Fatal mycosis fungoides, misdiagnosed as contact dermatitis.

Background: Mycosis fungoides (MF) is a rare subtype of non-Hodgkin's lymphoma that primarily involves the skin. Its slow progression over several years and diverse clinical presentations-including itchy patches, plaques, or tumors-often lead to initial diagnosis of inflammatory dermatoses such as eczema or psoriasis, making accurate diagnosis challenging.

Case presentation: We present Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) findings of a 61-year-old man with histologically confirmed cutaneous T-cell lymphoma (CTCL), mycosis fungoides (MF). The disease initially manifested as an itching rash on his palms, which gradually progressed over a year to involve his trunk and extremities, ultimately affecting 70% of his body surface area despite multiple treatments, including prednisone, dupilumab, methotrexate, and adalimumab. The patient was initially misdiagnosed and treated for contact dermatitis for three years. After the final diagnosis of MF, his condition continued to deteriorate despite IV antibiotics, palliative radiation, and one cycle of brentuximab vedotin. The patient succumbed to the disease 23 days after the MF diagnosis.

Conclusion: This report highlights the clinical overlap between inflammatory dermatoses and mycosis fungoides and serves as a reminder to clinicians to consider MF in patients with persistent, atypical dermatitis and to employ comprehensive diagnostic tools to guide management.