A rare case of seminal vesicle involvement by nodal and extra nodal diffuse large B-cell lymphoma, R-CHOP treatment resulting in complete response.

End of treatment PET/CT with low-dose CT reveals pulmonary findings compatible with hypersensitivity pneumonitis, worrisome for Rituximab induced interstitial lung disease (R-ILD). At the time of end of treatment PET/CT there was ongoing antibiotic therapy for febrile neutropenia. 

Due to the pulmonary findings the patient was started on high-dose corticosteroid regime in addition to antibiotics.

Patient age, time of onset of symptoms and radiological changes as well as the intense FDG-uptake in the pulmonary changes are all favoring R-ILD. The patient passed away before definite diagnosis of the pulmonary findings could be established.

This case highlights the diagnostic value of FDG-PET/CT in fever of unknown origin (FUO) and exemplifies the use of the international consensus on FDG-avid lymphomas (Deauville 2009 - Lugano 2014) in initial staging as well as assessment of interim (iPET) and end of therapy (ePET) treatment response.