A 47-year-old woman with chronic low back pain presents with a chief complaint of a persistent rash along her posterior trunk. The discoloration has slowly progressed over the last year and does not fluctuate in response to hot or cold temperatures. She has no history of vasospastic disease. On examination an irregular reticular fixed brownish discoloration overlies her entire back. She admits to sleeping on a heating pad for the last 3 years due to her unremitting back pain. A diagnosis of erythema ab igne (EAI) or “toasted skin syndrome” is rendered (Figure 90-1).
Due to infrequency of EAI, limited epidemiologic data exists.
Although previously a disorder associated with protracted exposure to stoves and open fires, the majority of cases are now linked to laptops and heating pads or blankets.
Slight female predominance but no overt racial predilection.
While EIA was formerly primarily identified in middle-aged subjects, in a recent review, affected women averaged 25 years and men averaged 20 years of age.1
ETIOLOGY AND PATHOPHYSIOLOGY
Table 90-1 lists various causes of EAI.
Occupations at risk include cooks, bakers, foundry workers, silversmiths, and glass blowers.
Patients with chronic pain are at risk due to heating pad or hot water bottle application to various body sites.
Modern day cases are increasingly linked to laptop use on the thighs.
EIA results from prolonged and repeated exposure to thermal radiation. The heat exposure is not intense enough to burn the skin, yet it is severe enough to evoke injury and subsequent discoloration.
Causative temperatures typically range from 43 to 47°C (109-117°F)
The definitive pathomechanism that leads to EIA is unclear, yet appears to involve heat injury to the epidermis and superficial vascular plexus that ultimately leads to dilation and hemosiderin deposition in a reticulate pattern.2
The length of recurrent thermal exposure required to elicit EIA typically ranges from months to several years. Rarely, the discoloration has been reported as early as 1 to 2 weeks after contact with a heat source. The exposure risk is cumulative.