Acute interstitial pneumonia

Introduction to acute interstitial pneumonia Acute Interstitial Pneumonia (AIP) is a rare and rapidly developing fulminant lung injury. AIP has a sharp onset (within days to weeks), with fever, cough and shortness of breath, followed by respiratory failure. The average age of onset was 49 years, and there was no significant gender difference. Routine laboratory tests are not specific. The mortality rate of AIP is extremely high (>60%), and most of them die within 1 to 2 months. basic knowledge The proportion of the disease: more common, the incidence rate in respiratory diseases is about 5% -10% Susceptible people: no specific population Mode of infection: non-infectious Complications: spontaneous pneumothorax

Cause of acute interstitial pneumonia

(1) Causes of the disease

Although it has been classified as idiopathic interstitial pneumonia (IIP), its clinical manifestations and pathological manifestations are almost identical to those of ARDS, and there is no clear cause of its onset, so some people think that its onset and virus Acute infection is closely related. It is only limited to the current detection technology. The relationship between virus and IIP has always been one of the hotspots of the etiology of the disease. The most studied are adenovirus and Epstein-Barr virus.

(two) pathogenesis

It is now preliminarily believed that the role of the virus in IIP development may be as follows: 1. The viral protein expressed by human cells infected with the virus can promote chronic inflammation and repair processes, such as the recessive membrane protein of Epstein-Barr virus. Increase the expression of class II antigen of B-lymphocytes; 2 virus infection can activate type I collagen gene of alveolar epithelial cells; 3 virus gene is an activating factor that can bind or contact DNA to regulate RNA protein transcription and Modifying the biological characteristics of cells, unfortunately, these findings are all from the chronic type of IIP; perhaps because of the small number of cases, there has been no research report on the relationship between AIP and virus.

Studies have reported that some patients have autoantibodies in peripheral lymphocytes, lymphoid follicles and plasma cells, and immune complexes are deposited on the alveolar wall, such as ESR, some patients have increased gamma globulin, and anti-nuclear antibody titers rise. Rheumatoid factor, cold immunoglobulin, lupus cell positive, and decreased complement levels indicate that the disease may be related to the inflammatory immune process. It has also been reported that the disease may have genetic factors.

Acute lung injury in AIP is more prone to a wide range of lung changes - acute respiratory failure; it is quite different from the acute injury-recurring multifocal injury seen in other IIP types, this difference Both of them have their own characteristics in histopathology and clinical manifestations; and it is speculated that the pathogenesis of the two is also different. Although the current research has reached the level of protein and even genes, such as pro-inflammatory factors and anti-inflammatory factors are known. The corresponding role of metalloproteinases and inhibitors and apoptosis in IIP, but the exact pathogenesis of AIP is still unclear.

Pathology showed that the lungs were dark red, the weight increased, the appearance was full, the texture was firm and hard, the touch pressure did not collapse, the lung cut surface was dark red spots and grayish white, and there were staggered gray fiber tissue lines and small focal points. Scar tissue, light microscopy: early (exudative) lesions (about 1 week after lung injury), alveolar septum due to vasodilatation, matrix edema and inflammatory cell infiltration and diffuse thickening, which is mainly lymphocyte infiltration There are also plasma cells, mononuclear (or macrophages), neutral and eosinophils and a few fibroblasts; alveolar epithelial hyperplasia and metaplasia form a column, widening the alveolar septum; normal or a small amount of protein inside the alveolar space Sexual substances and cell exudation, the alveolar septum at this time is relatively thin, the alveolar structure is still normal, and the response to treatment is good. As the disease progresses, the vascular endothelium and alveolar epithelial cells are damaged, necrotic and shedding; the alveolar cavity is evenly formed. Powdered eosinophils - transparent membranes, about 2 weeks, DAD enters late (proliferation or mechanization), alveolar septa appear extensively proliferating fibroblasts and myofibroblasts, while collagen deposition is less This makes the alveolar space significantly widened; the capillaries are replaced by fibrous tissue and the number is reduced; the intimal hyperplasia of the pulmonary arterioles, the thickening of the wall, and sometimes the mechanized emboli in the small and medium pulmonary arteries; the alveolar fibrosis and atresia Decreased, the residual alveoli are irregular in shape, vary in size, or have a fissure or abnormal expansion. Due to the necrosis of type I alveolar epithelial cells, type II epithelial cells proliferate in a columnar or stud-like arrangement, lining the alveolar surface; There are a number of bronchial epithelial cells in the UIP that are involved in the distribution on the alveolar surface. In addition, squamous metaplasia can occur in the respiratory bronchiole epithelium, and the honeycomb lung can appear several weeks later.

