Pulmonary Alveolar Proteinosis (PAP), first described by Rosen and Castleman in 1958, is a rare syndrome characterized by the intra-alveolar accumulation of surfactant lipids and proteins, leading to impaired gas-exchange and resulting in progressive respiratory insufficiency. The current knowledge about PAP is based on small series and individual case reports. While data from these studies have been synthesized into a comprehensive review in 2002, these data represent cases across nearly half a century. However the incidence, prevalence and the natural history of primary PAP have been recently assessed in a large cohort study of PAP patients in Japan, showing differences in some respects with previous published data. If these differences are due to ethnic backgrounds, it could be explained only through a large cross-sectional study that evaluates geographically distributed, ethnically diverse groups of patients.
PAP is recognized to occur in four distinct clinical forms: primary, secondary, congenital and idiophatic, or PAP-like.