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Am Fam Physician. 2006;74(10):1765-1766

Author disclosure: Nothing to disclose.

A 19-year-old woman presented with a rash on her back (see accompanying figure). She denied experiencing pain, itching, joint aches, malaise, or photosensitivity. The patient had no personal or family history of connective tissue disease. Physical examination revealed reticulated erythema on her lower back. There was no evidence of periungual telangiectases or malar erythema. The patient admitted to sleeping on a heating pad because of a back injury in the weeks before her visit.

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Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?


The answer is C: erythema ab igne. Erythema ab igne represents a skin reaction to thermal injury.1 Typically, the affected area has a net-like pattern of blue-gray discoloration, sometimes with associated erythema and scale. Patients often complain of burning or pruritus of the involved area. The mainstay of treatment is avoidance of the heat source. Chronic heating pad use and warming in front of a wood-burning stove are common causes of erythema ab igne. Use of a laptop computer is a more modern source of this disorder.2 The discoloration slowly resolves over months to years; however, permanent scarring and hyperpigmentation can occur.

Discoid lupus erythematosus is a chronic inflammatory disease consisting of fixed, atrophic, erythematous papules and plaques that often are distributed on the head and neck.3 Pigmentary changes, hyperpigmentation and hypopigmentation, may be associated with discoid lupus erythematosus, as is extensive scarring. Epidermal changes include dilated (patulous) pores, prominent scale, and keratotic follicular plugging.

The lesions of systemic cutaneous lupus erythematosus consist of scaly, superficial, inflammatory macules, patches, and plaques that are classically photodistributed.3 Lesions of systemic cutaneous lupus erythematosus are annular or psoriasiform.

Erythema chronicum migrans typically is associated with Lyme disease caused by Borrelia burgdorferi.4 Approximately three fourths of patients with Lyme disease will develop erythema chronicum migrans.4 This starts as a small erythematous patch at the site of the bite and progresses to an annular erythema that may be 20 cm or more in diameter.

Livedo reticularis is a condition caused by dilation of capillary blood vessels and stagnation of blood within these vessels. Subsequently, a mottled discoloration of the skin occurs. It is described as a reticular, reddish blue, cutaneous discoloration surrounding a pale central area.5 This may be a marker of systemic conditions such as arterial embolic disease.

Discoid lupus erythematosusHyperpigmented patches or plaques, often with hypopigmented areas; typically involves sun-exposed areas
Systemic cutaneous lupus erythematosusErythematous papulosquamous patches on photo distributed areas mainly on upper body
Erythema ab igneMottled and reticulated nonblanching erythematous patches; usually in localized area corresponding to exposure to a nonburning heat source
Erythema chronicum migransErythematous patch with expanding annular erythema; possible history of tick bite
Livedo reticularisReticulated erythema on extremities with red and blue coloration

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This series is coordinated by John E. Delzell Jr., MD, MSPH, associate medical editor.

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