Shock lung and diffuse alveolar damage pathological and pathogenetic considerations

Diffuse alveolar damage may be caused by any one or more of a large number of injurious agents. While the etiology may be diverse, the pathology is relatively uniform ranging from an acute exudative phase characterized by protein-rich interstitial and alveolar edema, through to a reactive subacute proliferative phase characterized by interstitial fibroplasia and collagenization together with granular pneumocyte hyperplasia. Interstitial inflammation is a variable feature and of course mixed exudative and proliferative features are common. In the clinically overt adult respiratory distress syndrome, the mortality is formidable. The pathogenesis is damage to endothelial cells and membranous pneumocytes. This may be caused by direct chemical action or indirectly through the mediation of oxidizing free radicles or leukotrienes. In diffuse alveolar damage associated with shock, recent work suggests mediation of the cellular injury via complement activation following tissue injury, with the major pathology being due to lysosomal enzyme damage from phagocytes chemotactically attracted to the lung. Etiological factors in diffuse alveolar damage are numerous and details of appropriate primary therapy are therefore diverse. The pathogenesis and pathology are however relatively uniform, calling for uniform supportive therapeutic measures of the clinical adult respiratory distress syndrome.     

Regional alveolar damage (RAD). A localized counterpart of diffuse alveolar damage

Diffuse alveolar damage (DAD) is usually considered a generalized lung process. During five years the authors observed 83 patients with generalized DAD in 827 adult autopsies (10.1%) and 10 patients with identical, but localized, lesions. The authors propose the term regional alveolar damage (RAD) to designate localized "DAD." RAD was unilateral in six patients and most frequently involved the upper lobe. All ten patients had chronic systemic diseases and presented with life-threatening illnesses. The probable causes of RAD were multifactorial and included hypotensive shock, septicemia, pneumonia, hyperoxia, and pancreatitis. All patients developed respiratory failure, requiring supplemental oxygen and, in nine patients, mechanical ventilation. Chest roentgenograms revealed alveolar or combined alveolar and interstitial infiltrates that corresponded to the lesions found at autopsy. The reasons for localization of RAD within the lung are unclear, but the presence of proliferative lesions and frequent involvement of the upper lobe suggests that RAD is not simply an early phase of DAD and implicates additional pathogenetic factors.     

Megakaryocytes and platelet homeostasis in diffuse alveolar damage

Platelet homeostasis reflects a balance between the production of platelets via cytoplasmic fragmentation of megakaryocytes in the pulmonary microvasculature and their catabolism. Increased numbers of megakaryocytes are entrapped in the injured lung, potentially affecting circulating platelet counts. We enumerated pulmonary megakaryocytes and blood platelets in patients with diffuse alveolar damage (DAD) in order to determine their association with clinical outcome. Lung biopsies were examined from 21 patients with histologically documented DAD in its proliferative phase and secondary to a variety of causes. Blood platelet counts were determined within 24 h prior to lung biopsy, and CD61+ pulmonary megakaryocytes were localized in in situ immunohistochemical stains. The overall mortality in this series was 67%. Patients with DAD attributable to drug toxicity (DAD-D) had higher mortality (80%) and greater number of intrapulmonary CD61+ megakaryocytes than those with DAD due to other causes (23+/-7, 10+/-2, p<0.05). Patients with blood platelet counts =350 th/cm(3) showed increased survival (p<0.05). The findings support the hypothesis that abnormal platelet homeostasis is associated with increased mortality in acute lung injury and indicate that thrombocytosis in ARDS is associated with improved survival. The mechanisms of altered platelet homeostasis in DAD merit further investigation.     

