Pneumocystis Pneumonia : Microscopic Features

Microscopic Features: The air spaces become filled with amorphous, frothy or foamy exudate (alveolar casts) containing organisms. The appearance is similar to alveolar proteinosis but less homogenous. These casts are nicely highlighted by PAS stain in this image. This classic pattern was commonly seen during the HIV epidemic. With the availability of effective treatments for AIDS, pneumocystis pneumonia is now more likely to be encountered in other at-risk groups such as those on long-term immunosuppression or glucocorticoid therapy and the features may be subtle.