Electron microscopy: loss of type I alveolar epithelial cells, local or even large area of alveolar epithelial cell basement membrane exfoliation, cytoplasmic edema and necrosis of type II alveolar epithelial cells and capillary endothelial cells, cell debris and fibrin, red blood cells and surface activity A mixture of substances is distributed along the surface of the alveoli, especially in the transparent membrane formation area under the microscope, scattered inflammatory cells, especially macrophages, lymphoid and plasma cells are present in the alveolar space; and the interstitial edema matrix and different A large number of fibroblasts, a small amount of inflammatory cells and scattered primitive parenchyma cells are distributed around the amount of collagen and elastic fibers. Further studies have found that the presence of a large number of fibroblasts and a small amount of collagen in the interstitial is not the only cause of interstitial thickening. The reason is that most of the alveolar cells have different degrees of collapse due to the exfoliation of the basal layer of alveolar epithelial cells. Another feature of this collapse is that in the collapsed alveolar part, there are many adjacent epithelial cell base layers overlapping and folding each other. a structure consisting of a two-layered basal layer inserted into the alveolar wall in a limp manner, at intervals Deep fissures are formed inside. When type II alveolar epithelial cells are re-epithelialized along the exfoliated basal layer, the cells do not penetrate deep into the fissures, but cover the two outer sides of the fissures, and if the alveoli are completely collapsed, they are separated from each other. The alveolar septum also folds at this time. When the type II alveolar epithelial cells re-grow, it does not directly grow on the surface of the detached basal layer. There is a layer of residual inflammation between the epithelial cells and the basal layer. The result of the two phenomena in the alveolar cavity is that when the type II alveolar epithelial cells proliferate to cover the detached epithelial basal layer, the cells are covered by the collapsed part rather than re-line along the intact basal layer. Arrange and re-expand the alveoli; because a layer of partially overlapping alveolar walls incorporates a single thickened alveolar septum, plus the "infiltration interval" of exudate in the alveolar cavity in some areas, which is combined with other factors Interstitial fibrosis seen under the microscope.

Acute interstitial pneumonia prevention

Prevention of bacterial infections is particularly important due to the use of large amounts of glucocorticoids.

Acute interstitial pneumonia Complications spontaneous pneumothorax

Spontaneous pneumothorax and right heart dysfunction.

Symptoms of acute interstitial pneumonia Common symptoms Respiratory failure, dyspnea, dry cough, purulent chest, chest tightness, or bandage, fatigue, chest tightness, cyanosis, retention of respiratory failure

AIP is sudden onset, rapid progress, rapid respiratory failure, maintenance of mechanical ventilation, average survival time is short, most of them die within 1 to 2 months, there is no gender difference in the incidence of AIP, the age range of onset in the literature It is 7 to 83 years old, with an average age of 49 years. Most patients have physical health and sudden onset; most patients have symptoms similar to upper respiratory virus infection in the early stage of onset, which can last from 1 day to several weeks, although extensively studied. No evidence of viral infection, more than half of the patients have sudden fever, dry cough, secondary infection may have purulent sputum; chest tightness, fatigue, with progressive aggravation of breathing difficulties, may have cyanosis, wheezing, chest tightness or belt sensation The clubbing (toe) appears very quickly, and the cracks can be heard at the bottom of the lungs. Some patients may have spontaneous pneumothorax, antibiotic treatment is ineffective, and died of acute respiratory failure and right heart failure more than 2 weeks to 6 months. If the glucocorticoid is applied in sufficient amount in the early stage, the condition can be alleviated or even healed.

Examination of acute interstitial pneumonia

Laboratory tests are not specific; peripheral blood leukocytes can be increased, a small number of eosinophils are slightly increased, red blood cells and hemoglobin are increased secondary to hypoxia, and erythrocyte sedimentation rate is accelerated, up to 60 mm/h, and serum protein electrophoresis shows 2 Or gamma globulin increased, IgG and IgM often increased, IgA increased less; blood gas analysis for type I respiratory failure, occasionally type II.

