The case demonstrates a typical fibrotic hypersensitivity pneumonitis secondary to methotrexate-induced pulmonary drug toxicity. Infection and hypersensitivity pneumonitis secondary to other environmental triggers were excluded clinically and on antigen testing. Symptoms improved with steroids and cessation of methotrexate.

Pulmonary drug toxicity from methotrexate is not uncommon. The exact etiology is uncertain but hypothesized to result from pneumonitis secondary to direct alveolar drug toxicity, hypersensitivity pneumonitis, and superimposed atypical infection from immune suppression. The imaging features of methotrexate pulmonary drug toxicity are variable and can include ground-glass opacities, organizing pneumonia and pleural effusions, in addition to hypersensitivity pneumonitis.