Primary choriocarcinoma of the lung manifesting as diffuse alveolar hemorrhage

An autopsy case of primary pulmonary choriocarcinoma that manifested as diffuse alveolar hemorrhage is reported. A 44-year-old nurse presented with fever, dry cough, hemoptysis, and progressive dyspnea, and died after a downhill course of 2 weeks. Chest radiographs showed diffuse parenchymal shadows throughout the entire lung and a nodular lesion in the right lower lobe. Findings suggestive of acute renal failure were not seen. The autopsy revealed primary pure choriocarcinoma of the right lower lobe and diffuse alveolar hemorrhage throughout the entire lung. Findings of small vessel vasculitis ("pulmonary alveolar capillaritis") were not observed, and extensive neoplastic involvement of the pulmonary vasculature was considered the cause of the diffuse alveolar hemorrhage. Small metastatic foci were found in the liver, adrenal glands, pancreas, and ovaries. This case shows that primary pulmonary neoplasms, on rare occasions, can produce the clinical and pathologic features of diffuse alveolar hemorrhage, probably through elevated pulmonary venous pressure caused by extensive destruction of the vasculature.     

The fibrosing process in so-called organized diffuse alveolar damage

Summary On the assumption that some cases of organized diffuse alveolar damage (DAD) result from organization of hyaline membrane, we collected nine autopsy cases of DAD in various stages of the fibrosing process from hyaline membrane to membranous fibrosis and studied changes in the basement membrane and epithelial cells immunohistochemically. In the majority of cases, the following sequence of events was assumed: the hyaline membrane is first formed at the tip of the alveolar septum, a part of the alveolar duct wall where epithelial cells have disappeared. With time it elongates and completely covers alveolar mouths. In the organizing stage, fibroblasts start to permeate through the alveolar duct walls to replace the hyaline membrane completely and to form membranous fibrous tissue. In a few cases, however, fibrous tissue will fill alveolar spaces to form intraluminal diffuse fibrosis. Alveolar epithelial cells and the basement membrane of the alveolar walls are well preserved until the end of the organizing stage when the basement membrane becomes distorted. We believe that membranous fibrosis represents a form of alveolar duct damage and that it differs from diffuse fibrosis, which is indicative of diffuse alveolar damage in the true sense.     

Dimethylthetin treatment causes diffuse alveolar lung damage: a pilot study in a sheep model of Continuous Ambulatory Peritoneal Dialysis (CAPD).

Total plasma homocysteine (Hcy) concentration correlates with risk of vascular disease. Over 80% of chronic renal failure patients have elevated plasma Hcy and a 10-20 times higher incidence of vascular disease. Glycine betaine lowers plasma Hcy through methylation catalysed by betaine-homocysteine methyltransferase (BHMT). Dimethylthetin (DMT), a synthetic glycine betaine analogue, is a more effective BHMT substrate. DMT is therefore a potential therapeutic agent for reducing plasma Hcy in humans and may be particularly useful in renal failure patients receiving dialysis because of chronic betaine depletion as a result of treatment. We aimed to determine whether the addition of DMT to dialysis fluid lowered plasma Hcy concentrations in a Continuous Ambulatory Peritoneal Dialysis sheep model using animals that were either in acute renal failure (n=3) or had normal renal function (n=1). Sub-acute exposure to DMT was toxic to all four animals, which died with total lung consolidation and collapse and Diffuse Alveolar Damage within 48 h of beginning treatment. Adverse side effects were observed after 4-8 doses. DMT was not detected in pre-dialysis plasma samples and the final concentration at death was 0.5-7.8 mmol/L, depending on the number of doses each animal was exposed to. Abnormalities were not observed in animals supplied standard dialysis fluid, or fluid with added glycine betaine. Toxicity associated with DMT treatment raises concerns for its use in further studies. However, sub-acute administration of DMT to sheep may provide a useful model of acute alveolar damage.     

