Laboratory Studies
Laboratory findings may be abnormal if the erythema ab igne is associated with a systemic disease.
Procedures
Perform a 3- or 4-mm punch biopsy if the diagnosis of erythema ab igne is uncertain.
Histologic Findings
Microscopic changes in erythema ab igne depend on the type of heat, the length of exposure, and the area of the body involved. [19]
Epidermis
Histologically, erythema ab igne is similar to actinic keratoses, with the epidermis showing squamous atypia. [19] Early erythema ab igne shows atrophy of the malpighian layer and increased epidermal and upper dermal melanin with dermal vasodilatation. [34] Advanced cases show epidermal vacuolation, focal hyperkeratosis, and dyskeratosis. [34] Epidermal dysplasia within abnormal elastic tissue may also be seen. [34] In early erythema ab igne lesions, epidermal atrophy with loss of the rete ridges is seen. Some patients show focal or confluent hyperkeratosis, dyskeratosis, keratinocyte atypia, and, occasionally, melanocyte atypia. [40] Hyperpigmentation, with focal degenerative changes of basal keratinocytes, is seen. [40] Similar alterations can be observed in chronic actinic skin damage. [40]
Dermis
Melanin incontinence occurs with melanophages present in the upper dermis. [40] Collagen degeneration and a relative increase in dermal elastic tissue are seen. In contrast to solar elastosis, this is not basophilic on hematoxylin and eosin–stained specimens. [40] Telangiectasis within the papillary dermis and occasional hemosiderin may be seen more commonly on the legs in patients with erythema ab igne. [40] An apparent functional activation of melanocytes with numerical increase of dendritic processes is also observed. [40] Abundant melanophages and occasional elastic fiber alterations as seen, similar to actinic elastosis. No alterations consistent with preneoplastic skin conditions are observed. [40]
Increased elastosis with fragmented collagen fibers are seen. [34] Minimal basophilia and homogenization of elastic fibers, which are prominent in solar elastosis, are seen in erythema ab igne. [34] Both melanophages and hemosiderin are seen in the dermis. [34] Varying degrees of dermal lymphohistiocytic infiltration are present. [34] Extravasation of red blood cells in inconsistent. [34] Accumulation of dermal elastic tissue can be seen, which is an early sign of both UV radiation- and heat-induced skin damage. [19]
Other considerations
Squamous cell carcinoma and Merkel cell carcinoma may arise in the lesions of erythema ab igne on rare occasions. [19] The most common thermally induced cancer, squamous cell carcinoma, tends to occur after a long latent period of more than 30 years. [19] Squamous cell carcinoma in burn scars often begins as a chronic ulcer, which slowly enlarges and tends not to heal. Although these carcinomas tend to be of low-to-intermediate grade histologically, they may also be aggressive, with metastases and a poor prognosis reported in greater than 30% of cases. [19] Merkel cell carcinoma is an aggressive neoplasm, characterized by local recurrence in approximately 30% of cases and up to 30% mortality. [19]
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Red rash resembling lacework or a fishing net on leg.
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Red rash resembling lacework or a fishing net on back.
