Julie Man, MD,¹ Joseph M. Lam, MD, FRCPC,²

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Abstract: A 13-year-old girl presented with a 3-month history of a reticulate hyperpigmented patch over the lower abdomen. Her past medical history was significant for recurrent abdominal pain, Ehlers-Danlos syndrome, a mild learning disability, and multiple allergies. On physical examination, she had a reticulate, hyperpigmented patch distributed diffusely over the lower abdomen (Figure 1). The remainder of her exam was unremarkable. Upon questioning, it was revealed that the patient had been applying a hot water bottle to the lower abdomen for the last 4 months to help relieve the discomfort associated with the abdominal pain. This history led to the diagnosis.

Key Words: Erythema ab igne, hyperpigmentation, reticulate, thermal injury.

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Erythema ab igne may present as a transient erythematous eruption, or as a reticulate hyperpigmentation.

Erythema ab igne is a clinical diagnosis which rarely requires biopsy confirmation.

Direct questioning about heat sources, such as prolonged laptop computer use, aids the diagnosis.

Treatment consists of patient education and removal of the heat source.

1. Erythema ab igne is a recognizable condition associated with chronic exposure to heat sources such as heating pads, hot water bottles, electric blankets, space heaters and laptop computers.

2. The differential diagnosis for erythema ab igne includes livedo reticularis, livedoid vasculitis, cutis marmorata telangiectatica congenita, a reticulate port-wine stain and poikiloderma.

3. The most important treatment for erythema ab igne is recognition and removal of the source of infrared radiation.

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Francesca Cheung, MD CCFP, is a family physician with a special interest in dermatology. She received the Diploma in Practical Dermatology from the Department of Dermatology at Cardiff University in Wales, UK. She is practising at the Lynde Centre for Dermatology in Markham, Ontario and works closely with Dr. Charles Lynde, MD FRCPC, an experienced dermatologist. In addition to providing direct patient care, she acts as a sub-investigator in multiple clinical studies involving psoriasis, onychomycosis, and acne.

Abstract
Erythema ab igne (EAI) is a localized hypermelanosis with erythema in a reticulated pattern. It is triggered from repeated exposure to heat and infrared radiation. Actinic keratosis, squamous cell carcinoma, and Merkel cell carcinoma have been reported in patients after chronic exposure to infrared radiation. EAI is diagnosed based on clinical symptoms. If the diagnosis is uncertain, a skin biopsy may be performed. Early in the disease process, elimination of the heat source may lead to complete resolution of the symptoms.