Erythema Ab Igne (EAI) is a persistent form of erythema manifesting as reticulated residual pigmentation resulting from long exposures to excessive heat without producing frank burning of the skin. It begins as a mottling caused by local hemostasis and becomes a reticulated erythema evolving into residual pigmentation. Multiple colors are simultaneously present in active patches varying from pale pink to rose or dark purplish brown coloration. Once the source of heat exposure is removed the affection tends to disappear gradually, however, the pigmentation is permanent.
Erythema Ab Igne in olden days was most frequently found on the legs, related to warming in front of fireplaces. Modern day causes include space heaters and car heaters. Involvement of the lower back is usually caused by use of electric heating pads. Heating pads and use of laptop computers resting on the thighs can induce EAI. It has also been reported to involve the posterior thighs in patients that frequently use heated car seats. Occupational causes have been reported in cooks, silversmiths and other professions that require long periods of exposure to direct moderate heat.
Patients that continue to experience heat exposure for long periods are at risk of developing Bowen’s disease, squamous cell carcinoma (SCC) and Merkel cell carcinomas. Bowen’s disease and SCC often respond to 5-fluorouracil (5-FU), imiquimod or photodynamic therapy. Merkel cell carcinomas are often very aggressive and require wide local excision and possible radiation therapy.
TREATMENT: Use of emollients containing alpha-hydroxy acids, 4% hydroquinone, and tretinoin 0.05% may help in reducing the unsightly pigmentation. Use of Q-switched neodymium-doped yttrium-aluminum-garnet (Nd:Yag) laser may also be effective. To read more about Erythema Ab Igne click HERE, HERE and HERE.