Deceptive Hypermetabolic Cutaneous/Subcutaneous Manifestations in a Melanoma Patient Post Nivolumab Immunotherapy on 18F-FDG PET/CT Scan

Immune-related adverse events are crucial considerations when interpreting 18 F-FDG-PET/CT scans for assessing immunotherapy response. We describe a 60-year-old woman with stage III melanoma involving the left middle finger and a regional lymph node, treated with immunotherapy. Follow-up 18 F-FDG PET/CT after 5 cycles of nivolumab revealed innumerable new hypermetabolic cutaneous and subcutaneous nodules that were clinically palpable, in addition to new avid bilateral hilar and mediastinal lymph nodes. After 1 month of oral corticosteroid therapy, the PET/CT scan showed complete resolution of these findings. Six weeks later, the skin nodules recurred mostly on the extremities, and biopsies from arm lesions showed benign granulomatous changes.