Fig. 12.

Methotrexate-induced acute hypersensitivity pneumonitis. 56-year-old woman who was started on methotrexate few weeks prior to presenting with worsening dyspnea. CT. Bilateral poorly defined ground-glass attenuation (arrows). Differential diagnosis includes RA-related interstitial lung disease, opportunistic infection, and adverse drug reaction. Radiologic abnormality and symptoms resolved following withdrawal of methotrexate.

Teaching point: Drug toxicity may mimic infection. Temporal association with treatment history helps in making a diagnosis.