A 26 year old girl presented with diffuse reticulate erythematous to brown, macular, non-blanching discoloration around her umbilicus. No evidence of telangiectasia, atrophy, bullae, or superficial erosions was seen. It was asymptomatic and she often applied hot water bags to her abdomen for recurrent abdominal pain. What is the likely diagnosis?

Erythema ab igne (EAI) is characterized as localized areas of reticulated erythema and hyperpigmentation due to chronic and repeated exposure to infrared radiation. Patients with erythema ab igne have a history of repeated exposures to heat at a lower level than that which causes a thermal burn. The exposure, which need not be of long duration, results in cutaneous hypehermia in the range of 43-47degC. No definitive therapy is available for erythema ab igne. Reducing or eliminating exposure to the heat source early in the erythema ab igne disease process may reverse the hyperpigmentation. In cases of sho duration, complete resolution occurs with removal of the offending heating device. More advanced cases may respond somewhat to tretinoin, and 5-fluorouracil cream can help clear epithelial atypia. It has been described in the setting of internal inflammation (chronic low back pain, pancreatitis, peptic ulcer disease) and primary or metastatic cancer (rectal cancer, pancreatic carcinoma, myeloma). Malignant transformation may ensue if the diagnosis is missed and exposure to the heat source is not discontinued. Ref: Dvoretzky I, Silverman NR. Reticular erythema of the lower back. Erythema ab igne. Arch Dermatol. Mar 1991;127(3):405-6, 408-9; Meffe JL, Davis BM. Furniture-induced erythema ab igne. J Am Acad Dermatol. 2000;34:516-517; A reticulated eruption: BMJ 2012;344:e359.