Variant alveolar lipoproteinosis: a syndrome with distinct clinical and pathological features

Pulmonary alveolar proteinosis (PAP) is a rare condition in which pulmonary macrophages fail to clear surfactant, resulting in the alveolar accumulation of lipoproteinaceous debris. The histopathology of PAP is typified by diffuse filling of terminal airways with eosinophilic, PAS/diastase (PAS/D)-positive acellular material. We present five patients who showed histopathological changes in the lungs consistent with mild PAP. However, these cases were notable for the abundance of degenerating alveolar macrophages, weak PAS staining of lipoproteinaceous material and paucity of lamellated bodies on ultrastructural examination. Only one patient showed the CT finding of mosaiform 'crazy-paving' and the opalescent bronchoalveolar lavage fluid characteristic of PAP. In one case, therapeutic lung lavage based on a presumptive diagnosis of PAP exacerbated respiratory distress. Three patients showed partial or near-complete resolution of disease in response to high-dose corticosteroid therapy, a treatment approach that is generally ineffective in PAP. We conclude that distinguishing 'variant alveolar lipoproteinosis' from classical PAP is clinically important. Despite the otherwise typical appearance of lipoproteinaceous alveolar material in lung biopsies, the presence of degenerating foamy macrophages and atypical histochemical, ultrastructural and radiographic features suggest a steroid-responsive form of proteinosis that is likely pathogenetically distinct and may not be amenable to whole-lung lavage.