Organizing pneumonia and pulmonary lymphatic architecture in diffuse alveolar damage

Diffuse alveolar damage represents the pathologic basis of most cases of the acute respiratory distress syndrome. Diffuse alveolar damage reflects injury to the pulmonary alveolar wall and microvasculature, leading to the exudation of water and plasma proteins that can overwhelm the local lymphatic drainage. Organizing pneumonia is a prominent histopathologic feature in some cases of diffuse alveolar damage. We examined whether diffuse alveolar damage-organizing pneumonia and changes in lymphatic architecture might be indicators of clinical outcome in acute respiratory distress syndrome. Formalin-fixed lung sections (n = 26) from thoracoscopic lung biopsies of patients with diffuse alveolar damage in the fibroproliferative phase, with or without organizing pneumonia, were immunostained with anti-CD31 and anti-D240, markers of vascular and lymphatic endothelium, respectively, and examined by morphometric analysis. Positively staining vessels were enumerated and maximal luminal diameters recorded in randomly selected low-power fields. Patients with diffuse alveolar damage-organizing pneumonia showed greater survival than those with diffuse alveolar damage (67% versus 33%, P = .03). The maximal luminal diameter of D240+ lymphatic vessels was larger for diffuse alveolar damage-organizing pneumonia than diffuse alveolar damage (28 +/- 4 versus 59 +/- 16 microm, P = .02). In addition, larger lymphatic luminal diameters (28 +/- 4 versus 47 +/- 11 microm) were associated with increased survival (P = .12). We conclude that lung biopsy histopathology and pulmonary lymphatic morphology may predict survival in acute respiratory distress syndrome.     

Acute fibrinous and organizing pneumonia: a histological pattern of lung injury and possible variant of diffuse alveolar damage

CONTEXT: The histologic patterns of diffuse alveolar damage (DAD), bronchiolitis obliterans with organizing pneumonia (BOOP), and eosinophilic pneumonia (EP) are well-recognized histologic patterns of lung injury associated with an acute or subacute clinical presentation. We have recognized acute fibrinous and organizing pneumonia (AFOP) as a histologic pattern, which also occurs in this clinical setting but does not meet the classic histologic criteria for DAD, BOOP, or EP and may represent an underreported variant. OBJECTIVE: To investigate the clinical significance of the AFOP histologic pattern and to explore its possible relationship to other disorders, including DAD and BOOP. DESIGN: Open lung biopsy specimens and autopsy specimens were selected from the consultation files of the Armed Forces Institute of Pathology, which showed a dominant histologic pattern of intra-alveolar fibrin and organizing pneumonia. Varying amounts of organizing pneumonia, type 2 pneumocyte hyperplasia, edema, acute and chronic inflammation, and interstitial widening were seen. Cases with histologic patterns of classic DAD, BOOP, abscess formation, or eosinophilic pneumonia were excluded. To determine the clinical behavior of patients with this histologic finding, clinical and radiographic information and follow-up information were obtained. Statistical analysis was performed using Kaplan-Meier and chi(2) analysis. RESULTS: Seventeen patients (10 men, 7 women) with a mean age of 62 years (range, 33-78 years) had acute-onset symptoms of dyspnea (11), fever (6), cough (3), and hemoptysis (2). Associations believed to be clinically related to the lung disease included definitive or probable collagen vascular disease (3), amiodarone (1), sputum culture positive for Haemophilus influenza (1), lung culture positive for Acinetobacter sp. (1), lymphoma (1), hairspray (1), construction work (1), coal mining (1), and zoological work (1). Six patients had no identifiable origin or association. Follow-up revealed 2 clinical patterns of disease progression: a fulminate illness with rapid progression to death (n = 9; mean survival, 0.1 year) and a more subacute illness, with recovery (n = 8). Histologic analysis and initial symptoms did not correlate with eventual outcome, but 5 of the 5 patients who required mechanical ventilation died (P =.007). CONCLUSIONS: Acute fibrinous and organizing pneumonia is a histologic pattern associated with a clinical picture of acute lung injury that differs from the classic histologic patterns of DAD, BOOP, or EP. Similar to these patterns of acute lung injury, the AFOP pattern can occur in an idiopathic setting or with a spectrum of clinical associations. The overall mortality rate is similar to DAD and therefore may represent a histologic variant; however, AFOP appears to have 2 distinct patterns of disease progression and outcome. The need for mechanical ventilation was the only parameter that correlated with prognosis. None of the patients with a subacute clinical course required mechanical ventilation.     

