Diagnosis: Erythema ab igne
Erythema ab igne is characterized by localized erythema, reticulosis, and hypo-/hyperpigmentation, with telangiectsia and skin atrophy appearing in severe cases. This condition is caused by continuous exposure to sources of heat for prolonged periods of time.1 Patients often do not connect their heat exposure to the rash, so you must recognize the local pattern of erythema ab igne and use your detective skills to identify the source.
History: Old disease, modern causes
Erythema ab igne has been noted for many years, and the sources of heat have changed over time. It used to be seen in women who stayed for long periods in front of open fires or furnaces to cook.2,3 Most of the lesions appeared on the medial side of the thigh and the lower leg.
In modern times it is seen on different parts of the body depending on the heat source that initiated the pathology, the angle of the heat radiation, the morphology of the skin, and the layers of clothing.1 Some of the modern causes of erythema ab igne are repeated application of hot water bottles or heat pads to treat chronic pain, exposure to car heaters and furniture with internal heaters, use of a laptop computer for long periods,4 and cook stoves, for restaurant workers who stand for long periods near the heat.3 Ultrasound physiotherapy was also reported as a cause.5 Recently, a case caused by frequent and prolonged hot bathing was reported.6
Clinical features: Mottled pattern clinically, subtle changes
The pattern of lesions form as a result of multiple exposures to the source of heat. Skin lesions may not appear immediately after the exposure—it might take a month to show up.7 Changes start as a reddish-brown pigmentation distributed as a mottled rash, followed by skin atrophy. Telangiectasias with diffuse hyperpigmentation and subepidermal bullae may also develop.8 Some patients complain of mild pruritus or burning sensation, but most patients are asymptomatic.9 Erythema ab igne should be differentiated from other diseases with skin changes that mimic its presentation (TABLE).
If clinically warranted, perform a biopsy to exclude the possibility of malignant formation. Histopathology results show epidermal atrophy, subepidermal separation, and haziness of the dermoepidermal junction. Dilatation of capillaries and connective tissue disintegration, elastosis, hemosiderin deposition, melanocytosis, and abundance of inflammatory cells are all seen in the dermis.10 Some of these lesions might progress to actinic keratosis, which could be a precursor for squamous cell carcinoma of the skin.11 In some rare cases, Merkel cell carcinoma has developed in areas of erythema ab igne.12