Clinical Image: Erythema ab igne: a mimicker of rheumatoid vasculitis

The patient, a 34‐year‐old woman, presented with a 2‐month history of livedo reticularis lesions on her lower extremities. Three years previously, she was diagnosed with seropositive rheumatoid arthritis, and her arthritis was in remission with a disease‐modifying antirheumatic drug. She did not have fever, numbness, or other subjective symptoms. Her anti‐nuclear antibodies were positive in a low titer, but she had negative results for anti–double‐stranded DNA antibodies, anti‐phospholipid antibodies, and anti‐neutrophil cytoplasmic antibodies. Her serum complement levels remained within normal ranges. On further probing about the history of her present illness, she reported using an electric heater during the winter. A clinical diagnosis of erythema ab igne (EAI) was made. EAI is a pathognomonic cutaneous reaction caused by chronic heat exposure below the threshold for thermal burn (1). A biopsy is not necessary for EAI diagnosis. Because this is a clinical diagnosis, a thorough medical history and physical examination are essential. In this case, rheumatoid vasculitis was a differential diagnosis. The prognosis for EAI is good once the offending source is removed (2). The patient's livedo reticularis completely disappeared after she stopped using the heater in the spring. Written informed consent for publication of this clinical image was obtained from the patient.

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