Pulmonary alveolar proteinosis | |
---|---|
Other names | alveolar proteinosis |
Micrograph of pulmonary alveolar proteinosis, showing the characteristic airspace filling with focally dense globs referred to as chatter or dense bodies. H&E stain. | |
Specialty | Pulmonology |
Pulmonary alveolar proteinosis (PAP) is a rare lung disorder characterized by an abnormal accumulation of surfactant-derived lipoprotein compounds within the alveoli of the lung. The accumulated substances interfere with the normal gas exchange and expansion of the lungs, ultimately leading to difficulty breathing and a predisposition to developing lung infections. The causes of PAP may be grouped into primary (autoimmune PAP, hereditary PAP), secondary (multiple diseases), and congenital (multiple diseases, usually genetic) causes, although the most common cause is a primary autoimmune condition in an individual.
The signs and symptoms of PAP include shortness of breath, [1] cough, low grade fever, and weight loss. Additionally, the clinical course of PAP is unpredictable. Spontaneous remission is recognized, and some patients have stable symptoms. Death may occur due to the progression of PAP or of any underlying associated disease. Individuals with PAP are more vulnerable to lung infections such as nocardiosis, Mycobacterium avium-intracellulare infection, or fungal infections. [1]
The abnormal accumulation of lipoproteinaceous compounds in PAP is due to impaired surfactant regulation and clearance. This is usually related to impaired alveolar macrophage function. [2] In adults, the most common cause of PAP is an autoimmunity to granulocyte-macrophage colony stimulating factor (GM-CSF), a critical factor in development of alveolar macrophages. Decreased bioavailability of GM-CSF results in poor alveolar macrophages development and function, which results in accumulation of surfactant and related products. [2]
Secondary causes of PAP are those in which the accumulation of lipoproteinaceous compounds is secondary to another disease process. This has been recognized in the settings of certain cancers (such as myeloid leukemia), lung infections, or environmental exposure to dusts or chemicals, such as nickel. [3]
Although the cause of PAP was not originally understood, a major breakthrough in the understanding of the cause of the disease came by the chance observation that mice bred for experimental study to lack a hematologic growth factor known as granulocyte-macrophage colony stimulating factor (GM-CSF) developed a pulmonary syndrome of abnormal surfactant accumulation resembling human PAP. [4]
The implications of this finding are still being explored, but significant progress was reported in February 2007. Researchers in that report discussed the presence of anti-GM-CSF autoantibodies in patients with PAP, and duplicated that syndrome with the infusion of these autoantibodies into mice. [5]
Familial or sporadic inactivating mutations in one of the two parental GATA2 genes produces an autosomal dominant disorder termed GATA2 deficiency. The GATA2 gene produces the GATA2 transcription factor which is critical for the embryonic development, maintenance, and functionality of blood-forming, lympathic-forming, and other tissue-forming cells. Individuals with a single GATA2 inactivating mutation present with a wide range of disorders including pulmonary alveolar proteinosis. GATA2 mutation-based pulmonary alveolar proteinosis is associated with normal levels of GM-CSF and commonly improves or is avoided in afflicted individuals who successfully receive a hematopoietic stem cell transplantation. [6] [7]
Hereditary pulmonary alveolar proteinosis is a recessive genetic condition in which individuals are born with genetic mutations that deteriorate the function of the CSF2 receptor alpha on alveolar macrophages. Consequently, a messenger molecule known as granulocyte/macrophage-colony stimulating factor (GM-CSF) is unable to stimulate alveolar macrophages to clear surfactant, leading to difficulty with breathing. The gene for the CSF2 receptor alpha is located in the 5q31 region of chromosome 5, and the gene product can also be referred to as granulocyte macrophage colony-stimulating factor receptor. [8] [9]
The diagnosis of PAP is made using a combination of a person's symptoms, chest imaging, and microscopic evaluation of lung washing/tissue. Additional testing for serum anti-GM-CSF antibodies are helpful for confirmation. [10]
