Drug- and therapy-induced lung injury

Drug-induced lung disease represents one of the more challenging areas of pulmonary medicine from both a clinical and pathological standpoint. Over 300 agents are associated with adverse pulmonary reactions and the list is continually expanding. Clinically, drug-induced pulmonary disease may manifest as an acute, subacute or chronic reaction. An acute reaction occurs within minutes or hours following exposure. Anaphylaxis, bronchospasm and pulmonary edema are examples of such acute reactions. Subacute reactions occur days to weeks following administration and chronic reactions manifest months to years after initiation of a particular drug. Complicating the picture are drug reactions presenting as an acute lung disease in patients who have taken a drug for years. Additionally, drug reactions may occur after discontinuation of a drug, most notably exemplified by bischloroethyl nitrosourea (BCNU) therapy, in which the drug has been implicated in pulmonary disease years after discontinuation. Clinical diagnoses of drug toxicity require a high index of suspicion, given that presenting symptoms are not specific and overlap with numerous other pulmonary diseases. Further confounding the picture, a patient may have multiple factors which could potentially contribute to the development of pulmonary disease (e.g. a patient with rheumatoid arthritis on methotrexate or an immunosuppressed patient on chemotherapy). Radiographic findings similarly tend to reflect the wide range of histological findings associated with drug toxicity and are typically not specific by themselves.