Hypersensitivity pneumonitis

　　Allergic pneumonia is a group of non-asthmatic allergic pulmonary diseases caused by different allergens, with a low incidence in children. The allergens are organic dust particles containing fungal spores, bacterial products, animal proteins, or insect antigens. According to statistics, there are currently at least 40 known organic dust antigens that can cause allergic pneumonia.

　　The occurrence of allergic pneumonia is mainly due to organic dust as an immunogen. Its particles should be less than 5 to 6 μm. Because particles larger than this diameter are mostly deposited in the upper respiratory tract or large bronchi, only when the reactants enter the small airways and alveoli and enter the surrounding lung tissue can they cause alveolitis. When the reactive particles in the alveoli reach a certain amount, the lung tissue produces a strong immune response, causing allergic alveolitis.

　　Late-stage allergic pneumonia patients may develop honeycomb lung. Honeycomb lung is a pulmonary change characterized by a honeycomb-like appearance formed by various late-stage lung diseases. The lesions often involve the middle and lower lung fields, forming cysts with a diameter of about 1 cm, arranged one by one, resembling a honeycomb or beehive. Symptoms include pulmonary function failure, manifested as decreased gas exchange function, hypoxia, and asphyxia. X-ray manifestations show thickening and disorder of pulmonary vessels,呈线状、条索状 or multiple annular lucency. Due to the shrinkage of the lower lung lobe, the intercostal space often becomes narrow and the diaphragm rises, which may be accompanied by displacement of the mediastinum, trachea, or hilum.

　　After inhaling allergens, a few children with allergic pneumonia may show prodromal symptoms such as wheezing and runny nose. Symptoms start to appear 3 to 6 hours later,表现为 fever, dry cough, rapid breathing, chest pain, and hypoxia, as well as cyanosis of the lips, fingertips, and toes. The above symptoms reach their peak within 6 to 8 hours, and the symptoms are basically gone within 24 hours. During the attack, the physical signs of the lungs are different from those during asthma attacks, with few wheezing sounds, and mainly wet rales are heard.

　　Acute type usually develops within 4 to 8 hours after contact with the antigen, with symptoms such as fever, aversion to cold, cough, and difficulty breathing. Nausea, vomiting, and anorexia may also occur. Auscultation of the lungs shows fine to moderate inspiratory wet rales, and wheezing sounds are uncommon. After withdrawal from the antigen, symptoms generally improve within a few hours, but complete recovery may take several weeks, and recurrent episodes can lead to pulmonary fibrosis. Subacute cases may present with asymptomatic onset, with cough and difficulty breathing lasting for several days to several weeks, and patients with progressive disease may require hospitalization. Chronic type may lead to dyspnea, cough, fatigue, and weight loss for several months to several years after progressive activity, and severe cases may develop respiratory failure.

　　Summer is the peak period for allergic pneumonia because the air is relatively dry and turbid in summer. Nowadays, air pollution is serious, and people living in such an environment for a long time are prone to upper respiratory tract diseases, among which allergic pneumonia is a common one.

　　1. The most fundamental preventive and treatment measure for allergic pneumonia in summer is to prevent and treat early, and to leave the environment of allergens early. If the influence of allergens can be eliminated in time, the symptoms such as fever, cough, and shortness of breath can all disappear within a week.

　　2. The best preventive measure for allergic pneumonia in summer is to prevent and treat early, and to leave the environment of allergens early. If the influence of allergens can be eliminated in time, the symptoms such as fever, cough, and shortness of breath can all disappear within a week.

　　3. It is necessary to strengthen indoor ventilation and air exchange, regulate the environment, to reduce the invasion of allergens into the respiratory tract.

　　4. Patients with fever can use alcohol baths and other physical methods to lower body temperature, and coughing patients can use cough suppressants for symptomatic treatment. In addition, corticosteroids and aminophylline have certain curative effects on the disease, while the use of antibiotics is of no help.

