Huynh N, Sarma D, Huerter C Omaha

F 53 - Discolored skin over right thigh extending down to the calf for “many months.” - No exposure to heating ducts or fire place exposure at home or work. - Long term use of electric blanket with direct contact on the affected skin.

Reticular, erythematous, and hyperpigmented patches on the right distal extremity.

Skin biosy shows epidermal atrophy and upper dermal perivascular chronic inflammation

Higher magnification shows dyskeratotic keratinocyte in the epidermis, mild papillary melanosis and superficial perivascular chronic inflammation

Elastic stain shows increased elastic tissue especially in the mid-dermis

 Erythema ab igne (EAI) is a rare condition characterized by reticular, erythematous, and hyperpigmented patches which may result from chronic exposure to external heat sources.  Before the advent of central heating EAI was once considered a common condition most often found on the distal extremities of individuals who stood or sat close to burning stoves or open fires.  Cases of EAI have been identified with repeated application of hot-water bottles or heating pads, in the treatment of chronic pain, such as backache.  Certain occupations that chronically expose workers to external heat sources such as silversmiths, jewelers, bakers, foundry workers, and kitchen workers have also given rise to cases of EAI.

 EAI has also been reported in individuals using electric space heaters, car heaters,heated recliners,heating/cooling blankets, heated popcorn kernels, hot bricks, infrared lamps, wood stoves, coal stoves, electric stove/heater, peat fires, steam radiators, and most recently laptop computers as users place computers on their propped legs.

 The pathogenesis of EAI is not yet understood.  It is suggested that chronic heat exposure denatures DNA in squamous cells in conjunction with ultraviolet radiation.  A single episode of heat exposure is insufficient to induce burn or skin manifestation associated with EAI.  Chronic heat exposure is needed to accumulate the damages; generating first a pattern of erythema which then progresses to a reticular hypo- and hyperpigmentation.  Although infrequent, subepidermal bullae and diffuse hyperkeratosis may occur.  In severe cases, poikiloderma, thermal keratosis, ulceration and secondary skin malignancy, such as squamous cell carcinoma in situ, squamous cell carcinoma, and neuroendocrine carcinoma, (Merkel cell carcinoma), may result although it is quite rare.

 Histologic features of EAI are nonspecific.  In the early stages, EAI may appear normal on hematoxylin and eosin stains.  It may reveal epidermal atrophy, rete effacement, basal vacuolar changes, and pigmentary incontinence.  The dermis may be infiltrated by lymphocytes, melanophages, histiocytes, and neutrophils with postcapillary venules’ dilation and congestion.  Perhaps the most distinguishing feature of EAI is the increased elastic tissue in the upper and mid dermis and the presence of squamous cell atypia which resembles actinic keratoses.  Hyaluronic acid and iron deposition have also been described.

 EAI is more common in overweight women.  Patients may be asymptomatic or may present with mild sensation of burning or pruritus.  The differential diagnosis includes solar elastosis, erythema dyschromicum perstans, acanthosis nigricans, actinic keratoses, livedo reticularis, livedoid vasculitis, poikiloderma atrophicans vasculare, and cutaneous reactive angiomatoses.  EAI has an excellent prognosis.  Treatment of EAI is immediate removal of heat sources.  5-fluorouracil cream has shown to be effective in eliminating atypical squamous cells in EAI.  In severe cases where pigmentation persists, tretinoin or hydroquinone could be used topically.  Biopsy is needed if there are suggestions of malignancy such as unrelenting ulcer with heaved up borders, or nodules.

REFERENCE: Huynh N, Sarma D, Huerter C.(2011). Erythema ab igne: a case report and review of the literature Cutis 88:290-92, PUBMED.