Erythema ab igne induced by a laptop computer

Erythema ab igne (EAI) is a reticular, telangiectatic, pigmented dermatosis occurring after long-term exposure to infrared radiation that is insufficient to produce a burn.1, 2 We present an unusual case of laptop computer-induced EAI.

A 50-year-old white man presented with a 2-week history of an asymptomatic patch on his left leg. On physical examination, there was a fairly well-defined, brown, mildly erythematous, reticulated patch on the left anterior thigh (Fig 1). This asymptomatic eruption was noticed 2 weeks after the patient purchased a new laptop computer. The patient is a systems analyst who spends a considerable amount of time each day using his computer. He frequently placed the computer on his anterior thighs while at work. He stopped resting the computer on his thighs after he repeatedly experienced discomfort from heat emitted from the base of the laptop.

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Fig 1. Erythema ab igne on the left anterior thigh.

The lesion was isolated to the left anterior thigh, because the heat source (optical drive) was located on the left base of the computer. EAI often begins as mild localized erythema. Repeated exposures to moderate heat may result in reticulate erythema, hyperpigmentation, telangiectases, scaling, and atrophy3; subepidermal bullae have also been reported.4

Historically, EAI was commonly seen on the shins of those who worked in front of open fires or coal stoves. EAI may appear on the exposed skin of individuals who sit too close to fireplaces, space heaters, steam radiators, and wood-burning stoves.5 It is also seen after repeated application of hot water bottles and heating pads used to treat ailments such as abdominal pain and chronic back pain.5, 6, 7, 8, 9 Furniture with a built-in heating unit,10, 11 a car heater,12 and a heating blanket13 are additional reported sources of EAI.

Histopathologic changes include hyperkeratosis, epidermal atrophy, squamous atypia, and interface dermatitis with necrotic keratinocytes. An increased amount of dermal elastic tissue may also be seen.14 Histologically, EAI is similar to actinic keratosis, and these lesions have therefore been called “thermal keratoses.”15 The similarities between actinic and thermal keratosis suggest that heat may induce epithelial changes as a result of clonal mutation in the same way that ultraviolet light produces epithelial changes.16 Rare cases of squamous cell carcinoma (SCC) and Merkel cell carcinoma arising in lesions of EAI have been reported.17, 18, 19 Thermally induced cancers are usually SCCs and occur even after 30 years.20, 21

This case illustrates an unusual modern demonstration of EAI. It is important for physicians to be aware of the new and evolving heat sources causing thermal-related cutaneous injury. Patients should be instructed to discontinue close contact with sources of infrared radiation. A biopsy should be performed if there is any evidence of cutaneous malignancy. 5-Fluorouracil cream has been reported to clear epithelial atypia in EAI.22