　　5. At the same time, it can be配合使用antiallergic drugs, which can have a good effect.

　　5. Patients should eat warm, light, and soft foods, and can eat less and more often. Eat more fruits, vegetables, beans, and high-fiber foods, and avoid allergenic and irritant foods such as fish, shrimp, chili, strong tea, coffee, and alcohol.

　　Although it was previously believed that the presence of positive serum precipitating antibodies could be used to make a definite diagnosis of allergic pneumonia, the existence of serum antibodies is neither sensitive nor specific. The diagnosis is based on a history of environmental exposure, relevant clinical characteristics, chest X-ray, pulmonary function tests, and fiberoptic bronchoscopy. The history of exposure can provide clues (such as people who have been exposed to antigens at work may be asymptomatic, or symptoms may reappear within 48 hours after re-exposure). The history of exposure to pathogenic antigens is not easy to find out, especially 'air conditioning lung' (humidifier lung). Environmental investigations by experts for difficult cases are helpful for diagnosis. For patients who are difficult to conclude or have no history of environmental exposure, lung biopsy can be performed.

　　1. Imaging

　　The chest X-ray examination may be normal or show diffuse interstitial fibrosis. Bilateral plaques or nodular infiltrates often appear, with thickened bronchopulmonary markings, or small acinar changes, suggesting pulmonary edema. Lymphadenopathy at the hilum and pleural effusion are rare. CT, especially high-resolution CT, is of high value in judging the type and extent of the lesions.

　　(1) The CT manifestations of acute allergic pneumonia show bilateral ground-glass changes; widespread patchy, mass-like, and fluffy pulmonary consolidation shadows, with blurred edges, uneven density and distribution, more common in the middle and lower lungs. The location of the lesions changes greatly and is migratory in a short period of time. The pathological basis of the imaging manifestations of acute allergic pneumonia is the infiltration of neutrophils and eosinophils in the lung parenchyma and inflammation of small blood vessels, leading to diffuse pulmonary congestion and edema, as well as the exudation of protein fluid in the alveoli.

　　(2) The CT manifestations of subacute allergic pneumonia show diffuse distribution of small lobular central nodular shadows, with unclear edges; patchy ground-glass shadows; gas trapping sign and lung cystic change. The pathological basis of imaging manifestations of subacute allergic pneumonia: the small lobular central nodular shadow is the manifestation of cellular bronchitis; the ground-glass shadow is the manifestation of diffuse lymphocytic interstitial pneumonia; gas trapping sign and lung cystic change are the result of bronchitis, obstruction. The small lobular central nodular shadow and ground-glass change are characteristic changes of allergic pneumonia, and the small lobular central nodular shadow is the characteristic change of subacute allergic pneumonia.

　　(3) The CT manifestations of chronic allergic pneumonia show reticular and honeycomb-like fibrous strip shadows, indicating pulmonary interstitial fibrosis; in severe cases, atelectasis, emphysema, and pleural thickening can be seen. The pathological basis of imaging manifestations of subacute allergic pneumonia: the reticular shadow is the manifestation of cellular bronchitis; the ground-glass shadow is the manifestation of diffuse lymphocytic interstitial pneumonia; gas trapping sign and lung cystic change are the result of bronchitis, obstruction.

　　2. Pulmonary function

　　It is mostly restrictive, with reduced lung volume, decreased carbon monoxide diffusion, abnormal ventilation/perfusion ratio, and hypoxemia. Obstruction of the airway is not common in acute cases, but it can occur in chronic cases. Eosinophils are normal.

　　3. Bronchoscopy

　　Bronchoalveolar lavage is a sensitive method to determine the presence or absence of alveolitis. Generally, it can be seen that lymphocytes, especially T cells increase, with CD8+ (cytotoxic inhibitory) T cell subset as the main. The value of bronchoscope biopsy is very limited, as the sample is too small, it can cause misdiagnosis.

