Delayed eosinophilic fasciitis following adjuvant pembrolizumab for renal cell carcinoma: a case report

Background Immune checkpoint inhibitors (ICIs) have significantly improved survival outcomes in various malignancies, including renal cell carcinoma (RCC). Pembrolizumab, an anti-PD-1 monoclonal antibody, is an established adjuvant therapy for high-risk localized RCC. However, ICIs are associated with a unique spectrum of immune-related adverse events (irAEs). Cutaneous irAEs are common, but eosinophilic fasciitis (EF), a rare scleroderma-like disorder characterized by symmetrical painful swelling, progressive induration of the skin and soft tissues, and peripheral eosinophilia, remains an infrequent and often under-recognized complication. A particularly challenging aspect is the occurrence of delayed immune-related events (DIRE), which manifest after the cessation of immunotherapy. Case presentation We report the case of a 61-year-old male who developed progressive diffuse muscle stiffness, cutaneous tightness, and marked peripheral eosinophilia five months after completing adjuvant pembrolizumab for high-risk localized clear cell RCC. The patient had previously experienced grade 3 immune-mediated hepatotoxicity near the end of his adjuvant treatment, leading to pembrolizumab discontinuation. Despite initial differential diagnoses including parasitic infection, a full-thickness skin and fascia biopsy confirmed eosinophilic fasciitis, revealing characteristic inflammatory infiltrates in the deep fascia with sparing of the epidermis and superficial dermis. The patient was refractory to initial systemic corticosteroids but was successfully managed with rituximab, achieving significant clinical and laboratory improvement. Conclusions Delayed eosinophilic fasciitis can occur after adjuvant pembrolizumab. In patients with prior immune checkpoint inhibitor exposure who develop progressive skin tightening, musculoskeletal stiffness, and eosinophilia, prompt multidisciplinary assessment and full-thickness biopsy can facilitate timely diagnosis and management.