Respiratory Tract Diseases That May Be Mistaken for Infection

The differential diagnosis of lung infiltrates in transplant patients includes non-infectious processes that may mimic pneumonia. Hydrostatic and non-cardiogenic pulmonary edema, as well as transfusion-related lung injury, may cause bilateral airspace opacification that may be confused with an infectious process. Chemotherapeutic agents, whether administered for treatment of an underlying hematologic malignancy, for induction prior to transplant, or for the treatment of GVHD or graft rejection after transplant, may cause lung injury that in some cases may not become apparent until years later. Radiation-induced lung injury may cause a distinct pattern of lung injury, which may present months after exposure. In hematopoietic stem cell transplant patients, pulmonary diagnoses such as engraftment syndrome, idiopathic pneumonia syndrome, and diffuse alveolar hemorrhage can mimic pneumonia. After lung transplantation, infiltrates may be seen as a consequence of primary graft dysfunction or allograft rejection. Organizing pneumonia may be seen both in recipients of solid organ and hematopoietic stem cell transplants. Organizing pneumonia may be cryptogenic or associated with the use of the mTOR inhibitor sirolimus. Failure to accurately diagnose non-infectious infiltrates may lead to unnecessary antibiotic treatment and failure to address the underlying pathophysiologic process.