A 48-year-old woman presents with a progressing discoloration on her bilateral anterior thighs. She states that “it is extremely cold in my office and I have to warm myself all the time.” She does so by heating hard corn kernel bean bags in a microwave and placing them on her thighs throughout her entire 8-hour workday. The lattice pigmentation has developed over the past 6 months. She denies pain, itching, or blistering. Her medical history is relevant for hypothyroidism.
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Erythema ab igne presents as an area of localized reticulated erythema and hyperpigmentation arising on areas of the body exposed to prolonged heat or infrared radiation. Initially red in appearance, exposed areas subsequently become mottled and acquire shades of brown, blue, or purple.
Historically, the rash was termed “fire stains” as it was correlated with sitting in front of open fires.1 Heating pads, car seat heaters, and even laptops may induce this disorder.2 Erythema ab igne is more common in females and those who experience chronic pain.3
The pathogenesis is not fully understood, although chronic heat and/or infrared radiation will denature DNA within the epidermis and dermis.4 Avoidance of the inciting heat or radiation is necessary to promote resolution and the discoloration will gradually fade over time.
Erythema ab igne is rarely associated skin malignancy; however, both squamous cell carcinoma and Merkel cell carcinoma have been reported to arise in affected areas.5,6
Renaldo Hidalgo, DO, practices Family and Sports Medicine at Allina Health System in St. Paul, Minnesota. Stephen Schleicher, MD, is director of the DermDox Dermatology Centers in Pennsylvania, associate professor of medicine at Geisinger Commonwealth Medical College, and clinical instructor of dermatology at Arcadia University and Kings College.
1. Patel DP. The evolving nomenclature of erythema ab igne-redness from fire. JAMA Dermatol. 2017;153(7):685. doi:10.1001/jamadermatol.2017.2021
2. Salvio AG, Nunes AJ, Angarita DPR. Laptop computer induced erythema ab igne: a new presentation of an old disease. An Bras Dermatol. 2016;91(5 Suppl 1):79-80. doi:10.1590/abd1806-4841.20165139
3. Kettelhut EA, Traylor J, Roach JP. Erythema ab igne. In: StatPearls. StatPearls Publishing; 2021 Jan. Updated 2021 Aug 11. https://www.ncbi.nlm.nih.gov/books/NBK538250/
4. Roth D, London M. Acridine probe study into synergistic DNA-denaturing action of heat and ultraviolet light in squamous cells. J Invest Dermatol. 1977:69(4):368-372. doi:10.1111/1523-1747.ep12510247
5. Sigmon JR, Cantrell J, Teague D, Sanguea O, Sheehan DF. Poorly differentiated carcinoma arising in the setting of erythema ab igne. Am J Dermatopathol. 2013;35(6):676-678. doi:10.1097/DAD.0b013e3182871648
6. Jones CS, Tyring SK, Lee PC, Fine JD. Development of neuroendocrine (Merkel cell) carcinoma mixed with squamous cell carcinoma in erythema ab igne. Arch Dermatol. 1988;124(1):110-113.