The imaging performance of AIP is not much different from ARDS, or it is not specific. In the early stage, some patients' chest radiographs can be normal; most of them are scattered or extensive patchy, patchy in the lower lungs. Shadow, at this time and bronchial pneumonia is not easy to identify, as the disease progresses progressively, the lungs appear asymmetric diffuse reticular, strip-like and spotted infiltrative shadows, and gradually extend to the upper middle lung field, especially The band is obvious; but the lung tip lesion is rare, the hilar lymph node is not large; occasionally pneumothorax, pleural effusion and pleural thickening, chest CT is mostly thickened lung texture, structural disorder, small piece of shadow and visible bronchiectasis There are also frosted glass-like changes on both sides of the edge, or bilaterally distributed linear, reticular, small nodular or even solid shadows, occasionally small honeycomb-like images, Ichikado et al. summarized 14 cases of AIP (3 cases) The relationship between the pathological findings of open lung biopsy and 11 cases of autopsy was related to HRCT. He first divided the pathological manifestations of the lung into acute exudation, subacute proliferation and chronic fibrosis, which respectively represented the presence of the following: transparent membrane, Edema, exudation or hemorrhage in the vesicle; type II alveolar epithelial cells proliferate, fibroblasts proliferate in the interstitial and alveolar spaces; a large number of fibroblasts and collagen connective tissue proliferate and intracellular changes in the lungs, followed by HRCT techniques, Comparing the relationship between pathological staging and imaging findings, he found that:

1 During the exudation period, some residual normal lung tissue images are close to the shadow area [referring to the glassy and/or solid area] or exist in the shadow area; no matter what the shadow is, it is not accompanied by The appearance of bronchiectasis images.

2 In the proliferative phase, the incidence of bronchiectasis in the ground-glass and metamorphic areas is almost the same.

3 In the fibrosis stage, almost all of the lung shadow areas were accompanied by the appearance of bronchiectasis, and one patient was found to have small cell-like changes. From the analysis of this result, we can see that HRCT does not diagnose AIP. Specificity, imaging performance can not be as well delineated as pathological manifestations; but the emergence of bronchial traction expansion images indicates that the exudation period will be full and some degree of mechanization has emerged, but no matter what, It is still beneficial to have a timely HRCT examination of patients suspected of having AIP, at least for the sampling site that guides the open lung biopsy, as early as possible to obtain the correct diagnosis and timely treatment.

Akira compared the CT changes in the acute exacerbation of AIP and IIP. He found that AIP patients never had imaging findings of subpleural hyalinization, and only after 7 days, bronchial stretch expansion and honeycomb lungs gradually appeared. In the acute exacerbation of IIP, bilateral diffuse or multiple focal vitreous changes and subpleural honeycomb-like changes can be seen.

Diagnosis and diagnosis of acute interstitial pneumonia

The disease does not have specific clinical diagnostic indicators, so the most important thing is to think about the possibility of the disease, and then should be identified between AIP and ARDS, the latter often have a clear incentive, while the former is more difficult to find If you want to confirm the diagnosis, you have to rely on clinical diagnosis and lung biopsy, especially open lung biopsy.

Differential diagnosis

Interstitial pneumonia

Including UIP, DIP and NSIP, their common features are more insidious onset, longer course, more patients with progressive chest tightness, shortness of breath, visible CT or reticular shadow on chest CT, subpleural arcuate line shadow and bronchus Expansion; Tianshan Yaxing has reported that all of these patients have radiographic images of varying degrees in imaging. The common feature of histology is that mature fibrotic cells are mostly mature collagen fibers, while activated fibroblasts rarely appear. Not even, this is exactly the opposite of AIP's performance. The specific pathological manifestations of a certain type are described below.

