Case Report: Localized neutrophilic dermatosis at a split-skin donor site during PD-1 blockade: a unique immune-related adverse event.

The prognosis of melanoma has significantly improved since the introduction of immune checkpoint inhibitor (ICI) therapies. While ICIs are associated with a range of immune-related adverse events (irAEs), these reactions may occur early or late during treatment. Neutrophilic dermatoses, including pyoderma gangrenosum, are commonly observed in patients with systemic inflammatory disease, but have also been reported as rare cutaneous irAEs. To further characterize this rare phenomenon, we present the case of a 45-year-old patient with stage IIB cutaneous melanoma who underwent surgical resection of the primary tumor with split-thickness skin graft coverage, followed by adjuvant therapy with the PD-1 inhibitor nivolumab. During the one-year course of immunotherapy, the donor site of the graft exhibited persistent non-healing and progressive ulceration. However, it did not extend beyond the boundaries of the initial harvest site. Of note, the recipient site at the left heel healed without complications. The lesion was biopsied after completion of immunotherapy. Histopathological analysis revealed a neutrophilic dermatosis with PG-like features. The lesion showed rapid improvement upon initiation of dapsone therapy, which is in line with its action on neutrophils. This case underscores the diagnostic challenge posed by atypical cutaneous irAEs, particularly when localized and lacking systemic features. Awareness of such rare presentations is crucial to enable timely recognition and appropriate treatment.