Pneumocystis infection masquerading as diffuse alveolar damage. A potential source of diagnostic error

The nonspecific histopathologic changes of diffuse alveolar damage (DAD) were the only findings in nine of 17 lung biopsy specimens containing Pneumocystis carinii infection. Because of the frequent absence of the classically described intra-alveolar frothy material, special stains for organisms should be performed on all biopsy specimens from immunocompromised patients that show DAD, and the diagnosis of Pneumocystis infection should not be discarded unless careful search for organisms using special stains is negative.