Pulmonary alveolar proteinosis (PAP) is characterized by massive accumulation of surfactants in the alveolar cavities, mainly caused by anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies in the body leading to the clearance dysfunction of surfactants by alveolar macrophages.
Etiology
It is currently believed that the etiology of this disease may include hypertrophy and hyperplasia of alveolar type II epithelial cells, uncleaned excessive secretion of lamellar bodies in the alveolar cavities; increased surfactants stimulating hyperplasia of macrophages, phagocytosis of pulmonary surfactants by macrophages, macrophage lysis releasing cell contents into the alveolar cavity: GM-CSF deficiency; and inhalation of harmful substances, such as insulating fiber materials, silicon, and aluminum.
Clinical manifestations
Most patients have progressively exacerbated dyspnea on exertion and cough，mainly dry cough. Cough and expectoration are common in smokers. The characteristics of sputum are generally not helpful for diagnosis. Hemoptysis and thoracodynia may occur. Fever is less common, but may occur in secondary infection. Physical examination results are nonspecific, but 50% of patients may have inspiratory crackles or velcro crackles, 25% of patients have cyanosis, and about 20% of patients have clubbed fingers.
Auxiliary examination
Chest x-ray shows bilateral diffuse alveolar exudation around the hilum of the lung, forming a butterfly pattern. Generally, extensive pulmonary exudation is inconsistent with mild clinical symptoms. The characteristic manifestations of chest HRCT are ground-glass opacity sharply marginated from normal lung tissue, forming geographic pattern; and thickened interlobular septa and intralobular septa, forming polygonal or crazy paving pattern.
Diagnosis
The characteristic physiological function change is severe hypoxemia caused by intrapulmonary shunt. The bronchoalveolar lavage fluid (BALF) is characteristically milky white, thick, and opaque; and precipitates and stratifies after standing. Positive periodic acid Schiff (PAS) staining of cells in BALF or tissue in transbronchial lung biopsy (TBLB) and negative alcian blue staining can confirm the diagnosis.
Treatment
1/3 of patients can relieve spontaneously. In patients with obvious respiratory dysfunction, whole lung lavage is preferred.
Recently, it has been found that some patients respond well to GM-CSF replacement therapy.