Chronic progredient diffuse alveolar damage probably related to exposure to herbicides

Summary Clinical history and wedge biopsy specimen findings of a Vietnam veteran suffering from progressive severe tissue damage of lung are presented. The patient served as a soldier in defoliated areas for 2 years and developed severe chest pain and dyspnoea with chronic postnasal dripping, maxillary sinusitis and allergic asthmoid bronchitis with pronounced obstructions and eosinophilia. Recurrent onsets of symptoms over a period of 10 years led to wedge biopsies of the left upper lobe, right lower lobe and mediastinal lymph node. Histology is consistent with chronic, slightly progressive diffuse alveolar damage including moderate interstitial fibrosis. Total destruction of mediastinal lymph node with deposits of amorphous material and foreign body giant cells were noted. Histology findings and clinical course favor hypersensitivity reaction of lung and congestion of exogeneous material probably related to exposure to herbicides.     

Immunohistochemical detection of ubiquitin-positive intracytoplasmic eosinophilic inclusion bodies in diffuse alveolar damage

AIMS: To clarify the relationship between ubiquitin-positive pneumocytes and intracytoplasmic eosinophilic inclusion bodies (IB) in patients who died of diffuse alveolar damage (DAD). METHODS AND RESULTS: Eighteen patients with DAD were studied, in whom hyaline membranes were present in one or more out of five sections from each lobe of the lungs and 15 patients with no DAD. Light microscopy revealed hyaline membrane in over 25% of lobes from 18 patients with DAD. The cytoplasm of pneumocytes from six of 18 cases of DAD contained IB. Immunohistochemically, all IBs were characteristically positive for both ubiquitin (Ub) and cytokeratin KL-1. Cytoplasmic granules were also Ub+ in four cases of DAD without IB. IB+ or Ub+ pneumocytes were undetectable in non-DAD patients. We evaluated DAD severity based on hyaline membrane formation; the mean score in DAD with IB (3.60; n = 6) was significantly higher than that in Ub- (2.92; n = 8). Ub+ pneumocytes were found with or without IB among those cases with high DAD scores. CONCLUSIONS: These findings suggest that disordered proteolysis in the Ub-mediated proteasome system leads to the accumulation of abnormal ubiquitinated protein, which includes cytokeratin, in pneumocytes. This is the first report to suggest that Ub+ pneumocytes are associated with disease severity in patients with DAD.     

A new model of diffuse interstitial pulmonary fibrosis in the rat

We have produced experimental diffuse interstitial pulmonary fibrosis in rats with a combination of low and repeated doses of paraquat plus continuous exposure to normobaric 74% O2 in the breathing air for several weeks. Pulmonary fibrosis was evaluated histologically and biochemically, through the determination of total collagen content in the lung. Our procedure is characterized by low initial mortality, the development of extensive distortion of the pulmonary architecture, and the presence of severe and diffuse interstitial fibrosis. The model was compared with bleomycin-induced pulmonary fibrosis in the same rat strain, in which the process is focal and leaves most of the lung unaffected. We conclude that lung damage produced by the combination of low doses of paraquat plus normobaric 74% O2 concentration in the breathing air is an adequate experimental model of diffuse interstitial pulmonary fibrosis as it occurs in many of the human cases of this condition.     