　　Patients with allergic pneumonia should eat more fresh fruits and vegetables, eat more foods rich in vitamin C, such as oranges, strawberries, kiwis, etc., and eat more foods rich in vitamin A, such as fatty fish and eggs, which is very important for maintaining the health of the tracheal membrane. Avoid eating foods with high sugar content, high-protein diet, spicy foods, etc. Allergic pneumonia food therapy (the following information is for reference only, detailed information needs to be consulted with a doctor):

　　1. Jasmine Tofu Soup: 120 grams of fresh jasmine root, 250 grams of tofu. Put the fresh jasmine root and tofu into a pot, add water, and boil.

　　2. Pumpkin Beef Soup: 250 grams of lean beef, 6 grams of ginger. Boil the beef with water until it is eight degrees done, add 500 grams of peeled pumpkin, and cook together until done, season with salt and monosodium glutamate.

　　3. Chrysanthemum Leaf Honey Drink: 150 grams of chrysanthemum leaves, 30 grams of honey. Cut the chrysanthemum leaves into pieces, add water to boil for 10 minutes, filter the residue to get the juice, add honey, and boil for a moment. Take one dose per day, divide it into three servings, and drink it for 5 consecutive doses.

　　4. Honeyed Radish: 250 grams of white radish, 3 tablespoons of molasses. Peel the white radish, slice it, put it in a bowl, add 3 tablespoons of molasses, mix well, and leave it overnight.

　　5. Silver and Mung Bean Porridge: 30 grams of silver dew, 50 grams of mung beans, 150 grams of glutinous rice, 15 grams of dried tangerine peel, 25 grams of fresh lotus leaf, 20 grams of fresh bamboo leaf, and appropriate amount of sugar. Cut the lotus leaf, bamboo leaf, and dried tangerine peel into pieces, add water to boil for 10 minutes, and filter the residue to get the juice. Put the mung beans and glutinous rice into a pot, add water, boil with strong fire, then cook with low fire until done, add silver flower dew, medicine juice, and sugar, and boil for a moment. Take one dose per day, divide it into two servings, and take it for 5 consecutive doses.

　　6, Fish grass mustard green tea: 50 grams of fish grass, an appropriate amount of sugar. Boil the fish grass and mustard green with water for 10 minutes, strain the juice and add sugar.

　　7, Chestnut braised pork: 250 grams of chestnuts, 500 grams of lean pork, a little salt, ginger, and soybean paste. Peel the chestnuts, cut the pork into pieces, add salt and other seasonings, add an appropriate amount of water, and braise until cooked.

　　8, Yam lily soup: 200 grams of yam, 50 grams of lily. Put the two ingredients in a pot, add 5 bowls of water, boil to 3 bowls, take three times a day, finish one day.

　　9, Fish grass egg: one handful of fish grass, several eggs. Boil and eat the egg bag for several days to recover.

　　The treatment of allergic pneumonia first requires the removal of allergens. Acute attacks can resolve naturally, and symptomatic treatment should be given to those with significant symptoms. If symptoms persist and worsen with cyanosis, oxygen should be administered and prednisone 30-60mg/d should be given, with a maintenance dose of 20-30mg/d after the condition stabilizes. The dose should be reduced and gradually discontinued after the symptoms completely disappear. Chest HRCT lesions that appear as ground-glass opacities usually improve after glucocorticoid therapy. When most of the shadows are honeycomb-like, the efficacy of glucocorticoid therapy is poor.

　　Early diagnosis and avoidance of antigens are the key to treatment. Removing allergenic antigens from the patient's contact environment is crucial for both treatment and prevention. Drug therapy has an important auxiliary role in only a few cases. Glucocorticoid therapy can alleviate and eliminate symptoms during the acute exacerbation phase and can prevent permanent damage such as bronchial dilation, irreversible airway obstruction, and pulmonary fibrosis. For patients with mild lung function impairment who can recover spontaneously by avoiding antigen contact, hormone therapy is not required. Patients with more severe conditions may use prednisone. The lung function should be dynamically observed for the first four weeks of treatment, and the dosage of hormones should be gradually reduced after objective indicators improve, until discontinuation. Cell毒性 drugs such as cyclophosphamide, cyclosporine, and azathioprine can be used for refractory, progressive allergic pneumonia, but there is insufficient research on their efficacy.