Hypersensitivity pneumonitis

Introduction to allergic pneumonia Hypersensitivity pneumonitis (hypersensitivity pneumonitis) is a group of non-asthmatic allergic lung diseases caused by different allergens, with diffuse interstitial inflammation as its pathological feature. Exogenous allergic alveolitis (extrinsicalleralicalveolitis) is also called an allergic reaction caused by the inhalation of organic dust particles (diameter <10) containing fungal spores, bacterial products, animal proteins or insect antigens. basic knowledge The proportion of illness: 0.02% Susceptible people: no specific population Mode of infection: non-infectious Complications: honeycomb lung syndrome

Cause of allergic pneumonia

It is a group of non-asthmatic allergic lung diseases caused by different allergens, with diffuse interstitial inflammation as its pathological feature. It is an allergic reaction caused by inhalation of organic dust particles (diameter <10) containing fungal spores, bacterial products, animal proteins or insect antigens.

Allergic pneumonia prevention

Avoiding the inhalation of antigens is the best preventive measure. Farmers need to wait until they are dried and put them into the warehouse to prevent mold, raise poultry, pigeons and all kinds of birds. Keep the shed clean and treat the feces and fallen feathers in time. Wear protective masks when working, humidifiers and air conditioners should be cleaned frequently to prevent mold or other contamination.

Allergic pneumonia complications Complications, cellular lung syndrome

Cellular lungs appear in the late stage.

Symptoms of allergic pneumonia Common symptoms Difficulty breathing, loss of appetite, dry cough, allergic cough, no wheezing, phlegm, short cough, wheezing

Symptoms appear after a few hours of exposure to the antigen: fever, dry cough, difficulty breathing, chest pain, and purpura. A small number of atopic patients may have an allergic reaction such as wheezing and salivation after exposure to the antigen, and a type III reaction after 4 to 6 hours is an allergic pneumonia. Physical examination showed a wet rales in the lungs, no wheezing, no physical or airway obstruction. X-ray films showed diffuse interstitial infiltration, and miliary or nodular shadows, which were more pronounced in the middle and bottom of the lungs and later expanded into patchy dense shadows.

In acute attacks, peripheral blood cells showed an increase in white blood cells of 15 × 10 ⁹ ~ 25 × 10 ⁹ / L (15000 ~ 25000) with increased neutrophils, but more eosinophils increased, gamma globulin increased to 20 ~ 30g / L (2 ~ 3g / dl), with elevated IgG, IgM and IgA, normal serum complement, rheumatoid factor can be positive. Pulmonary function tests showed that the restrictive ventilatory disorder had decreased lung capacity, decreased diffusible energy, imbalanced local ventilatory blood flow, no significant airway obstruction and increased vascular resistance.

Examination of allergic pneumonia

1. Pulmonary function test: Pulmonary function test is a very useful means for estimating the degree of lung damage. It can also be used as an observational treatment effect, acute and subacute hypersensitivity pneumonitis, lung capacity reduction, forced vital capacity (FVC), and force in the first second. Expiratory volume (FEV1), total lung volume (TLC), and lung compliance (CL) were all reduced, and the 1 second rate was always normal. It was a restrictive ventilation disorder, and the general lung function changes were consistent with extensive bronchiole obstruction. The above examination is best performed within 4 to 8 hours after the onset, because it can return to normal after 12 to 24 hours, blood gas analysis, blood oxygen saturation, oxygen partial pressure, carbon dioxide partial pressure, etc. have slight changes, chronic phase FVC, TLC, DLCO, PaO2, SaO2 decreased, serum can be detected in allergen precipitation antibodies, farmers lung, mushroom lung, sugarcane pneumoconiosis, pigeons can detect the corresponding antibodies, 40% of asymptomatic antigen contacts The corresponding precipitated antibodies, precipitated antibodies only represent exposure to such antigens.

2, inhalation challenge test: with the antigen extract inhalation, a positive reaction can occur within a few hours, manifested as fever, cough, shortness of breath, objective indicators of pulmonary dysfunction, FEV1 decreased, and sometimes bronchospasm, The positive reaction is helpful to find out the original allergic reaction. It has been confirmed that certain antigens or serum have been detected with specific precipitated antibodies. The lung function is obviously reduced and the severe patients are not suitable for the stimulation test.

3, skin allergy test: skin allergy test positive reaction, and there are false positives, it is not suitable as a basis for diagnosis of disease.

4, bronchoalveolar lavage has a certain diagnosis: normal non-smokers alveolar lavage fluid (BALF) in macrophages accounted for 85% to 90%, lymphocytes accounted for 6% to 10%, neutrophils in 1 %~2% or less, but allergic pneumonia increased first with neutrophils within 24h, followed by lymphocytosis, the total number of cells in BALF is 3 to 5 times normal, of which lymphocytes account for 60%, mainly T Lymphocytes, B lymphocytes account for a small number, of which suppressive T cells (CD8) predominate, so the ratio of CD4/CD8 is inverted, the immunoglobulin in BALF increases, the main IgG, IgA increase, 4 times higher than the asymptomatic, acute phase The white blood cells in the patient's blood occasionally move left, the total number is not high, and the eosinophils in the blood rarely rise.