A nude mouse model of human osteosarcoma lung metastases for evaluating new therapeutic strategies

The purpose of these studies was to develop a metastatic osteosarcoma nude mouse model to evaluate the in vivo efficacy of new therapeutic compounds. Human SAOS-2 osteosarcoma cells (10⁶ cells) were injected i.v. into nude mice. Cells isolated from a rare pulmonary metastases 6 months later were established (SAOS-LM1) in culture and re-injected. This procedure was repeated 5 additional times to produce the SAOS-LM6 cell line. Visible pulmonary nodules were present 8 weeks following i.v. injection of 10⁶ SAOS-LM6 cells as compared to 17 weeks using SAOS-LM2 cells. Microscopic SAOS-LM6 pulmonary metastases were demonstrated at 6 weeks. Administration of adriamycin on week 9 resulted in regression of macroscopic SAOS-LM6 lung tumors. The ability of the model to be used to evaluate the effectiveness of a biologic agent against microscopic disease was also verified. It was concluded that this model can assess therapeutic efficacy and therefore, may have a role in investigating the potential of novel approaches aimed at eliminating pulmonary metastatic osteosarcoma. This revised version was published online in July 2006 with corrections to the Cover Date.     

Respiratory reovirus 1/L induction of diffuse alveolar damage: a model of acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is a clinical syndrome that is characterized by diffuse alveolar damage usually secondary to an intense host inflammatory response of the lung to a pulmonary or extrapulmonary infectious or noninfectious insult. In this report we describe a unique animal model in which CBA/J mice infected with reovirus serotype 1, strain Lang develop ARDS. This model recapitulates the histopathological changes observed in human ARDS, which consists of the overlapping phases of exudation including the formation of hyaline membranes, regeneration, and healing via resolution and/or repair with fibrosis. While the consequences of a number of infectious and noninfectious insults in various animal systems have been developed as models of human ARDS, they are models of acute lung injury and are of short-term duration. Therefore, they do not recapitulate all of the clinical and pathological phases observed in human ARDS. Thus, study of the cellular and molecular factors involved in these distinct phases of the disease have been limited. Reovirus 1/L infection of CBA/J mice will allow investigations of the pathophysiology of ARDS as it progresses from the initial stages of edema and neutrophilia to fibrotic lesion development in late stages.     

Rare diffuse diseases of the lung. Pulmonary alveolar proteinosis, lymphangioleiomyomatosis, amyloidosis

Pulmonary alveolar proteinosis (PAP), lymphangioleyomiomatosis (LAM) and amyloidosis are three unrelated diseases of rare occurrence, with characteristic histopathological features. A pattern of alveolar filling with granular pink material accumulation is characteristic of PAP. This material can be recognized in lung biopsies, but also in bronchial lavage fluid. PAP is clinically related to the abnormal clearance of alveolar surfactant, most commonly due to the disruption of the granulocyte macrophage-colony stimulating factor signalling pathway. Whole lung lavage is the treatment of choice. LAM is characterized by cystic lung degeneration and interstitial proliferation of LAM cells, which express both melanocyte and smooth muscle cell markers, has a typical cystic pattern on CT scan, can be associated clinically with abdominal angiomyolipomas and limphangioleiomyomas, and occurs in female patients, either in isolation or as a manifestation of tuberous sclerosis. Sex hormone manipulation is the therapy of choice in this otherwise progressive disease. Diffuse interstitial or perivascular amyloid deposits in the lung can form in the context of systemic amyloidosis, usually associated with myeloma or monoclonal gammopathy, and less often with chronic inflammatory diseases. Nodular amyloid deposits, in contrast, are not associated with systemic lung disease, and present instrumentally as a coin lesion or lung mass. Isolated tracheobronchial amyloidosis is another rare form that is not related to systemic disease. In all conditions, amyloid has a typical waxy, amorphous, slightly eosinophilic stain, stains red with Congo red and presents a characteristic apple-green birefringence under polarized light, which is essential for diagnosis.     

