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Pulmonary
alveolar proteinosis is accumulation of surfactant in alveoli. Etiology
is almost always unknown. Symptoms are dyspnea, fatigue, and malaise.
Diagnosis is based on bronchoalveolar lavage, although characteristic
x-ray and laboratory test abnormalities occur. Treatment is with
whole lung lavage. Five-year survival is about 80% with treatment.
Etiology
Pulmonary alveolar proteinosis is most often idiopathic and occurs in otherwise healthy men and women between 30 and 50 yr. Rare secondary forms occur in patients with acute silicosis, Pneumocystis jiroveci infection, hematologic cancers, or immunosuppression by drugs and in patients with significant inhalation exposures to aluminum, titanium, cement, and cellulose dusts. Rare congenital forms causing neonatal respiratory failure also exist. It is unclear whether idiopathic and secondary cases share a common pathophysiology.
Pathophysiology
Impaired alveolar macrophage processing of surfactant due to abnormal granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling is thought to contribute to the disorder, perhaps due to reduced or absent function of the common β chain of the GM-CSF/IL-13/IL-5 receptor on mononuclear cells (present in some children but not in adults with the disorder). Anti–GM-CSF antibodies have also been found in most patients. Toxic lung injury is suspected but not proved in secondary inhalation causes.
Alveoli are filled with acellular lipoprotein surfactant that stains periodic acid–Schiff (PAS) positive. Alveolar and interstitial cells remain normal. Posterobasal lung segments are mostly affected. The pleura and mediastinum are unaffected.
Symptoms and Signs
Most patients present with progressive exertional dyspnea and weight loss, fatigue, malaise, or low-grade fever. Cough, occasionally producing chunky or gummy sputum, occurs but is less common. Clubbing and cyanosis are uncommon. Inspiratory crackles are rare because alveoli are fluid-filled; when crackles are present, they suggest infection.
Diagnosis
Pulmonary alveolar proteinosis is usually first suspected when a chest x-ray is taken for nonspecific respiratory symptoms. The x-ray shows bilateral mid- and lower-lung field opacities in a butterfly distribution with normal hila.
Bronchoalveolar lavage is done. Lavage fluid is milky or opaque, stains PAS-positive, and is characterized by scattered surfactant-engorged macrophages, an increase in T lymphocytes, and high levels of surfactant apoprotein-A. Thoracoscopic or open lung biopsy is done when bronchoscopy is contraindicated or when specimens from lavage fluid are nondiagnostic. Tests typically ordered before treatment begins include high-resolution CT (HRCT), pulmonary function tests, ABGs, and laboratory tests.
HRCT shows ground-glass opacification, thickened intralobular structures, and interlobular septa in typical polygonal shapes (crazy-paving). This finding is not specific, however, as it may also occur in patients with lipoid pneumonia, bronchoalveolar cell carcinoma, and Pneumocystis
jiroveci pneumonia.
Pulmonary function tests show reduction in diffusing capacity for carbon monoxide (DLco) that is disproportionate to the decreases in vital capacity, residual volume, functional residual capacity, and total lung capacity.
Laboratory test abnormalities include polycythemia, hypergammaglobulinemia, increased serum LDH levels, and increased serum surfactant proteins A and D: All are suggestive but nondiagnostic. ABGs may show hypoxemia with mild to moderate exercise or at rest if disease is more severe.
Prognosis
Without treatment, pulmonary alveolar proteinosis remits spontaneously in up to 10% of patients. A single whole lung lavage is curative in up to 40%; other patients require lavage every 6 to 12 mo for many years. Five-year survival is about 80%; the most common cause of death is respiratory failure, typically occurring within the first year after diagnosis. Secondary pulmonary infections with bacterial (eg, Mycobacteria, Nocardia) and other organisms (Aspergillus, Cryptococcus, and other opportunistic fungi) occasionally develop because of impaired macrophage function; these infections require treatment.
Treatment
Treatment is unnecessary for patients without symptoms or for those with only mild symptoms. Whole lung lavage is done in patients with troubling dyspnea by using general anesthesia and a double-lumen endotracheal tube. Lavage of one lung is done up to 15 times with 1 to 2 L saline while the other lung is ventilated. The process is then reversed. Lung transplantation is not done because the disorder recurs in the transplanted lung.
Systemic corticosteroids play no role in management and may increase the risk of secondary infection. The role of GM-CSF (IV or sc) in management remains to be determined. An open-label study showed clinical improvement in 57% of the patients studied.
Last full review/revision May 2008 by Talmadge E. King, Jr., MD
Content last modified May 2008
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