Correct!
5. All of
the above
While whole-lung lavage is the most widely utilized and effective therapy for patients with pulmonary alveolar proteinosis, all of the listed therapies have been used to successfully treat patients with this condition.
Discussion:
Pulmonary alveolar
proteinosis (PAP) is a rare group of disorders characterized by deposition of
surfactant-like material in the alveoli. PAP belongs to a heterogeneous group
of disorders defined as alveolar filling syndromes (1).
Alveolar hemorrhage, pulmonary edema, diffuse alveolar damage, eosinophilic
pneumonia and Pneumocystis jiroveci pneumonia are some of the more
common causes of alveolar filling syndromes (2)
. Knowledge of various alveolar filling processes which can present with a
radiological pattern similar to PAP is useful to avoid diagnostic errors.
PAP was first described in a series of 27 patients in 1958 as a “remarkable disease of the lung that consists of the filling of the alveoli by a PAS-positive proteinaceous material, rich in lipid” (3). Since then, PAP has been reported in the medical literature under various terms: alveolar proteinosis, alveolar lipoproteinosis, alveolar phospholipidosis, pulmonary alveolar lipoproteinosis and pulmonary alveolar phospholipoproteinosis.
PAP is now considered to be a group of disorders, each with a distinct etiology and pathogenesis. Primary PAP is caused by disruption of granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling (4) . Primary PAP is further divided into autoimmune and hereditary forms. Autoimmune PAP is characterized by loss of GM-CSF signaling due to the presence of neutralizing GM-CSF antibodies (4,5) . Hereditary PAP is caused by gene mutations involving loss of GM-CSF signaling (4) . This classification has important implications for treatment of PAP, as exogenous GM-CSF is only likely to be useful in treating the GM-CSF antibody positive form of PAP. Various agents have been implicated in pathogenesis of secondary PAP, including dusts, fumes, chronic infections, hematological disorders, and immunodeficiency states. The pathogenesis of secondary PAP is poorly understood. Inhaled silica in animal models has been shown to result in PAP, but this mechanism is poorly understood (6) . The autoimmune form accounts for 90% of primary PAP cases, and hematological disorders constitute 90% of all causes of secondary PAP (7) .
The majority of patients with PAP suffer from gradually worsening dyspnea on exertion and cough. Physical examination is usually unremarkable (8) . A disease severity score for PAP has been proposed based on presence of symptoms and degree of hypoxia; however, the utility of this sore requires further investigation (8) .
The diagnosis of PAP can be established by bronchoalveolar lavage in nearly 70% of patients, although some patients may require transbronchial or surgical lung biopsies (8) . Bronchoalveolar lavage in PAP has a characteristic milky appearance which, on light microscopy, shows acellular globules that are basophilic on Giemsa staining and positive with PAS staining. Although, electron microscopy is usually not required to establish the diagnosis of PAP, it typically shows characteristic myelin-like multi-lamellated structures, debris and foamy macrophages.
Chest radiography in patients with PAP usually shows diffuse, bilateral symmetric, linear and reticular abnormalities superimposed on areas of hazy ground-glass attenuation, but these findings are not pathognomonic of PAP. HRCT typically shows multifocal, bilateral areas of geographically distributed ground-glass opacity that often has a sharp demarcation between normal and abnormal lung. The ground-glass opacity is associated with interlobular septal thickening, producing polygonal shapes, described as the “crazy paving” pattern. Comparison of HRCT findings in various forms of PAP suggests that autoimmune PAP presents with lower lung predominance (71%), whereas secondary PAP presents with a more even distribution (62%) (9) . The crazy paving pattern is not specific for PAP- a retrospective review of thoracic CT performed in a wide variety of diffuse lung diseases showed that this pattern may be seen in many pulmonary disorders, although all patients with PAP in this study had a crazy paving pattern detectable at HRCT (10).
Pulmonary function tests in patients with PAP show a restrictive pattern and reduced diffusing capacity in a majority of patients (11). Detection of anti GM-CSF antibodies has an excellent sensitivity and specificity for autoimmune variant of primary PAP, but the prognostic value of the presence of these antibodies requires further investigation (12) . Recently, a mucin-like glycoprotein, KL-6, has been proposed as a diagnostic and prognostic marker for PAP. A good correlation between KL-6 and disease severity scores was noted (8) .
Spontaneous remission occurs in 5-10% of patients with PAP (11). Treatment of PAP is usually begun when symptoms impair quality of life, although no clear cut guidelines exist for when treatment should be initiated. Whole-lung lavage is almost always effective for relieving symptoms in patients with PAP, although not widely accessible (13) . The procedure of whole-lung lavage consists of infusing aliquots of warm saline into the non-dependent lung while the dependent lung is ventilated. Fluid is recovered passively or sometimes through application of manual or mechanical chest percussion (14). Significant improvement in lung opacities at imaging, hypoxia, and DLCO may be seen in 84% of patients following the first whole lung lavage procedure (11). Treatment with exogenous GM-CSF is still considered experimental, but studies have shown a positive response to recombinant human GM-CSF therapy in nearly 50% of patients with autoimmune PAP (15, 16) . B-lymphocyte depletion therapy with Rituximab has been described in few patients, with promising results (17) . PAP-related mortality has been noted to be lower in primary than secondary forms of the disease (8% versus 50%, respectively) (18) .
References