"Fatty Lungs": A Uncommon Case of Autoimmune Pulmonary Alveolar Proteinosis

Pulmonary Alveolar Proteinosis (PAP) is a rare lung disease characterized by excessive accumulation of surfactant lipids and proteins in alveoli and terminal airways. It is caused by impaired GM-CSF signaling [1]. Surfactant is synthesized and secreted by alveolar type II epithelial cells, and removed by uptake and catabolism by these cells, and the alveolar macrophages. Patients with PAP usually describe gradual onset of progressive exertional dyspnea and non-productive cough. However, an asymptomatic presentation is observed in up to 25% of cases, even in the presence of diffuse radiographic changes. Three recognized subtypes exist. Autoimmune PAP is associated with neutralizing GM-CSF autoantibodies and accounts about 90% of cases. Secondary PAP may occur in the context of any disease that reduces the abundance or functionality of alveolar macrophages, resulting in impaired surfactant clearance. Congenital PAP is the result of genetic mutations that disrupt GM-CSF signaling, including mutations in the αor β-chains of the GM-CSF receptor [1-3].