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Alveolarproteinose
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Pulmonary alveolar proteinosis (PAP) is a rare respiratory syndrome characterised by the accumulation of surfactant lipoproteins within the alveoli. According to various pathogenetic mechanisms and aetiologies, PAP is classified as primary, secondary or congenital. Primary PAP is led by a granulocyte–macrophage colony-stimulating factor (GM-CSF) signalling disruption; the autoimmune form is driven by the presence of anti GM-CSF autoantibodies and represents 90% of all the PAP cases; and the hereditary form is the result of mutations in genes encoding GM-CSF receptor. Secondary PAP is associated with various diseases causing a reduction in function and/or number of alveolar macrophages. Congenital PAP emerges as a consequence of corrupted surfactant production, due to mutations in surfactant proteins or lipid transporter, or mutations affecting lung development. The clinical manifestations are various, ranging from insidious onset to acute or progressive respiratory failure, including premature death within the first days of life in neonates with congenital surfactant production disorders. The diagnostic workup includes clinical and radiological assessment (respiratory function test, high-resolution chest computed tomography), laboratory tests (anti-GM-CSF autoantibodies dosage, GM-CSF serum level and GM-CSF signalling test), and genetic tests. Whole-lung lavage is the current gold standard of care of PAP; however, the therapeutic approach depends on the pathogenic form and disease severity, including GM-CSF augmentation strategies in autoimmune PAP and other promising new treatments.
Educational aims
To update knowledge about a rare respiratory syndrome, pulmonary alveolar proteinosis, in order to promote early diagnosis and correct management.
To highlight recent treatment options based on pathogenesis and disease severity.
Background:
Secondary pulmonary alveolar proteinosis (sPAP) is an extremely rare disease. The clinical features of sPAP patients remain to be summarizeds.
Methods:
Patients pathologically diagnosed with PAP and with negative results for anti-granulocyte macrophage colony stimulating factor (GM-CSF) autoantibodies from Peking Union Medical College Hospital between January 2000 and July 2016 were retrospectively studied. The PubMed database was also searched for literature to collect published cases.
Results:
In our center, nine patients were diagnosed as sPAP with a median age of 37 years. Hematological disorders, including myelodysplastic syndrome (MDS), chronic myelogenous leukemia (CML), and pulmonary tuberculosis (TB) infection were the underlying diseases. Cases secondary to MDS had very poor prognosis as all of them survived less than 2 years after their diagnosis, while those secondary to TB had favorable prognosis. Only 33.3% of cases showed interlobular septal thickening in our sPAP group. Through literature review, 164 sPAP cases were collected. The age at diagnosis was 45.0 ± 14.8 years old and the gender radio was 1.20:1 (M:F). 61.9% of cases were diagnosed by bronchoscopy. MDS and CML were common underlying diseases in 34.1% and 15.2% of patients, respectively. Patients with sPAP secondary to hematological diseases had a short survival time and half of them died within 14.95 months after diagnosis.
Conclusions:
MDS and TB infection were the most frequent underlying causes of sPAP in this single-center research in China, with cases secondary to MDS having a poor survival rate. sPAP was more likely to be secondary to hematological disorders, especially MDS and CML and had a fairly poor prognosis in published cases. sPAP should be suspected in PAP patients whose CT scan presents only ground-glass opacities without interlobular septal thickening.
Autoimmune pulmonary alveolar proteinosis is a rare disease characterized by myeloid cell dysfunction, abnormal pulmonary surfactant accumulation, and innate immune deficiency. It has a prevalence of 7-10 per million, occurs in individuals of all races, geographic regions, gender, and socioeconomic status, and accounts for 90% of all patients with PAP syndrome. The most common presentation is dyspnea of insidious onset with or without cough, production of scant white-frothy sputum, and diffuse radiographic infiltrates in a previously healthy adult - but can also occur in children as young as 3-years. Digital clubbing, fever, and hemoptysis are not typical and the latter two indicate intercurrent infection may be present. Low prevalence and nonspecific clinical, radiological and laboratory findings commonly lead to misdiagnosis as pneumonia and substantially delay an accurate diagnosis. The clinical course, while variable, usually includes progressive hypoxemic respiratory insufficiency and, in some patients, secondary infections, pulmonary fibrosis, respiratory failure, and death. Two decades of research have raised autoimmune PAP from obscurity to a paradigm of molecular pathogenesis-based diagnostic and therapeutic development. Pathogenesis is driven by GM-CSF autoantibodies, which are present at high levels in blood and tissues and form the basis of an accurate, commercially available diagnostic blood test with a sensitivity and specificity of 100%. Although whole lung lavage remains first-line therapy, inhaled GM-CSF is a promising pharmacotherapeutic approach demonstrated in well-controlled trials to be safe, well-tolerated, and efficacious. Research has established GM-CSF as a pulmonary regulatory molecule critical to surfactant homeostasis, alveolar stability, lung function, and host defense.
PAP is an ultra‐rare disease in which surfactant components, that impair gas exchange, accumulate in the alveolae. There are three types of PAP. The most frequent form, primary PAP, includes autoimmune PAP which accounts for over 90% of all PAP, defined by the presence of circulating anti‐GM‐CSF antibodies. Secondary PAP is mainly due to haematological disease, infections or inhaling toxic substances, while genetic PAP affects almost exclusively children. PAP is suspected if investigation for ILD reveals a crazy‐paving pattern on chest CT scan, and is confirmed by a milky looking BAL that gives a positive PAS reaction indicating extracellular proteinaceous material. PAP is now rarely confirmed by surgical lung biopsy. WLL is still the first‐line treatment, with an inhaled GM‐CSF as second‐line treatment. Inhalation has been found to be better than subcutaneous injections. Other treatments, such as rituximab or plasmapheresis, seem to be less efficient or ineffective. The main complications of PAP are due to infections by standard pathogens (Streptococcus, Haemophilus and Enterobacteria) or opportunistic pathogens such as mycobacteria, Nocardia, Actinomyces, Aspergillus or Cryptococcus. The clinical course of PAP is unpredictable and spontaneous improvement can occur. The 5‐year actuarial survival rate is 95%.
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Pulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by the accumulation of surfactant in alveoli and terminal airways resulting in respiratory failure. PAP comprises part of a spectrum of disorders of surfactant homeostasis (clearance and production). The surfactant production disorders are caused by mutations in genes required for normal surfactant production. The PAP syndrome is identified based on history, radiologic, and bronchoalveolar lavage and/or histopathologic findings. The diagnosis of PAP-causing diseases in secondary PAP requires further studies. Whole-lung lavage is the current standard therapy and promising new pharmacologic therapies are in development.
