Pulmonary malacoplakia associated with Rhodococcus equi infection in a patient with acquired immunodeficiency syndrome.

Pulmonary malacoplakia associated with Rhodococcus equi, an opportunistic Gram-positive coccobacillus, is unusual. Although this patient is the ninth reported to have pulmonary malacoplakia, he is only the third patient with the acquired immunodeficiency syndrome who has been reported to have pulmonary malacoplakia associated with R equi infection. The patient was a 49-year-old man infected with the human immunodeficiency virus who on initial examination was found to have cavitary pneumonia in the right upper lobe of the lung. Histologic examination of an open-lung biopsy specimen revealed sheets of foamy intraalveolar macrophages that contained coccobacillary organisms and some "targetlike" cytoplasmic inclusions. Electron-microscopic studies showed Michaelis-Gutmann bodies, some of which contained residual bacterial fragments. Cultures of the lung tissue, urine, and blood yielded growth of Gram-positive coccobacilli subsequently identified as R equi. In immunocompromised patients, the possibility of malacoplakia should be considered in the differential diagnosis of diffuse pulmonary infiltrate composed of foamy intraalveolar macrophages.