Mottled rash on the dorsal feet of an adolescent girl

An 18-year-old girl from a semi-urban area sought remote consultation through teledermatology for a “winter season” rash on her feet. On examination, distinct mottled hyperpigmentation in a reticulate, mesh-like pattern on the dorsal aspect of both feet, with the left side showing more prominence, was observed [Figures 1 and 2]. Further, probing revealed that she had been spending prolonged hours studying next to a heater with the bare left foot positioned directly next to the appliance. A diagnosis of “Erythema ab igne” was established, and she was counseled to avoid the proximity of the bare area to the heat source.

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Figure 1:

Mottled, reticulate hyperpigmentation on dorsum of left foot; (placed directly next to heat source).

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Figure 2:

Similar, faint rash on dorsal aspect of right foot; (placed relatively further from heat source).

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Erythema ab igne or “toasted skin syndrome” results from repeated and prolonged exposure to low levels of infrared radiation, such as from a heating appliance, insufficient to cause a burn. This exposure causes degeneration of elastic fibers and basal cells leading to the release of melanin and dark lacy discoloration.^[1] The rash initially manifests as transient, mottled erythema and progresses to fixed, reticulate hyperpigmentation.^[2] The condition, less common in youth, may be misdiagnosed as livedo reticularis leading to unnecessary immunological investigations, but may be distinguished by its pigmentary rather than telangiectatic changes.^[1]