[Pulmonary alveolar proteinosis].

T wenty-four years ago, Rosen et al’ described the entity they called “pulmonary alveolar proteinosis” (PAP). The characteristics ofthis lung disease were that alveoli were filled with granular proteinaceous material which was periodic acid Schiff-positive and that the alveolar septae were relatively normal except for increased numbers of cuboidal “septal cells” (type 2 pneumocytes) in the alveolar lining. They noted very little inflammatory response to this process in the lung and few macrophages in the alveoli. The pathologic description was remarkably accurate and complete, and except ftr ultrastructural descriptions, little new information has been added. Rosen and colleagues believed that most ofthe intraalveolar granular material was derived from the proliferating septal cells that sloughed into the alveolar spaces and underwent degeneration. These investigators were aware of the significant lipid content of the intra-alveolar material. They thought this was either a new disease or a very rare lung disorder that was increasing in incidence. However, relatively few cases have materialized, and PAP remains uncommon. In fact, many people believe PAP is becoming even more uncommon, although there are no epidemiologic data to support such a view. This perception may be only an aberration created by changes in referral patterns as a result of the ever-increasing number of well-trained pulmonologists in the private sector of medicine. However, infbrmation regarding the incidence and distribution of cases of PAP could be useful in investigating the etiology of this disease. Correlating peaks of incidence with clusters of cases of PAP, along with various environmental conditions and infectious epidemics, might give important clues regarding the cause, which is the greatest gap in our knowledge of PAP at this time. Understanding more about the cause of PAP could also further our understanding of the lungs’ response to injury and the kinetics of various types of lung cells. The specfficity of the PAP response has been questioned because ofsimilar pathologic findings in experimental animals and in humans exposed to silica dust,4 in immunosuppressed patients with hematologic disorders,5 and in rats fed ipnndole,6 and because hyperplasia of type 2 alveolar epithelial cells occurs as an element of the reparative process of the lung after various types of injury.79 However, these findings may not be a good argument fbr the nonspecificity of the PAP reaction in the lung, as shown by the report ofSingh et al.’#{176} With the use of specific immunologic staining of surfactant apoprotein, these authors demonstrate that histologic appearance and periodic acid-Schiff staining of intraalveolar granular material are not sufficient to establish the diagnosis of PAP The intra-alveolar proteinaceous material from patients with PAP and no other associated disease stained densely and uniformly for surfactant apoprotein, whereas the intra-alveolar material of patients with PAP-like histologic appearance of the lung who also had leukemia or lymphoma did not. The lung sections from patients with PneumocytLi carinii pneumonia also show !bcal rather than uniform staining fbr surfactant apoprotein. This study not only suggests that PAP may be more specific than has generally been thought, but also raises questions regarding the true incidence of PAP for many of the reported cases have been associated with illnesses.3 With this type of diagnostic aid, more meaningful epidemiologic studies could be performed with the hope of producing information about the etiology of PAP. I. Ode Harris, M.D., FC.C.P Gainesville, FlOrida