A 12-year-old boy with bilateral reticulated hyperpigmentation of the thighs.

Abstract

A 12-year-old otherwise healthy boy presented to the emergency department with a 1-week history of a bilateral anterior thigh “rash” in the middle of a New England winter. As a result of the COVID-19 pandemic, he was attending school remotely. During school hours, in the 3 months leading up to his presentation, he had frequently been sitting with a heating pad on his lap. He denied pruritus, pain, vesiculation, or constitutional symptoms associated with the hyperpigmentation. Medical and family history were unremarkable. On examination, isolated to the bilateral anterior thighs, there were symmetric reticulated hyperpigmented patches (Figure 1). The patient followed up 3 weeks later with mild lightening of the hyperpigmentation (Figure 2). Erythema ab igne (EAI), also known as “toasted skin syndrome,” is characterized as a reticular hyperpigmented dermatosis. Latin for “redness on fire,” the reticulated erythema associated with this condition has been predominantly characterized in light-skinned individuals.1 This case demonstrates EAI in a skin-of-color pediatric patient in an effort to enable recognition of this unique cutaneous pattern that is not as well-documented in darker skin tones. EAI was historically reported as the result of prolonged exposure to wood-burning stoves or open fires; however, with the advent of central heating, it has more recently been linked to the heat emitted by laptops, heating pads, electric blankets, and even heated microwave popcorn.1, 2 The pathophysiology of EAI has yet to be elucidated; however, common heat sources like those aforementioned emit low levels of infrared radiation that likely affect the elastic tissue in the dermal venous plexus.3 Clinically, in lighter-skinned individuals, this presents as a reticulated erythematous patch at the location of the heat source matching the distribution of the venous plexus. The erythematous network is initially blanchable, but with repeated heat exposure it transforms into a non-blanchable, static hyperpigmented patch. In the skin-of-color patients, the erythematous stage of EAI is much harder to appreciate but follows a similar course of progressing to a hyperpigmented static patch.4 Bullae and keratotic features can also occasionally be seen.3 These patches are typically asymptomatic, but some patients may report a mild burning sensation or pruritus.5 The differential diagnosis for reticulated hyperpigmentation in a child includes livedo reticularis, cutis marmorata, livedoid vasculopathy, and cutis marmorata telangiectatica congenita (CMTC). Livedo reticularis and cutis marmorata are both transient, rarely result in static hyperpigmentation, and are typically associated with exposure to the cold rather than heat. Livedoid vasculopathy presents with retiform purpura or ulcerations and is painful, as opposed to the asymptomatic nature of EAI. Finally, CMTC presents at birth and may exhibit atrophy and ulcerations at the site of the reticulated hyperpigmentation making this unlikely in our pre-teen boy.3 EAI is a clinical diagnosis, although early patches are histologically characterized by epidermal atrophy, vasodilation of superficial papillary dermal blood vessels, and dermal deposition of melanin and hemosiderin.6 As the patches progress, degeneration of elastic tissue in the dermis, hyperkeratosis, epithelial atypia with dyskeratosis, and occasionally an interface dermatitis can be seen.6, 7 EAI may histologically mimic actinic keratoses suggesting that heat, like ultraviolet light, may induce clonal mutations in epithelial cells.7 Notably, there have been reports of patients developing squamous cell carcinoma and rare cases of Merkel cell carcinoma and marginal zone B-cell lymphoma within existing EAI patches up to 30 years after their primary presentation.7-9 Thus, regular follow-up until patch resolution and education surrounding the long-term potential for malignancy is recommended. Treatment primarily revolves around discontinuing exposure to the offending heat source, which usually results in the resolution of early EAI patches. Similar to the treatment of actinic keratoses, chronic cases have been successfully treated with topical 5-fluorouracil.4 A recent case also reported resolution with oral mesoglycan and topical bioflavonoids.10 Additional hyperpigmentation interventions considered for our skin-of-color patient included tranexamic acid, hydroquinone, and the Q-switched or picosecond Nd-YAG laser. EAI is normally rarely seen in clinical practice; however, the diagnosis may be on the rise. The repercussions of the COVID-19 pandemic have forced children to attend school remotely resulting in prolonged exposures to laptops or other home heat sources. Therefore, clinicians should be increasingly aware of EAI and its nuanced presentation in pediatric skin-of-color patients. Specifically, EAI may present with either subtle or no appreciable erythema (ie, sine erythema), yet it must be considered in the differential diagnosis for a reticulated hyperpigmented patch in a skin-of-color individual.