Clinical role of FDG PET/CT for methotrexate-related malignant lymphoma

Methotrexate-related malignant lymphoma (MTX-RML) is a type of therapy-related lymphoma, and it often occurs in patients with rheumatoid arthritis. The most distinctive characteristic of MTX-RML is a quick response to withdrawal of MTX. However, because there is a risk of recurrence without a distinctive indicator of disease, close follow-up is needed. We present F-18 2-fluoro-2-deoxyglucose (FDG) postitron emission tomography (PET) or computed tomography (CT) images of MTX-RML along with the characteristic clinical presentation of MTX-RML. FDG PET/CT has the advantage of being able to detect malignant lymphoma in patients who have undergone MTX treatment. After withdrawal of MTX, FDG uptake decreases along with a reduction in the volume of lesions. Although recurrent lesion develops independent to the initial FDG PET/CT findings, FDG PET/CT is useful for early detection of unexpected recurrent lesions. FDG PET/CT allows for the assessment of malignant lymphoma and recurrent lesions in patients who received MTX therapy, which is crucial for the management of MTX-RML.