Pathologic features of the lung in the immunocompromised host

Acute pulmonary disease is a major complication of immunodeficiency, and it has become increasingly important with the expanded use of immunosuppressive drugs. When routine clinical evaluation fails to identify a specific etiologic agent, a morphologic diagnosis is pursued by means of one or more invasive procedures. Interpretation of the material obtained by these procedures poses a challenge to pathologists. In this paper, the important histopathologic patterns of pulmonary disease likely to be encountered in this setting are reviewed, with emphasis on differential diagnosis. In addition, various diagnostic techniques are discussed and compared, with regard to interpretation of findings and diagnostic yields.