Erythema Ab Igne and Malignant Transformation to Squamous Cell Carcinoma.

Erythema ab igne (EAI) is a cutaneous reaction resulting from prolonged exposure to an infrared heat source at temperatures insufficient to cause a burn. It is most commonly reported on the lower extremities and back, and it presents with persistent areas of reticular erythema associated with hyperpigmentation, epidermal atrophy, and telangiectases. Erythema ab igne traditionally is associated with chronic exposure to open fires and coal stoves. More recently, other implicated causes include heating pads, laptop computers, heated furniture, and electric space heaters. Histologic features of squamous atypia with basal layer crowding and loss of maturation throughout the epidermis can be seen in later stages of EAI. Therefore, although EAI is predominantly a chronic pigmentary disorder, a percentage of patients might be at increased risk for cutaneous malignant transformation, including squamous cell carcinoma (SCC).