Pulmonary Alveolar Proteinosis (PAP)

Epidemiology and Etiology:

· Rare

· Accumulation of surfactant

· Overproduction of surfactant by type II pneumocytes OR

· Impaired clearance of surfactant by alveolar macrophages

· Comination of the above 2

· Idiopathic usually

· 30-50y

· Occupational

· Dust

· Drug-induced

· Hematologic diseases

· immunodeficiency

Common sites:

·

Gross features:

· Firm yellow-white nodules

· Up to 2cm diameter

· Diffuse

· Mainly perihilar

· Extensive bilateral airspace consolidation

· Thickening of lobular septae

Histologic features:

· intra-alveolar accumulation of lipid-rich eosinophilic material

· pink granular material

· often rim of retraction separates the alveolar wall slightly from the exudates

· embedded clumps of dense globular material

· embedded cholesterol clefts

· not finely vacuolated or foamy (like Pneumocystis)

· relatively few other changes

· may have interstitial fibrosis with long-standing disease

· may have chronic inflammation

· more dramatic inflammatory changes should suggest comorbid infection (ex. Nocardia) or Pneumocystis

Immunophenotype:

Marker:	Sensitivity:	Specificity:
PASD (proteinaceous material)
surfactant

Molecular features:

·

Other features:

·

References:

· Silverberg SG, DeLellis RA, Frable WJ, LiVolsi VA, Wick MR. Silverberg's Principles and Practice of Surgical Pathology and Cytopathology: 2-Volume Set. 4th ed. Churchill Livingstone; 2005:2656.