Abstract
Pulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by progressive
accumulation of surfactant in pulmonary alveoli, resulting in hypoxemic respiratory
insufficiency and an increased risk of secondary infections and pulmonary fibrosis.
Secondary PAP (sPAP) occurs because of an underlying disease that reduces the number
and/or functions of alveolar macrophages, with hematological disorders being the commonest
underlying cause. sPAP accounts for 4% of PAP cases, often occurs in the fourth decade
of life, and has a slight male predominance. Patients with sPAP often present in the
context of their underlying clinical condition. The prognosis of sPAP is considerably
worse than aPAP, with an estimated median survival of less than 20 months. Given the
nonspecific clinical presentation of PAP, its diagnosis requires appropriate serological,
radiological, and bronchoscopic evaluation. The characteristic “crazy-paving” appearance
described in aPAP might not always be present in sPAP. Ground glass opacifications
in sPAP typically show a more diffuse pattern compared with a patchy geographic pattern
seen in aPAP. The only proven therapy for sPAP is the treatment of the underlying
disease, with whole lung lavage demonstrating efficacy in a small number of cases.
In this review, we discuss the presentation, prognosis, and treatment of sPAP.
Keywords
secondary PAP - proteinosis - pulmonary alveolar proteinosis - lipoproteinosis - macrophage
