Diagnosis: Erythema ab igne
The diagnosis of erythema ab igne (EAI) can be made based on the patient’s history and clinical findings. EAI is a pigmented dermatosis characterized by a reticulated erythema (frequently with telangiectasia) that results from repeated exposure to low-dose infrared radiation.1,2 Most patients have no symptoms, although some may describe a slight burning sensation.3 Whereas mild and transient erythema may follow a single exposure to a dose of infrared radiation that is insufficient to cause a burn, EAI’s more marked erythema with resultant hyperpigmentation requires repeated exposures to a similarly low dose.4 In severe cases, the reticulated pattern may be obliterated by extensive hyperpigmentation with only the periphery of the lesion retaining the characteristic lacy weblike appearance; rarely, subepidermal bullae have been reported.4,5 Isolated cases of cutaneous malignancies, specifically squamous cell and Merkel cell carcinomas, have been reported to arise in lesions of EAI.6,7
Once a common condition typically seen on the lower legs of individuals who spent time in close proximity to a heat source, the incidence of EAI has markedly decreased with the advent of central heating. However, the condition can still be seen in individuals who expose localized areas of their bodies to a heat source. Interestingly, the sources of heat responsible for inducing EAI are reflective of the times and determine the location of the eruption.4 In the past, the disorder had been found on the shins of those who sat in front of open fires or coal-burning stoves; more recently, there is greater anatomic variability with laptop computers, heated furniture, car heaters, hot-water bottles, and heating pads being the reported culprits.1,4,8
Although its appearance is quite characteristic, atypical cases of EAI may be mistaken for such conditions as poikiloderma atrophicans vasculare, livedo reticularis, cutis marmorata, and livedoid vasculitis. If the diagnosis remains uncertain after a comprehensive history and physical examination, a punch biopsy should be obtained. Histopathologic findings include hyperkeratosis, squamous atypia, epidermal atrophy, and dermal elastosis; intact elastic fibers differentiate this condition from solar elastosis. Hyperkeratotic lesions have been described arising in lesions of EAI. Histologically, these lesions closely resemble actinic keratosis and have been referred to as “thermal keratoses.”2 When present, the lesions should be closely monitored because of an increased risk of progression to squamous cell carcinoma.
No definitive therapy is available for EAI. Identification and removal of the heat source is of utmost importance in the treatment of this disorder, as is the correction of such predisposing conditions as cold intolerance associated with hypothyroidism. If interrupted early, the pigmentary changes may be entirely reversible. Furthermore, resolution of histological atypia has been observed following treatment with topical 5-fluorouracil.9 These patients should be closely monitored and further biopsies taken if malignant transformation is suspected. More advanced cases may respond somewhat to tretinoin.8
Shortly before presentation, our patient was diagnosed with hypothyroidism. Levothyroxine was prescribed, and she was advised to stop using the electric heater. Several months later she was euthyroid. The burning sensation ceased over time, and the lesions faded. Her case is still being monitored.
Dr. Chaundhry is a dermatology resident at Eastern Virginia Medical School in Norfolk. Dr. Nunley is professor of dermatology at Medical College of Virginia Hospitals, also in Richmond. Neither author has any relationship to disclose relating to the content of this article.
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- Bilic M, Adams BB. Erythema ab igne induced by a laptop computer. J Am Acad Dermatol. 2004;50:973-974.
- Arrington JH, Lockman DS. Thermal keratoses and squamous cell carcinoma in situ associated with erythema ab igne. Arch Dermatol. 1979;115:1226-1228.
- Shahrad P, Marks R. The wages of warmth: changes in erythema ab igne. Br J Dermatol. 1977;97:179-186.
- Tan S, Bertucci V. Erythema ab igne: an old condition new again. CMAJ. 2000;162:77-78.
- Kokturk A, Kaya TI, Baz K, et al. Bullous erythema ab igne. Dermatol Online J. 2003;9:18.
- 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;124:110-113.
- Hewitt JB, Sherif A, Kerr KM, Stankler L. Merkel cell and squamous cell carcinomas arising in erythema ab igne. Br J Dermatol. 1993;128:591-592.
- Meffert JJ, Davis BM. Furniture-induced erythema ab igne. J Am Acad Dermatol. 1996;34:516-517.
- Sahl WJ Jr, Taira JW. Erythema ab igne: treatment with 5-fluorouracil cream. J Am Acad Dermatol. 1992;27:109-110.
All electronic documents accessed August 15, 2010.