Rare Mimic of Angiosarcoma: Erythema Ab Igne with Reactive Angiomatosis.

Erythema ab igne is an uncommon physical dermatosis that presents with localized patches of reticulated erythema and hyperpigmentation corresponding with the underlying dermal venous plexus. The rash occurs in response to chronic heat exposure that does not meet the threshold for thermal burn of the skin. The histopathologic findings are characterized by atrophy and thinning of the epidermis, focal hyperkeratosis, and keratinocyte atypia. The dermis displays dilated capillaries, evidence of pigment incontinence, and prominent elastotic material. We report a case of a 65-year-old male who presented to his primary care physician with a 1-year history of reticular erythema and hyperpigmentation with focal ulceration on his right lateral leg. Histopathology on biopsy revealed mild hyperkeratosis and focal epidermal atrophy; however, the most striking finding was a proliferation of dermal vascular spaces lined by pleomorphic endothelial cells and numerous mitotic figures, which was morphologically compatible with angiosarcoma. However, clinicopathologic correlation and immunostaining revealed an actual diagnosis of erythema ab igne with reactive angiomatosis. Reactive angiomatosis-morphologically mimicking angiosarcoma-is a rarely reported feature of severe erythema ab igne, and dermatopathologists should be aware of this possibility to avoid misdiagnosis of erythema ab igne as angiosarcoma.