Does the Rash on This Boy’s Thighs Look Familiar?

Case: An 11-year-old boy is referred for evaluation of an asymptomatic rash on his anterior thighs. The macular, partially blanching, erythematous to slightly tan, reticulated rash began 2 months earlier and involved the left thigh more than the right.

The child has had no medical illnesses and is not taking any medications. He is an active and social child, although much of his socializing he admits is done on his laptop, which he uses every day sometimes for several hours at a time.

Does the rash on this boy’s thighs look familiar?

(Answer on next page.)

The pattern of the rash and history are consistent with erythema ab igne from use of a laptop propped on the thighs.

Many cases of erythema ab igne associated with frequent laptop use or “laptop thigh” have been reported since the condition first appeared in the literature in 2004.¹ It is common in young adults aged 26 years and younger, probably because of more time-concentrated use of laptops for study and socialization.² As availability and use of laptops increases in the pediatric population, we expect to see more children presenting with erythema ab igne of the thighs.

Erythema ab igne is a cutaneous change secondary to thermal radiation insufficient to result in a burn. The first clinical change of erythema ab igne is mottling, a blanchable reticular erythema, followed by fixed pigmentary changes if the thermal insult persists.

Histologically, early erythema ab igne is characterized by an atrophic change of the epidermis, vasodilatation of cutaneous vessels and deposition of pigment, both melanin and hemosiderin, in the dermis. With chronic heat exposure, these skin changes progress to more marked epidermal atrophy with flattening of the rete ridges along with dyskeratosis and squamous atypia. There may be an increased risk of squamous cell carcinoma or Merkel cell carcinoma with long-term heat exposure.³

Common exposures that predispose to development of erythema ab igne include habitual use of heating pads on the back and laptops placed directly on the thighs. The unilateral predominance of the rash in this child corresponds with the optical drives, which are typically located on the left side of laptops. Other laptop heat sources include the battery and exhaust system, especially if heat cannot be dissipated secondary to occlusion by the skin of the thighs. Laptops are known to reach temperatures up to 44°C, which is sufficient to cause this rash.⁴

Management includes removal of the heat source. The rash fades over time, although long-term exposure may result in permanent pigmentation.⁵