Although both the symptoms and imaging findings are stereotypical and well-described, they are non-specific and indistinguishable from many other conditions. For example, chest x-ray may show alveolar opacities, and a CT may show a crazy paving lung pattern, both of which are seen more commonly in numerous other conditions. [11] Thus, the diagnosis primarily depends on the pathology findings.[ citation needed ]
Lung washings or tissue for histopathologic analysis are most commonly obtained using bronchoalveolar lavage and/or lung biopsy. [12] Characteristic biopsy findings show filling of the alveoli (and sometimes terminal bronchioles) with an amorphous eosinophilic material, which stains strongly positive on PAS stain and the PAS diastase stain. The surrounding alveoli and pulmonary interstitium remain relatively normal. [13] Electron microscopy of the sample, although not typically performed due to impracticality, shows lamellated bodies representing surfactant. [14] An alternative diagnosis with similar histomorphologic findings is Pneumocystis jirovicii pneumonia. [14]
Lung washings characteristically yield a fluid which is "milky"composition. Under the microscope, samples show 20-50 micrometer PAS-positive globules on a background of finely granular or amorphous PAS-positive material. There is typically a low numbers of macrophages and inflammatory cells (although this is variable). [13] [14]
The standard treatment for PAP is whole-lung lavage [15] [16] [17] and supportive care. [18] [19] [20] Whole lung lavage is a procedure performed under general anesthesia, in which one lung is pumped with oxygen (ventilated lung), and the other lung (non-ventilated lung) is filled with a warm saline solution (up to 20 L) and drained, removing any proteinaceous effluent along with it. [21] This is generally effective at improving PAP symptoms, often for a prolonged period of time. Other treatments still being studied include subcutaneous and inhaled GM-CSF, and rituximab, an intravenous infusion that works to stop the production of the autoantibodies responsible for autoimmune PAP. [18] [19] [20] [22] Lung transplantation has been performed in individuals with the various forms of PAP; however, this is often only used when all other treatment options have failed and significant lung damage has developed due to the risks, complications, or recurrence of PAP following transplantation. [20] [22] [23] As of 2022, methionine oral supplementation has been tested on patients with methionine tRNA synthetase-related PAP and has strong evidence of its efficacy on these patients. [24]
The disease is more common in males and in tobacco smokers.[ citation needed ]
In a recent epidemiologic study from Japan, [25] Autoimmune PAP has an incidence and prevalence higher than previously reported and is not strongly linked to smoking, occupational exposure, or other illnesses. Endogenous lipoid pneumonia and non-specific interstitial pneumonitis has been seen prior to the development of PAP in a child. [26]
PAP was first described in 1958 [27] by the physicians Samuel Rosen, Benjamin Castleman, and Averill Liebow. [28] In their case series published in the New England Journal of Medicine on June 7 of that year, they described 27 patients with pathologic evidence of periodic acid Schiff positive material filling the alveoli. This lipid rich material was subsequently recognized to be surfactant.[ citation needed ]
The reported treatment of PAP using therapeutic bronchoalveolar lavage was in 1960 by Dr. Jose Ramirez-Rivera at the Veterans' Administration Hospital in Baltimore, [29] who described repeated "segmental flooding" as a means of physically removing the accumulated alveolar material. [30]
PAP is one of the rare lung diseases currently being studied by the Rare Lung Diseases Consortium. The consortium is part of the Rare Diseases Clinical Research Network, an initiative of the Office of Rare Diseases Research, of the National Center for Advancing Translational Sciences, and dedicated to developing new diagnostics and therapeutics for patients with rare lung diseases, through collaboration between the National Institutes of Health, patient organizations and clinical investigators.[ citation needed ]
A pulmonary alveolus, also known as an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where pulmonary gas exchange takes place. Oxygen is exchanged for carbon dioxide at the blood–air barrier between the alveolar air and the pulmonary capillary. Alveoli make up the functional tissue of the mammalian lungs known as the lung parenchyma, which takes up 90 percent of the total lung volume.
Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of respiratory diseases affecting the interstitium and space around the alveoli of the lungs. It concerns alveolar epithelium, pulmonary capillary endothelium, basement membrane, and perivascular and perilymphatic tissues. It may occur when an injury to the lungs triggers an abnormal healing response. Ordinarily, the body generates just the right amount of tissue to repair damage, but in interstitial lung disease, the repair process is disrupted, and the tissue around the air sacs (alveoli) becomes scarred and thickened. This makes it more difficult for oxygen to pass into the bloodstream. The disease presents itself with the following symptoms: shortness of breath, nonproductive coughing, fatigue, and weight loss, which tend to develop slowly, over several months. The average rate of survival for someone with this disease is between three and five years. The term ILD is used to distinguish these diseases from obstructive airways diseases.
Granulocyte-macrophage colony-stimulating factor (GM-CSF), also known as colony-stimulating factor 2 (CSF2), is a monomeric glycoprotein secreted by macrophages, T cells, mast cells, natural killer cells, endothelial cells and fibroblasts that functions as a cytokine. The pharmaceutical analogs of naturally occurring GM-CSF are called sargramostim and molgramostim.
Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water interface of alveoli, with hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
Pulmonary hemorrhage is an acute bleeding from the lung, from the upper respiratory tract and the trachea, and the pulmonary alveoli. When evident clinically, the condition is usually massive. The onset of pulmonary hemorrhage is characterized by a cough productive of blood (hemoptysis) and worsening of oxygenation leading to cyanosis. Treatment should be immediate and should include tracheal suction, oxygen, positive pressure ventilation, and correction of underlying abnormalities such as disorders of coagulation. A blood transfusion may be necessary.
Pneumonitis describes general inflammation of lung tissue. Possible causative agents include radiation therapy of the chest, exposure to medications used during chemo-therapy, the inhalation of debris, aspiration, herbicides or fluorocarbons and some systemic diseases. If unresolved, continued inflammation can result in irreparable damage such as pulmonary fibrosis.
Cryptogenic organizing pneumonia (COP), formerly known as bronchiolitis obliterans organizing pneumonia (BOOP), is an inflammation of the bronchioles (bronchiolitis) and surrounding tissue in the lungs. It is a form of idiopathic interstitial pneumonia.
Bronchoalveolar lavage (BAL), also known as bronchoalveolar washing, is a diagnostic method of the lower respiratory system in which a bronchoscope is passed through the mouth or nose into an appropriate airway in the lungs, with a measured amount of fluid introduced and then collected for examination. This method is typically performed to diagnose pathogenic infections of the lower respiratory airways, though it also has been shown to have utility in diagnosing interstitial lung disease. Bronchoalveolar lavage can be a more sensitive method of detection than nasal swabs in respiratory molecular diagnostics, as has been the case with SARS-CoV-2 where bronchoalveolar lavage samples detect copies of viral RNA after negative nasal swab testing.
Lipoid pneumonia is a specific form of lung inflammation (pneumonia) that develops when lipids enter the bronchial tree. The disorder is sometimes called cholesterol pneumonia in cases where that lipid is a factor.
Alveolar lung diseases, are a group of diseases that mainly affect the alveoli of the lungs.
The granulocyte-macrophage colony-stimulating factor receptor, also known as CD116, is a receptor for granulocyte-macrophage colony-stimulating factor, which stimulates the production of white blood cells. In contrast to M-CSF and G-CSF which are lineage specific, GM-CSF and its receptor play a role in earlier stages of development. The receptor is primarily located on neutrophils, eosinophils and monocytes/macrophages, it is also on CD34+ progenitor cells (myeloblasts) and precursors for erythroid and megakaryocytic lineages, but only in the beginning of their development.
Desquamative interstitial pneumonia (DIP) is a form of idiopathic interstitial pneumonia featuring elevated numbers of macrophages within the alveoli of the lung. The alveolar macrophages have a characteristic light brown pigmentation and accumulate in the alveolar lumen and septa regions of the lower lobes of the lungs. The typical effects of the macrophage accumulation are inflammation and later fibrosis of the lung tissue.
