New-onset dermatomyositis in a patient on nivolumab for metastatic melanoma.

We present a case of antitranscriptional intermediary factor 1 gamma positive dermatomyositis in a patient with metastatic malignant melanoma undergoing therapy with nivolumab. The patient was diagnosed with dermatomyositis after presenting with severe dysphagia, proximal muscle weakness and typical cutaneous and histologic findings. Nivolumab was discontinued, and intravenous and oral steroids, intravenous immunoglobulin and rituximab were initiated for the treatment of dermatomyositis. Both paraneoplastic dermatomyositis in patients with metastatic melanoma and dermatomyositis presenting as an immune-related adverse event in patients receiving immune checkpoint inhibitors (ICI) are rare. In this case, we highlight features that are consistent with both paraneoplastic dermatomyositis and ICI-induced dermatomyositis.