Cutaneous reactive angiomatosis occurring in erythema ab igne can cause atypia in endothelial cells: Potential mimic of malignant vascular neoplasm

Erythema ab igne (EAI), an old and rare disease, is an erythematous, often pigmented, reticular, macular dermatosis that occurs at the site of repeated exposure to moderate heat. Reported herein is an unusual case of EAI occurring in a 33‐year‐old woman with a very broad lesion of reticular erythema and pigmentation on the lower extremities. The patient frequently put her lower extremities close to a heater in the wintertime to alleviate chill. The lesion started a decade ago, and it gradually became conspicuous. Microscopic findings showed a proliferation of small blood vessels in a thickened papillary dermis, not as typical as seen in EAI, but as seen in cutaneous reactive angiomatosis. They were arranged as small lobules and associated with hyalinization, edema and delicate fibroplasia. Many vessels were lined by plump endothelial cells, some of which had enlarged hyperchromatic nuclei. Many of these cells were multinucleated. Similar‐appearing cells were associated with concentric foci of hyalinization without vascular lumina. A few atypical mitoses were observed. The lesion became much less conspicuous after the patient started avoiding close exposure to a heater, without any other special treatments. The aforementioned changes may be confused with malignant vascular neoplasm because of unusual cytological atypia and atypical mitoses in the endothelial cells.