Acute early chest X-rays may not show obvious abnormalities. It has been reported that pathological biopsy confirmed allergic pneumonia but the chest X-ray is completely normal. Another 26 cases of typical clinical symptoms of mushroom lung only 8 cases showed chest X-ray abnormalities, another report Of the 107 peasant lungs, 99 (93%) had diffuse lung shadows on the chest X-ray. The degree of shadow was not necessarily parallel with lung function, BAL, and clinical symptoms. The chest X-ray showed mostly nodules with two lungs. The diameter of the nodules varies from 1 mm to several millimeters, the boundary is unclear, or the glass is shaded, and some of the shadows are reticulated or net nodular. The lesions have no special tendency but the cusps and base segments. Less, fine mesh and nodular type are mostly subacute performance, Fraser et al. have seen peasant lungs, mushroom lungs and pigeons in the lungs. In the acute phase, alveolar shadows are common in short periods of time after exposure to severe antigens. Alveolar-like shadows are often small airway occlusions of bronchiolitis obliterans, images of increased density of contents in the alveoli, persistent persistence of diffuse reticular or reticular nodular shadows, and acute exacerbations Acinar-like shadows.

In allergic alveolitis, the lungs of the mushroom have hilar and mediastinal lymph nodes, and individual peasant lungs also have lymphadenopathy.

Chest X-rays often have flaky shadows that may represent consolidation of the alveoli, and thickening of the interlobular septa at the rib crypts may represent a high load of lymphatic drainage.

The patient is out of contact with the allergen within 10 days to several weeks, and the shadow of the chest X-ray can be resolved to return to normal. The prognosis depends on the frequency of contact with the allergen and the duration of the severity of the exposure. The key is early diagnosis and In the absence of allergens, the diffuse nodules in the acute or subacute phase are replaced by diffuse interstitial fibrosis, which becomes a medium or coarse reticular and net nodular shadow. When the honeycomb lesion occurs, the lung volume can be reduced and scar formation is formed. Atelectasis, and unaccompanied lungs form compensatory emphysema. Such cases are difficult to recover from disengagement and active treatment. Hargreave reported that in 20 cases of pigeons, 20 patients had leaf systolic atelectasis and 17 lungs. Involution occurs in the upper lobe, and patients with advanced ring have a ring shadow diameter of 5 to 8 mm. Some parts are honeycomb lungs, which tend to be distributed in the upper lobe. It is sometimes difficult to distinguish between late hypersensitivity pneumonitis and idiopathic pulmonary fibrosis.

The diagnosis of most patients should be based on clinical manifestations, because chest X-ray abnormalities are only a few, but a few patients with chest X-ray findings fully consistent with the performance of allergic pneumonia without any clinical symptoms.

High-resolution tomography (HRCT) is one of the main methods for diagnosing allergic pneumonia. Early hypersensitivity pneumonitis with chest X-ray examination of HRCT can detect early pulmonary interstitial lesions. HRCT can find some important features, such as in the lungs. There is a cystic light-transmitting area between the medulla and the cortex in the diffuse net nodules or frosted glass. It is considered to be a characteristic of allergic pneumonia caused by allergic pneumonia with obliterative bronchiolitis. Allergic pneumonia Another feature is that there is a part of normal lung tissue between the shadows, interspersed between ground glass or nodules and reticular shadows. These two manifestations can only be found by HRCT. These changes are often CT or chest radiographs. Covered by the effect, the HRCT performance is as follows:

1, on both sides or on one side of the sheet, nodules or mesh shadows.

2. Grinding glassy shadows.

3. The above two shadow cystic light transmissive areas or normal lung tissue have reference value for the diagnosis of this disease.

4, the performance of pulmonary interstitial fibrosis, late stage may have a honeycomb lung.

Diagnosis and diagnosis of allergic pneumonia

diagnosis

Because the incidence of this pneumonia is not high, the first episode is often confused with other pneumonia, but if you carefully analyze the characteristics of the medical history, including environmental factors, such as the existence of straw containing fungi in the living environment of the child, it is susceptible Allergic pneumonia, so this pneumonia is called "peasant lung", such as feeding pigeons at home, allergic pneumonia caused by animal protein allergy in pigeon dung is called "feeding pigeon lung", the diagnosis is mainly based on antigen Contact history, clinical symptoms, signs, chest X-ray, combined with serological examination of precipitated antibodies and bronchoalveolar lavage, etc., some cases are difficult to diagnose, misdiagnosed as it, often through repeated attacks to find allergens, individual Affective diagnosis by inhalation stimulation test, a small number of patients need to do lung biopsy, with special environmental factors, combined with the child's symptoms, signs and lung function changes, chest X-ray film, and allergen examination and other diagnosis is not difficult.

Differential diagnosis

The acute phase of the disease should be differentiated from viral lung infection, bronchial asthma, pulmonary eosinophilic lung infiltration, allergic bronchopulmonary aspergillosis, pulmonary edema caused by chemical agents, and chronic phase should be associated with idiopathic pulmonary fibrosis. Phase III patients were identified. In addition, it needs to be differentiated from invasive tuberculosis, lung cancer, and viral pneumonia.

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