MonoMAC syndrome is a rare autosomal dominant syndrome associated with: monocytopenia, B and NK cell lymphopenia; mycobacterial, viral, fungal, and bacterial opportunistic infections; and virus infection-induced cancers. The disorder often progresses to the development of myelodysplasia, myeloid leukemias, and other types of cancer. MonoMAC is a life-threatening and precancerous disorder.
Tolerogenic therapy aims to induce immune tolerance where there is pathological or undesirable activation of the normal immune response. This can occur, for example, when an allogeneic transplantation patient develops an immune reaction to donor antigens, or when the body responds inappropriately to self antigens implicated in autoimmune diseases. It must provide absence of specific antibodies for exactly that antigenes.
Indium lung is a rare occupational lung disease caused by exposure to respirable indium in the form of indium tin oxide. It is classified as an interstitial lung disease.
Pulmonary alveolar microlithiasis (PAM) is a rare, inherited disorder of lung phosphate balance that is associated with small stone formation in the airspaces of the lung. Mutations in the gene SLC34A2 result in loss of a key sodium, phosphate co-transporter, known to be expressed in distal alveolar type II cells, as well as in the mammary gland, and to a lesser extent in intestine, kidney, skin, prostate and testes. As the disease progresses, the lung fields become progressively more dense (white) on the chest xray, and low oxygen level, lung inflammation and fibrosis, elevated pressures in the lung blood vessels, and respiratory failure ensue, usually in middle age. The clinical course of PAM can be highly variable, with some patients remaining asymptomatic for decades, and others progressing more rapidly. There is no effective treatment, and the mechanisms of stone formation, inflammation and scarring are not known.
GATA2 deficiency is a grouping of several disorders caused by common defect, namely, familial or sporadic inactivating mutations in one of the two parental GATA2 genes. Being the gene haploinsufficient, mutations that cause a reduction in the cellular levels of the gene's product, GATA2, are autosomal dominant. The GATA2 protein is a transcription factor critical for the embryonic development, maintenance, and functionality of blood-forming, lymphatic-forming, and other tissue-forming stem cells. In consequence of these mutations, cellular levels of GATA2 are deficient and individuals develop over time hematological, immunological, lymphatic, or other presentations that may begin as apparently benign abnormalities but commonly progress to severe organ failure, opportunistic infections, virus infection-induced cancers, the myelodysplastic syndrome, and/or leukemia. GATA2 deficiency is a life-threatening and precancerous condition.
Otilimab is a fully human antibody which has been developed by the biotechnology company MorphoSys. It can also be referred to as HuCAL antibody, HuCAL standing for Human Combinatorial Antibody Library and being a technology used to generate monoclonal antibodies. Otilimab is directed against the granulocyte-macrophage colony stimulating factor (GM-CSF), a monomeric glycoprotein functioning as a cytokine promoting both proliferation and activation of macrophages and neutrophils.
Lipid-laden alveolar macrophages, also known as pulmonary foam cells, are cells found in bronchoalveolar lavage (BAL) specimens that consist of macrophages containing deposits of lipids (fats). The lipid content of the macrophages can be demonstrated using a lipid targeting stain like Oil Red O or Nile red. Increased levels of lipid-laden alveolar macrophages are associated with various respiratory conditions, including chronic smoking, gastroesophageal reflux, lipoid pneumonia, fat embolism, pulmonary alveolar proteinosis and pulmonary aspiration. Lipid-laden alveolar macrophages have been reported in cases of vaping-associated pulmonary injury.
Whole lung lavage (WLL), also called lung washing, is a medical procedure in which the patient's lungs are washed with saline by filling and draining repeatedly. It is used to treat pulmonary alveolar proteinosis, in which excess lung surfactant proteins prevent the patient from breathing. Some sources consider it a variation of bronchoalveolar lavage.