Alveolar basement membrane breaks down in diffuse alveolar damage: An immunohistochemical study

Sequential structural changes of the alveoli in diffuse alveolar damage (DAD) were examined by immunohistochemical methods. Lung specimens obtained at autopsy from 52 patients with DAD were stained with antibodies to laminin, 7S collagen (7S) and type IV collagen (type IV) for alveolar basement membrane, to von Willebrand factor, CD-31 and thrombomodulin (TM) for the alveolar capillary endothelial cell, and to epithelial membrane antigen and surfactant apo-protein (PE-10) for the alveolar epithelium. Forty-two of the patients had the exudative form of DAD; 10 of the patients had the proliferative form of DAD. The results were summarized as follows: (i) laminin was most easily impaired both in the epithelial and capillary basement membrane in the early exudative stage; (ii) following laminin, 7S and type IV in the capillary basement membrane were also injured in the early exudative stage, and recovered in the proliferative stage; (iii) subsequently, 7S and type IV in the epithelial basement membrane were also impaired in the late exudative stage, and remained impaired even in the proliferative stage; and (iv) alveolar epithelium regenerated almost completely in the late exudative stage, but staining for TM in the alveolar capillary recovered in the proliferative stage. Because the alveolar basement membrane must govern the homeostasig of alveolar tissue architecture, it was concluded that its preservation is necessary to avoid the abnormal remodeling of the alveoli in the reparative stage of DAD, if the patient survives the acute episodes of the disease.     

Terminal diffuse alveolar damage in relation to interstitial pneumonias. An autopsy study

Acute exacerbations of idiopathic pulmonary fibrosis/cryptogenic fibrosing alveolitis (IPF/CFA) are rare and typically terminal events, but their relationship to underlying patterns of idiopathic interstitial pneumonias is unknown. We reviewed autopsy material from patients who died of diffuse alveolar damage in the clinical setting of pulmonary fibrosis, both idiopathic and with background fibrosing alveolitis with connective tissue disorders (FA-CTDs), and compared them with cases of acute interstitial pneumonia. Of 15 patients with acute exacerbations of IPF/CFA (n = 12) or FA-CTD (n = 3), 12 had a background pattern of usual interstitial pneumonia and 3 had fibrotic nonspecific interstitial pneumonia. All cases of fibrotic nonspecific interstitial pneumonia were seen in association with FA-CTD. The cause of acute exacerbations is unknown, but our data suggest that toxic effects of oxygen and triggering infection are unlikely causes. In patients with CTDs, it remains uncertain whether the acute exacerbation is related to the fibrosis, the associated CTD, or a combination of these factors. Acute exacerbations of IPF/CFA may be a more common terminal event than previously thought.     

A new murine model of aging lung: the senescence accelerated mouse (SAM)-P.

The senescence accelerated mouse (SAM) has recently been characterized as a unique model to investigate age-related disorders, including amyloidosis, cataract, osteoporosis and dementia. However, little is known as to the properties of the lung in these animals. Tobacco smoke is also associated with enhanced loss of elastic recoil and the development of emphysema. We have attempted to examine morphological as well as biochemical changes of the distal lung in SAM-P/2, as the senescence-prone series and SAM-R/1, as the senescence-resistant series. The animals were intermittently exposed to tobacco smoke or air by Hamburg II machines for 5 weeks. Then both groups of animals were killed for histologic and biochemical study. Compared with SAM-R/1, SAM-P/2, even with air exposure, showed a higher value of the mean linear intercept without alveolar wall destruction. It became even greater due to tobacco exposure with emphysematous change. Tobacco exposure accumulated inflammatory cells into alveoli in SAM-P/2, but not in SAM-R/1. Oxygen radical generation by those cells was also higher in SAM-P/2. Analysis of bronchoalveolar lavage fluid in SAM-P/2 after tobacco exposure disclosed increases in albumin content, total protein content and elastase-like activity. There were decreases in the ratio of elastase inhibitory capacity (EIC) to trypsin inhibitory capacity (TIC), contents of glutathione and total free thiol groups. Moreover, SAM-P/2 showed significantly lower EIC/TIC ratio in serum, even with air exposure, than that of SAM-R/1. These results indicate that SAM-P/2 can be a good model for the study of natural evolution of the aging lung as well as its susceptibility to tobacco smoke in the development of emphysema.