Methotrexate-induced pneumonitis (MTX-P) is an uncommon side effect of the medication methotrexate that usually appears as interstitial lung disease (ILD). Early detection of the consequence was considered important since stopping MTX, with or without steroid treatment, frequently led to a quick recovery. A delay or misdiagnosis, on the other hand, resulted in death. Because underlying disorders that led to methotrexate treatment, such as rheumatoid arthritis (RA), and opportunistic infections caused by drug-induced immune dysfunction could both cause an ILD, the diagnostic workup might be difficult. Bronchoalveolar lavage (BAL) was used to rule out infectious pathogens, especially in febrile patients, or to screen for malignant cells in the clinical situation. Unfortunately, there were no distinguishing characteristics in BAL that allowed doctors to distinguish MTX-P from RA-associated ILD. Researchers provided two confirmed examples of MTX-P in patients with RA.
Although BAL differential cell counts and alveolar CD4/CD8 values were found to be consistent with those described in the literature, an increase in mast cells and the presence of foamy macrophages had never been observed in previously published cases. Although the presence of both mast cells and foamy macrophages helped identify MTX-P from several drug-unrelated ILDs, it might not help separate MTX-P from Pneumocystis jiroveci pneumonia or RA-associated bronchiolitis obliterans organizing pneumonia.
Reference:journals.lww.com/clinpulm/Abstract/2013/09000/Alveolar_Foamy_Macrophages_and_Mast_Cells_in.3.aspx
