Acute respiratory distress syndrome precipitated by granulocyte colony-stimulating factor in undiagnosed Pneumocystis jirovecii pneumonia.

We present the case of a 62-year-old man with rheumatoid arthritis who developed a leukaemoid reaction and acute respiratory distress syndrome (ARDS) following granulocyte colony-stimulating factor (G-CSF) administration that had been given to treat neutropenia secondary to methotrexate and leflunomide toxicity. Later it was established that he had Pneumocystis jirovecii pneumonia, which was treated to complete resolution with a course of corticosteroids and antibiotics. This case highlights the potential risk of G-CSF administration in an immune compromised individual in the midst of bone marrow recovery in the context of active infection. Recognition of immune escape syndromes is vital and requires an understanding of potential triggers and risk factors.