Pembrolizumab-induced severe eczematous dermatitis and the use of methotrexate as a steroid-sparing agent

Immune checkpoint inhibitors, a first-line treatment of metastatic melanoma and other cancers, improve survival but commonly cause immune-related cutaneous adverse events. Early recognition and classification of these adverse events are important for effective management. We present a case of an elderly man with metastatic melanoma who developed a widespread, pruritic grade 3/4 eczematous reaction to pembrolizumab, significantly impacting his quality of life. Following cessation of the pembrolizumab, systemic steroids led to minimal response alongside adverse cushingoid effects. Consequently, immunomodulatory methotrexate treatment was introduced, leading to significant improvement within 3 months. Dry, atrophic skin and purpuric patches secondary to long-term steroid use were noted, so prednisolone was tapered. At 6 months, his skin rash cleared, so methotrexate was discontinued. Importantly, his melanoma remained in remission. This case highlights the importance of a multidisciplinary, stratified approach to the management of immunotherapy-related side effects and the early introduction of steroid-sparing agents to optimise patient care.