(1) UIP: Its biggest feature is: when converting low-power field of view, normal lung tissue, interstitial fibrosis, inflammatory cell infiltration and honeycomb-like changes are under the microscope, most of the fibrous tissue consists of a large amount of eosinophilic collagen and A small amount of corresponding inflammation or stromal cell composition, collagen deposition thickens the alveolar wall and forms flaky traces or changes with honeycomb-like changes. In the enlarged honeycomb cavity, bronchial epithelial cells or proliferating type II alveolar epithelial cells are covered. The surface of the air cavity; the air cavity contains concentrated mucus tissue, neutrophils and other inflammatory cells. The alveoli are separated by thickened alveolar walls caused by collagen and different numbers of chronic inflammatory cells, although most of them The fibrotic area is composed of acellular tissue-free collagen tissue which reveals the oldness of fibrosis; however, in some areas there is an accumulation of activated fibroblasts, which indicates that fibrosis is still active; The appearance of this "new and old" fibrosis at the same time in the specimen is the key to the diagnosis of UIP. In the whole specimen, the inflammatory response is usually only moderate, mainly lymphocytes. Primary, followed by macrophages and neutrophils, these inflammatory cells mainly appear in areas of collagen deposition or honeycomb-like changes, which is related to the unexplained chronic inflammation caused by chronic inflammation, which is IIP, especially UIP. The hypothesis of the pathogenesis is consistent. For the occasional acute exacerbation of UIP cases, in addition to pathological manifestations, clinical manifestations are also a powerful means of identification.

(2) DIP: The biggest feature is that a large number of macrophages accumulate in the alveolar space, just like a large number of alveolar epithelial cells fall off, hence the name. In fact, these cells are mostly mononuclear cells, and a small number of scattered multinucleated giant cells exist, alveoli The alveolar epithelial cells on the wall showed a hyperplastic form. The alveolar septa was light and moderately widened due to collagen deposition and infiltration of a small amount of inflammatory cells. Under low magnification, the performance of DIP was very simple, not only the absence of fibrils. Cellular aggregation, cell-like changes are also rare; this is in sharp contrast to the histological features of UIP.

(3) NSIP: The degree of inflammation and fibrosis in the alveolar wall varies greatly, lacking the specific indications for the diagnosis of UIP, DIP and AIP, naturally it is impossible to include any of the above types, nearly half of the NSIP specimens Interstitial inflammation is predominant, and the degree of fibrosis is mild or even absent. Chronic inflammatory cells infiltrating the alveolar stroma include: lymphocytes and a large number of plasma cells; the infiltration density of these cells is considered to be the highest among all types of IIP. Therefore, this performance is highly identifiable in histology and is considered to be a specific manifestation of NSIP. In another 40% of cases of NSIP, the degree of infiltration and fibrosis of inflammatory cells is similar; but sometimes, this performance It is also difficult to distinguish from UIP, and the main point of identification is that the overall change of the specimen is quite consistent, there is no obvious honeycomb-like change, fibroblast accumulation area is also rare, and the remaining 10% is mainly composed of interstitial collagen deposition. It can be localized or dispersed; however, active fibroblasts are rarely seen in the sedimentary area, but mostly mature collagen bundles; so it is easy to identify with AIP.

2.ARDS

Its histological features are pulmonary interstitial edema and DAD, and the pathological manifestations of AIP are the proliferation or mechanization of DAD, so both are difficult to identify in clinical manifestations and tissues, but ARDS has multiple primary diseases and clear The cause of the disease, such as infection, trauma, etc., the diagnosis of ARDS should not rely on lung biopsy, combined with clinical trials for typical cases is not difficult, some scholars still speculate that AIP is due to certain viral infections and belongs to the ARDS category, unfortunately There is no evidence, so Ash believes that the identification of the two sometimes requires a lot of work to find the cause of ARDS. From here we can see why some books refer to AIP as idiopathic ARDS and clinically AIP. It is considered to be ARDS. At present, there is a difference between the two. The cause is one aspect. On the other hand, after the application of glucocorticoids, the prognosis of AIP is expected to improve, and the treatment response of ARDs to glucocorticoids is often ineffective. .

3. Occlusive bronchiolitis with organizing pneumonia (BOOP) The incidence is more urgent, but the progress is slow. Multiple plaques on the X-ray chest radiograph often have obvious migration during the course of the disease. The chest CT can be seen as a layer or knot. In the density-increased area of the nodular distribution, no vascular image is seen, and the marginal area has a "gas stagnation". The pathological feature is obstructive bronchiolitis. The granulation tissue is blocked in the enlarged small airway, sometimes extending to the alveolar duct; the alveolar wall and There are mononuclear cell-based infiltrations; these changes are mostly limited to the sub-lobular range, and the lesions and normal areas of the imaging and pathology are clearly defined and usually not confused with AIP. Because DAD has a mechanized period, it is extremely In rare cases, the pathological manifestations of BOOP and NSIP and AIP cannot be distinguished. At this time, the history and clinical manifestations become the main points of differential diagnosis.

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