Widespread Rash on Abdomen

Erythema ab igne (EAI), also known as toasted skin syndrome, presents as a reticulated, erythematous or hyperpigmented rash. Erythema ab igne is Latin for “redness by fire.” It is most commonly observed in people who spend extended periods of time...

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Erythema ab igne (EAI), also known as toasted skin syndrome, presents as a reticulated, erythematous or hyperpigmented rash. Erythema ab igne is Latin for “redness by fire.” It is most commonly observed in people who spend extended periods of time in close proximity to heat sources.¹ In India and China, this rash was historically seen in individuals who carried hot coals under their shawls or slept on beds of heated bricks in order to keep warm during the winter months. ¹ Today, heat sources such as heating pads and laptops are often implicated in EAI. EAI is more common in females than in males and the anterior leg is the most common location.²

EAI occurs secondary to chronic exposure to sub-threshold levels (43°C to 47°C) of infrared radiation. The temperature is high enough to cause EAI but not burns.^3,4 The pathogenesis is uncertain, but the reticulated pattern likely corresponds to vasodilation of the dermal venous plexus with extravascular deposition of hemosiderin.⁵ Laptop computers, heating pads, cell phones, heated chairs, car heaters, hot water bottles and electric space heaters are all potential heat sources that can contribute to the development of EAI. The anatomic site of EAI can be an important clue in identifying the culprit heat source.¹ Heating pads tend to cause EAI in the lower back or abdominal region, depending on the reason for their use. Patients with sickle cell disease, gastrointestinal pathology, spinal disc prolapse, and cancer may use heat as an analgesic, which can increase their risk for EAI. Cellphones in pant pockets can lead to anterior thigh or buttock EAI. Laptop computers tend to cause EAI on the anterior thighs. Certain occupational exposures can also increase the risk of EAI: bakers, fast food workers with exposure to infrared heat lamps, and metal foundry workers are especially susceptible. Rarely, hypothyroidism may lead to a generalized form of EAI due to extended hot showers.¹ Cultural practices such as cupping and moxibustion may also cause EAI. Finally, medical warming devices and lasers are some notable iatrogenic causes.¹

EAI begins as a blanching, erythematous, reticulated patch that resolves within hours of withdrawing the heat source. With chronic exposure, hyperpigmentation, hyperkeratosis, overlying telangiectasia, and sometimes bullae may develop. Patients might experience pruritus or a mild burning sensation, but more commonly EAI is asymptomatic.¹ The differential diagnosis includes cutis marmorata, livedo reticularis, livedo racemosa, and cutaneous COVID-19.^1,2 Livedo reticularis is associated with connective tissue disease and vasculopathies including systemic lupus erythematosus and cryoglobinemia; it occurs with cold rather than heat exposure. Livedo racemosa presents as broken, circular net-like patches, and it has a more irregular appearance than livedo reticularis. Unlike livedo reticularis, it does not usually resolve on warming. Cutis marmorata is a fine reticular rash seen in newborns which also tends to resolve on warming. A more serious variant called cutis marmorata telangiectasia congenita appears like cutis marmorata but does not resolve on warming and warrants further workup as it may be associated with congenital syndromes and limb growth abnormalities.¹ Finally, cutaneous COVID-19 can present in a reticular pattern that resembles livedo reticularis. Other differential diagnoses may include livedoid vasculitis, poikiloderma of Civatte, cutaneous T-cell lymphoma, dermatomyositis, angiosarcoma, vasculitis, and bullous disorders.^1,2,5

The diagnosis is clinical and is ascertained from the history and physical exam.¹ A history of chronic heat exposure is usually identified. Dermoscopy reveals telangiectasias and white scaling.⁶ A biopsy may be performed if the clinician is uncertain or if there is concern of malignant transformation.¹ On histopathologic examination, dilated vascular channels, interface dermatitis, and melanin incontinence are seen, which are grossly consistent with reticular rash, erythema, and hyperpigmentation respectively.^3,7

The first step after diagnosis is to identify and eliminate the culprit heat source. The rash will then gradually resolve over months to years. Many patients, especially patients with skin of color, suffer from hyperpigmentation. Topical treatments used in melasma such as hydroquinone and tretinoin may be used to lighten the skin. If the patient has hyperkeratosis, 5-fluorouracil may be used.¹ Finally, Nd:YAG laser therapy may be another alternative⁸, however, caution must be exercised in patients with skin of color due to a higher risk of laser-induced hyperpigmentation.

The prognosis of EAI is usually excellent. However, EAI can rarely be associated with an increased risk of squamous cell carcinoma after a prolonged latency period (years).⁵ Merkel cell carcinoma and marginal zone lymphoma have also been reported.^6,9,10 Hence, in patients with a long history of EAI, dermatologic evaluation for cutaneous malignancy is essential. 

The patient in this case was diagnosed with erythema ab igne based on history and physical exam, and was advised to avoid using heating pads. For the erosions, liberal application of petrolatum was recommended. She will follow up with a dermatologist for regular skin cancer screenings. 

Talia Noorily, MD, is a dermatology resident at Baylor College of Medicine. Rishabh Lohray is a medical student at Baylor College of Medicine in Houston, Texas, and an MBA student at Rice University.

References 

1. Harview CL, Krenitsky A. Erythema ab igne: a clinical review. Cutis. 2023;111(4):E33-E38. doi:10.12788/cutis.0771
2. Ozturk M, An I. Clinical features and etiology of patients with erythema ab igne: a retrospective multicenter study. J Cosmet Dermatol. 2020;19(7):1774-1779. doi:10.1111/jocd.13210
3. Bachmeyer C, Bensaid P, Bégon E. Laptop computer as a modern cause of erythema ab igne. J Eur Acad Dermatol Venereol. 2009;23(6):736-737. doi:10.1111/j.1468-3083.2009.03205.x
4. Bilic M, Adams BB. Erythema ab igne induced by a laptop computer. J Am Acad Dermatol. 2004;50(6):973-974. doi:10.1016/j.jaad.2003.08.007
5. Kozera EK, Sebaratnam DF. Erythema ab igne. Med J Aust. 2021;215(9):405. doi:10.5694/mja2.51292
6. Errichetti E, Stinco G. Dermoscopy in general dermatology: a practical overview. Dermatol Ther (Heidelb). 2016;6(4):471-507. doi:10.1007/s13555-016-0141-6
7. Pincelli T, Keeling J, Sokumbi O. Bullous erythema ab igne unexpected biopsy: challenge. Am J Dermatopathol. 2022;44(8):e86-e87. doi:10.1097/DAD.0000000000002243
8. Kim HW, Kim EJ, Park HC, Ko JY, Ro YS, Kim JE. Erythema ab igne successfully treated with low fluenced 1,064-nm Q-switched neodymium-doped yttrium aluminum garnet laser. J Cosmet Laser Ther. 2014;16(3):147-148. doi:10.3109/14764172.2013.854623
9. 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.
10. Wharton J, Roffwarg D, Miller J, Sheehan DJ. Cutaneous marginal zone lymphoma arising in the setting of erythema ab igne. J Am Acad Dermatol. 2010;62(6):1080-1081. doi:10.1016/j.jaad.2009.08.005