Abstract

Erythema ab igne (EAI) is a rare cutaneous disorder induced by frequent exposure to low-grade heat. Early lesions present as asymptomatic reticulated erythematous macules that typically progress to either hyperpigmented or hypopigmented areas with hyperkeratosis. Keratosis lichenoides chronica (KLC) is a rare dermatosis with unclear pathogenesis, characterized by linear or reticular hyperkeratotic violaceous papules and plaques. It is not clear if it represents a variant of lichen planus or a unique entity. Herein, we present a 92-year-old male patient with a past medical history of colon cancer status post hemicolectomy, prostate cancer status post prostatectomy, and abdominal aortic aneurysm status post repair, who presented to a dermatology clinic with a non-itchy rash with discoloration on the left lateral leg for two months. The patient reported sitting next to a space heater for 15 minutes per day. Clinical examination showed reticulated and hyperpigmented violaceous plaques with healing subcutaneous nodules. A 3 mm punch skin biopsy demonstrated an acanthotic epidermis with hyperkeratosis and hypergranulosis. Atypical keratinocytes, squamous dysmaturation, and dyskeratosis are noted in epidermis, in addition to lichenoid interface dermatitis with underlying dermal elastosis, pigment incontinence, and telangiectasis. The combination of the clinical and pathological features was consistent with erythema ab igne with keratosis lichenoid chronica-like features. In conclusion, EAI may histomorphologically overlap with KLC. A history of chronic heat exposure combined with the characteristic clinical distribution pattern favors EAI. This phenomenon has rarely been reported. To our knowledge, only three similar cases have been described in the literature.

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