[18F]FDG PET/CT in a Case of Mycosis Fungoides Showing an Unusual Adverse Reaction to Mogamulizumab: Correlation Between Imaging and Histological Findings

A 73-year-old female patient, affected by mycosis fungoides (MF), discontinued mogamulizumab, after initial clinical benefit, due to the onset of generalized erythema. Follow-up positron emission computed tomography (PET/CTs) carried out at 3 weeks and 6 months after therapy discontinuation showed, with respect to baseline PET/CT scan, a progressively increasing number of hypermetabolic enlarged lymph nodes suspected for a neoplastic involvement, but with histology indicative of an inflammatory reaction. After sequential therapy with corticosteroids and methotrexate, a complete remission was registered at 18F-fluorodeoxyglucose ([18F]FDG) PET/CT performed at 12 months after mogamulizumab interruption. The case we describe highlights the usefulness of serial examinations with [18F]FDG PET/CT in an MF patient presenting an unusual adverse reaction to mogamulizumab.