Pulmonary Alveolar Proteinosis (PAP)

Fig.1: Chest radiograph of a 44-year-old immunocompetent woman with subacute dyspnea, short of breath and no fever shows diffuse, bilateral opacities predominantly in the perihilar and mid-to-lower lungs. Note normal-sized heart.
Fig.2: Axial CT of the chest shows extensive bilateral ground-glass opacities superimposed with interlobular septal thickening (arrows) in the upper, middle and lower lobes. There is no pleural effusion.

Clinical Features

• Rare disorder
  
• Lipoprotein material (probably surfactant) accumulates in alveoli
  
• Congenital, secondary (to impaired alveolar macrophage numbers or function i.e. immunosuppression, hematologic malignancy, inhaled silica, etc) and acquired forms
  
• Men > women, median age at diagnosis = 39 years
• Most common presenting symptom = progressive exertional dyspnea and cough
  
• Susceptibility to pulmonary infections (possible opportunistic organisms)
• Lavage Fluid: large and foamy alveolar macrophages + diffuse eosinophilic bodies on a PAS-stained background
  
• Gold standard: open-lung biopsy

Imaging Appearance

• Chest radiograph: bilateral airspace disease with perihilar predominance ("bat wing" appearance) but without signs of left-sided heart failure
• CT: ground-glass opacifications with superimposed interlobular septal thickening and intralobular lines "crazy paving".
  

Reference:

Trapnell BC, et al. Pulmonary Alveolar Proteinosis. N Engl J Med 2003 (December 25)