CASE
A 45-year-old woman presented for evaluation of a rash that was more or less unchanged for the past 8 to 10 years. The rash was asymptomatic for the most part, except for occasional “spells” during which the surface of the rash became a bit scaly and the rash became mildly pruritic. It had persisted despite a number of treatments, including topical and oral antifungals and the application of numerous topical corticosteroid creams. In all that time, she had never been examined by a dermatology clinician and had never had a biopsy.
The patient denied having any other skin problems but stated that she had other health issues. Rheumatoid arthritis, lupus, and fibromyalgia had been diagnosed in our patient. She was taking hydroxychloroquine (Plaquenil) and various OTC NSAIDs for these conditions.
When asked in particular about the skin problem on her back, she admitted to using a large heating pad turned up “as high as it will go” for her back pain. On some days, she used the pad all day, and she left it on her back most nights.
Examination revealed an impressively large, reticular (netlike) macular pattern of hyperpigmentation that covered most of the patient's back (Figure 1). It was nonblanchable, and a bit of scaling was better felt than seen in a few focal areas. Potassium hydroxide test (KOH prep) was negative for fungal elements.
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DISCUSSION
The correct diagnosis is erythema ab igne (EAI). Literally translated, the term means redness from fire. EAI is a reaction of the skin and underlying vasculature to chronic exposure to moderate external heat sources that eventuates in a permanent reticular pattern of surface hyperpigmentation. Eventually, other changes, such as telangiectasias and atypia of epidermal cells occur. These changes, over time, are similar to those seen with chronic UV damage and can even lead to the apparently related development of precancerous and cancerous foci.
Poikiloderma vasculare atrophicans (PVA) usually represents a manifestation of the patch stage of cutaneous T-cell lymphoma; although PVA also manifests with dermatomyositis or radiation dermatitis. Tinea versicolor does not typically demonstrate a reticular pattern; instead, hyper- or hypopigmented macules with annular borders are seen. KOH prep is likely to have shown the short hyphal elements and spores of the causative commensal yeast, Malassezia furfur. Livedo reticularis (LR) is usually transient, as opposed to the fixed nature of our patient's condition, but did bear consideration as a real diagnostic possibility. See below for more discussion of the differential. Our patient's strong history of daily and prolonged use of the heating pad obviated the necessity to rule out PVA and LR with biopsy.
Comment An increase in cases of EAI has been reported in women who rest laptop computers on their legs for hours. The condition has also been diagnosed in cooks, people who run the car heater on high during long daily commutes, and factory workers who sit all day with a heating pad across their lap to keep warm in a cold work environment.
EAI was first seen on the legs of women who habitually sat in front of the fireplace all day in an effort to stay warm. EAI was considered a sign of possible hypothyroidism or anemia, a connection still worth considering today.
Other than halting the offending activity, the only treatment for EAI is laser. A mild case may eventually resolve on its own if the direct exposure to heat is discontinued. JAAPA
Joe Monroe practices at the Dawkins Dermatology Clinic, Oklahoma City, and is the department editor for Dermatology Digest. He has indicated no relationships to disclose relating to the content of this article.