Erythema ab Igne on the Thighs of a 53-Year-Old Man

A brownish red, reticulate rash had persisted on the thighs of a 53-year-old man for about 15 years. For the past 20 years, he had applied-daily and for extended periods-a hot water bottle on his legs for soreness following exercise.

Benjamin Barankin, MD, of Edmonton, Alberta, diagnosed erythema ab igne, an uncommon condition in which reticulate, reddish brown patches develop on skin that is repeatedly exposed to an external heat source for prolonged periods. This exposure results in cutaneous hyperthermia and histopathologic changes similar to those seen in sun-damaged skin. Telangiectasia and hyperpigmentation also may develop.

Erythema ab igne is a clinical diagnosis, although a punch biopsy is beneficial in uncertain cases. The condition is usually asymptomatic; however, patients may complain of mild pruritus and burning. The history reveals the use of external heat sources to either keep warm or treat pain. Various heat sources have been implicated, including fireplaces and wood stoves, hot water bottles, heating pads, and heated recliners used to relieve malignancy-related pain or chronic back pain.

In most patients, cessation of heat exposure results in a gradual resolution of the condition over many months. For persistent hyperpigmented lesions, treatment with an Nd:YAG, ruby, or alexandrite laser may improve their appearance. This patient did not want treatment, because he preferred to continue using hot water bottles for his sore legs.