Bilateral Diffuse Uveal Melanocytic Proliferation in a Woman with Metastatic Scalp Squamous Cell Carcinoma Treated with Cemiplimab

Bilateral diffuse uveal melanocytic proliferation (BDUMP) is a rare paraneoplastic intraocular syndrome that causes progressive visual loss in patients driven by an IgG factor associated with an underlying malignancy. The IgG factor − cultured melanocyte elongation and proliferation − was found in the IgG fraction of the serum of BDUMP patients. It has been shown to be involved in melanocytic proliferation. In this case report, we describe the first case of BDUMP related to metastatic cutaneous squamous cell carcinoma (cSCC) of the scalp. A 61-year-old woman complained of decreased vision in both of her eyes, while being treated with cemiplimab (an anti-PD-1 therapy) for metastatic cSCC. Fundus examination showed hypopigmented lesions in a leopard pattern and pigmentary clumps in both eyes. Further imaging confirmed the diagnosis of BDUMP. The patient was successfully treated with plasmapheresis. During follow-up, cataract progressed in both eyes, and she underwent cataract surgery with visual acuity improvement to 20/20. BDUMP is a challenging diagnosis especially in patients treated with anti-PD-1 immunotherapy as it can be confused with drug-related effects. It is crucial to distinguish between the cases in order to allow the appropriate treatment which includes continuation of systemic anti-PD-1 for the underlying malignancy and plasmapheresis therapy for BDUMP.