Exogenous Allergic Alveolitis in Children

　　First, etiology

　　This condition is an immunological disease, and the organic dusts that cause hypersensitive pulmonary inflammation are common, including the following categories:

　　Thermophilic actinomycetes come from moldy hay, sugarcane, indoor humidifiers, air conditioners, etc.

　　Fungi such as Aspergillus, Alternaria, etc., come from barley, wood pulp, etc.

　　Animals such as birds, rodents, etc., come from pigeons, budgerigars, doves, mice, etc.

　　Second, pathogenesis

　　Many factors determine the nature of organic dust inhalation, with the host's reactivity being the first. Atopic individuals exhibit typical type I hypersensitivity reactions to organic dust, while non-atopic individuals may trigger type III hypersensitivity reactions caused by organic dust, with the specific change being the precipitation of antibodies. The second factor affecting the reaction is the nature and source of the antigen, with the size of the dust particles possibly being the most important, as the largest particles that can enter the alveoli are 4-6μm. If most of the particles are over 10μm, they will hang in the upper respiratory tract, and there will not be enough small particles to reach and damage the alveoli. The third factor is the exposure to organic dust, with the clinical manifestations of those with severe but intermittent exposure being different from those with less severe long-term exposure. It is generally considered to be a type III hypersensitivity reaction (due to the deposition of immune complexes), but lung biopsy did not find the characteristic pulmonary vasculitis of type III hypersensitivity reactions. Therefore, some people support the view of type IV hypersensitivity reaction (delayed reaction) because its histological damage in the acute phase is mainly lymphocytic infiltration in the alveolar wall, followed by mononuclear cell infiltration and scattered non-caseating giant cell granulomas, and later is the fibrosis and organization of lung tissue, obstructive bronchiolitis, which is consistent with type IV hypersensitivity reaction. However, there are also reports indicating that type II hypersensitivity reactions and non-immunological mechanisms are also involved in the pathogenesis of this disease. This disease is more common in children, with symptoms beginning 3-6 hours after inhalation of the antigen, reaching a peak at 6-8 hours, and disappearing around 24 hours. For example, the 'farmer's lung' caused by contacting straw containing fungi, and 'pigeon keeper's lung' caused by allergic reactions to animal proteins in bird droppings, etc. Some reports suggest that there is a certain association between the patient's tissue compatibility antigen (HLA) system and allergic pneumonia. For example, 'pigeon keeper's lung' often occurs in individuals with HLA-A1.8, suggesting the existence of an immune response gene associated with the tissue compatibility antigen system.

　　1. Serum sickness:It refers to an immune complex disease that occurs as a complication of injection with exercise immune serum, and its main manifestations include rash, fever, joint pain, lymphadenopathy, etc.

　　2. Vasculitis:It is characterized by inflammatory cell infiltration in the vascular wall and around the blood vessels, accompanied by vascular injury, including fibrin deposition, collagen fiber degeneration, necrosis of endothelial cells and muscle cells, also known as vasculitis.

　　1. Completely avoiding contact with pathogenic organic dust is the most fundamental preventive and control measure.

　　2. Improve the production environment, pay attention to dust prevention, ventilation, and strictly follow operational procedures, such as drying the hay and grain after harvesting before storing them in the barn.

　　3. Keep the places where poultry are raised clean and properly dispose of bird droppings.

　　4. Keep the water in humidifiers and air conditioning systems clean to avoid contamination. Those working in environments polluted with organic dust should undergo regular medical surveillance.

　　Those with obvious chronic respiratory diseases such as chronic asthmatic bronchitis, bronchial asthma, chronic obstructive pulmonary emphysema, and those with allergic constitution should not engage in jobs that require close contact with organic dust.

　　1. Routine laboratory tests:Routine laboratory tests have little diagnostic significance. During acute attacks, peripheral blood counts show an increase in white blood cells (15～25)×109/L, accompanied by an increase in neutrophils, but rarely an increase in eosinophils.

　　2. Immunological examination:It can be used for the detection of simple Ouchterlony biphasic gel diffusion technology, and the presence of specific precipitins IgG in the serum is helpful for diagnosis. However, those who are asymptomatic due to extensive exposure to allergens can also have precipitating antibodies against specific antigens. Gamma globulin can increase to 20～30g/L, accompanied by elevated levels of IgG, IgM, and IgA, normal IgE levels, normal serum complement, and positive rheumatoid factor.

　　3. Chest X-ray:The findings vary depending on the type of disease, with the acute type often showing diffuse small granulomatous infiltration of alveoli or interstitial pneumonia, and also small nodular precipitates. In chronic cases, the infiltrates merge together, and X-ray changes are generally absorbed within 3-6 months, but severe cases may persist.

　　4. Pulmonary function tests:Pulmonary function tests show restrictive ventilation impairment, dysfunction, including low vital capacity, reduced lung compliance, decreased diffusion capacity, no obvious airway obstruction and increased vascular resistance, local mismatch of ventilation and blood flow ratio, and decreased arterial oxygen saturation, which is more obvious during exercise.

　　Patients often have water, electrolyte, and acid-base imbalance in their bodies, so they should eat some foods rich in iron, such as animal livers and yolks; foods high in copper, such as beef liver, sesame paste, pork, etc.; and also high-calcium foods such as shrimp shells and dairy products:

　　1. Eat less cold and cool fruits, as they can damage the Yang of the spleen and stomach, hinder the function of transformation and transportation, and are not conducive to the recovery of the disease. Apples should be eaten in moderation and selected in the diet of pneumonia.

　　2. It is advisable to avoid spicy and greasy foods, as pneumonia is an acute febrile disease that consumes the body's vital energy, affects the function of the internal organs, and is prone to reduce digestive function.

　　1. The best way to terminate an acute attack is to avoid allergens and simultaneously apply glucocorticoid therapy (Prednisone 30-60mg/d, medication for 1-2 weeks). For cases with chronic fibrosis, the efficacy of glucocorticoids is poor.

　　2. For severe attacks, adrenocorticosteroids can be administered, but the specific dose and treatment duration have not yet been concluded. Most scholars give prednisone (Prednisone) orally, starting with a daily dose of 40-60mg, and gradually reducing the dose after 2 weeks, with a total course of 4-6 months. Prednisone (Prednisone) can reduce the duration of the acute phase and mortality, but cannot prevent the occurrence of chronic EAA. Small-dose hormone therapy can also be given to patients with chronic EAA, but the clinical effects vary greatly.