Erythema ab igne

A 77‐year‐old woman presented with a 5‐month history of an asymptomatic rash affecting her lower abdomen and proximal thighs. She reported daily use of a hot water bottle to the areas. Examination demonstrated reticulate hyperpigmentation with atrophic foci. Her presentation was classical for erythema ab igne.

Erythema ab igne is characterised by a net‐like pattern of erythema, hyperpigmentation or atrophy in response to chronic infrared radiation.1,2 Repeated exposure to low grade heat (insufficient to cause a thermal burn) is thought to result in the reticulation corresponding to dermal vasodilation and haemosiderin deposition, but its aetiology is poorly understood.1 Differential diagnoses of reticulate eruptions include medium vessel vasculitis, vasculopathies and hypercoagulable states, reticular mucinosis, and prurigo pigmentosa. Management centres on removal of the offending heat source.1 The underlying reason for the patient’s chronic heat exposure (eg, pain) must also be elicited and managed appropriately. Depending on severity, the cutaneous changes may resolve with removal of the heat source. Where dyschromia persists, topical retinoids, 5‐fluorouracil, or laser‐based modalities may offer improvement.1,2 Erythema ab igne is associated with an increased risk of cutaneous malignancy such as squamous cell carcinoma, with a latent period which may extend beyond 30 years.1