. It mostly occurs in patients with hay fever or suggests the possibility of hay fever later. This is due to cross-reactivity between pollen and fruits or vegetables.
Non-IgE (i.e. IgMIgG or a combination of several antibodies) mediated food allergic reactions type II, III, and IV immunopathology can be involved, but direct evidence is scarce and it is believed that some food adverse reactions involve non-IgE immune mechanisms. Those involving type II, such as milk-induced thrombocytopenia, and those involving types III and IV, such as herpes-like dermatitis, gluten-sensitizing enteropathy, milk-induced intestinal bleeding, food-induced small bowel colitis syndrome, and food-induced malabsorption syndrome. It can also cause allergic pneumonia, bronchial asthma allergic dermatitis, contact dermatitis allergic purpura, etc.
[Complications].
The most common extraintestinal symptoms are angioneurotic edema and various rashes and eczema. In addition, it can also cause rhinitis, conjunctivitis, recurrent oral ulcers, bronchial asthma, allergic purpura, cardiac arrhythmia, headache and dizziness, etc. It can even cause systemic reactions of anaphylaxis, and sudden death syndrome has been reported in infancy, which should be taken seriously.
Diagnosis
The diagnosis of food allergic reaction is based on a detailed medical history, skin test or RAST results. If IgE-mediated is suspected, blind attacks should be done if necessary to exclude the food in question, but not for those who have had severe allergic reactions in their medical history or for those with a clear diagnosis. The diagnosis of suspected non-IgE-mediated food-induced gastrointestinal disease requires biopsy before and after the attack, and food exclusion and attack tests should be done when not available. Small bowel colitis suspected to be IgE-mediated disease or food-induced based on history and/or skin test should exclude the suspected food for 1 to 2 weeks. Other gastrointestinal allergic diseases can exclude suspicious foods for up to 12 weeks. If symptoms do not improve, it is unlikely that the diagnosis of a food allergy cannot be made solely on the basis of a skin test or RAST for a type I food allergy. Many patients are misdiagnosed as having a food allergy due to a particular food on this basis and avoid foods they should not have abstained from therefore a history and blind attack of food is important for the diagnosis of etiology. It is also clinically noted that IgE and non-IgE types can co-exist or transform into each other, as well as the possibility that patients may be allergic to new food allergens at any time
Differential diagnosis]
The symptoms caused by food allergy are diverse and non-specific, and should be differentiated from digestive and systemic diseases caused by non-allergic reactions, such as dyspepsia, cholelithiasis, inflammatory bowel disease, celiac disease, etc.
Adverse reactions caused by the consumption of certain foods cannot all be considered as food allergies. The concept of abnormal food reactions proposed by the American Academy of Allergy and Immunology in 1984 is cited below.
Abnormal food reaction (abnormalreactionoffood) is a general concept that applies to all abnormal reactions caused by ingested food and/or food additives, including immune reactions (IgE-mediated and non-IgE-mediated immune reactions) and non-immune side reactions such as food intolerance, toxicity, and toxicities caused by food components or additives. Metabolic, pharmacological and idiosyncratic reactions, as well as abnormal reactions caused by psychological factors.
Food intolerance refers to abnormal physiological reactions caused by food and/or additives that are non-immune reactions caused by food or additives (such as toxic, pharmacological, metabolic infectious reactions and other abnormal reactions caused by non-immune factors), and the main difference between it and abnormal food reactions is that they do not involve immune reactions, but can be caused by non-immune factors The main difference with abnormal food reactions is that they do not involve an immune response, but can be caused by non-immune factors, such as the release of inflammatory mediators from mast cells.
Food poisoning (foodtoxicity/poisoning) is a systemic disease resulting from the accumulation of toxic food and/or food additives at the effect site due to the consumption of food contaminated with toxic substances or toxic in itself, and can be divided into two categories: bacterial and non-bacterial food poisoning. Toxins can come from contaminated microorganisms and the food itself (e.g., puffer fish, raw fish bile, etc.) or from other chemical substances (e.g., arsenic and mercury, organophosphorus pesticides, etc.). This abnormal reaction usually does not involve immune factors.
Pharmacologic foodreaction refers to the pharmacological effects and manifestations of a drug that is produced by food and its derivatives and/or food additives containing endogenous pharmacological substances (such as caffeine, histamine, etc.) when ingested into the body in certain amounts.
Foodpseudo-allergy refers to abnormal food reactions caused by mental and psychological factors. The clinical manifestations are similar to food allergy, but do not involve the release of chemical mediators mediated by immune mechanisms.
Food allergy/hypersensitivity refers to an immune response caused by food or food additives in some people. It can be triggered by the consumption of small amounts of the food in question, independent of the physiological effects of the food and/or food additives, and involves the release of chemical mediators induced by immune mechanisms.
Food poisoning, pharmacological-like side effects and food intolerance generally do not involve the body’s immune response and are different from allergic reactions to food, so clinical attention should be paid to distinguish them, especially to avoid misdiagnosing food allergic reactions as toxic side effects of food or food intolerance.
[Treatment].
Avoidance of allergens Once an allergen is identified, it should be strictly avoided, which is the most effective means of prevention and treatment. But “avoid” should be targeted, such as the most allergic part of the egg is the egg white, can eat the egg yolk part of the general 6 to 12 months after the child’s sensitivity to most food antigens disappeared.
Drugs are generally not advocated for long-term prevention with ketotifen and corticosteroids. The effect of oral cromoglycate is not certain. IT with food is also not advocated. but OAS can be IT with sensitizing pollen and after 1 year most patients have reduced sensitivity to pollen and plant foods. However, symptoms should be treated symptomatically when food has induced symptoms.
Prognosis and prevention]
The prognosis is generally good, and most of them gradually remit with age. However, improper management and migratory development of the disease often lead to malnutrition and growth disorders.
Children at high risk for atopic disease (meaning one or both parents have atopic disease) are encouraged to be breastfed, especially during the first 3-6 months of life. It should also be remembered that many infants with food allergies go on to develop other atopic diseases. Therefore, in the case of infants with a family history of atopic reactions, the physician should inform the parents of this possibility and advise them not to smoke and not to keep animals indoors to keep the indoor environment clean and sanitary.