Supplementary Material for: Novel Clinicopathologic Subungual Angiokeratoma Series Demonstrating Clinical Features Mimicking Nail Unit Melanoma

Introduction: Angiokeratomas are benign vascular tumors that typically present as a hyperkeratotic, red-brown to black papule on the lower extremities. Angiokeratomas in the subungual location are rare, with few reported cases in the literature. Case Presentation: We present three biopsy-proven cases of subungual angiokeratomas with novel clinical features: involvement of the nail bed, clinically mimicking nodular melanoma, and involving a broad age range, with the youngest patient reported at 25-years-old. Symptoms included tenderness and bleeding while the clinical presentations ranged from evenly to irregularly pigmented nodule(s). Histopathology revealed morphologic findings characteristic of angiokeratoma: multiple dilated vascular spaces within the superficial dermis and overlying epidermal hyperplasia. Conclusion: This case series expands the known clinical presentations of nail unit angiokeratomas and emphasizes the importance of including subungual angiokeratoma in the differential diagnosis of pigmented, nodular lesions of the nail unit.