The serum LDH is almost always increased. The cause of PAP is unknown. Pulmonary function tests demonstrate a restrictive defect with a decreased diffusing capacity, and hypoxia. The alveoli are filled with eosinophilic, proteinaceous material that shows a positive reaction on PAS staining. The alveolar septa are usually normal or slightly thickened.
Interstitial fibrosis is unusual.
This is sometimes associated with a faint coarse reticulation. High resolution CT demonstrates a panlobular distribution of increased alveolar density with a superimposed reticular pattern.