A 40-year-old immunocompromised patient develops bilateral pneumonia with diffuse alveolar damage (DAD) pattern on lung biopsy. Viral inclusions are identified — large eosinophilic intranuclear inclusions surrounded by a clear halo ('owl eye') in enlarged cells. What is the organism and the mechanism of DAD in this setting?
- A RSV infection; syncytia formation causing bronchiolar obstruction
- B CMV pneumonitis; direct cytopathic effect plus immune-mediated alveolar injury ✓
- C HSV pneumonitis; Cowdry A inclusions in alveolar cells
- D Adenovirus pneumonia; smudge cells in alveolar exudate
Explanation
The characteristic 'owl-eye' appearance — large intranuclear eosinophilic inclusion surrounded by a clear halo, in cytomegalic (enlarged) cells — is pathognomonic of CMV. CMV pneumonitis causes DAD through direct cytolytic infection of alveolar epithelial cells (type II pneumocytes, endothelial cells) and indirect immune-mediated injury via NK and CD8+ T cell responses. In immunocompromised patients, uncontrolled CMV replication leads to hyaline membrane formation. HSV shows Cowdry A inclusions but without cytomegaly. Adenovirus pneumonia shows 'smudge cells' with ground-glass basophilic intranuclear inclusions.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.