Rare Immuno-Induced Keratoacanthomas Showed on 18F-FDG PET/CT in a Metastatic Melanoma Patient

A 76-year-old man managed for stage IV advanced melanoma was treated with nivolumab-ipilimumab, complicated by corticotropic insufficiency, hypothyroidism, and rash. At first evaluation, 18F-FDG PET/CT clearly showed complete metabolic response allowing continued treatment with nivolumab alone. At 6 months, 18F-FDG PET/CT fully confirmed the persistence of complete metabolic response but showed the appearance of cutaneous focal uptakes of both lateral thighs and a cutaneous diffuse uptake on lower limbs. Clinically, he had a severe verrucous lichenoid eruption with eruptive keratoacanthomas, confirmed after resection. We report a case of rare immunotherapy-induced keratoacanthomas first showed by 18F-FDG PET/CT.