What is erythema ab igne

Erythema ab igne also known as toasted skin syndrome, is a skin condition that occurs after repeated exposure to heat at temperatures lower than those that cause noticeable burns on the skin. Erythema ab igne was once a common condition seen in the elderly who stood or sat closely to open fires or electric space heaters. Although the introduction of central heating has reduced erythema ab igne of this type, it is still found in individuals exposed to heat from other sources.

Limited exposure to heat, insufficient to cause a direct burn, causes a mild and transient red rash resembling lacework or a fishing net. Prolonged and repeated exposure causes a marked redness and coloring of the skin (hyper- or hypo-pigmentation). The skin and underlying tissue may start to thin (atrophy) and rarely sores may develop. Some patients may complain of mild itchiness and a burning sensation.

Erythema ab igne is associated with the following:

• Slight increase in malignancy when the cause is due to a hydrocarbon heat source
• Actinic keratosis and squamous cell carcinomas in a number of cases after a long latent period: These include cases from the chronic heat of a sunken hearth (irori) and underfloor braziers covered with a quilt (kotatsu) ¹
• Heated brick beds in northern China (kang cancers) ¹
• Coal-burning baskets in Kashmir in India (kangri cancers) ¹
• Peat fire cancers in Ireland
• Benzene-burning pots in Japan (kairo cancers) ¹

Although rare, skin cancers have been known to arise from areas of erythema ab igne, usually from longstanding lesions, twenty or even thirty years later. The majority of these are squamous cell carcinomas, although other types of skin cancers have also been reported. In general, the risk of skin cancer arising from erythema ab igne, while higher than that of unaffected skin, is very low.

There is no reliable treatment for the discoloration seen in erythema ab igne. Removing the causative heat source early in the course of the skin changes is the most important step you can take, and it usually results in complete resolution over months. Longstanding lesions from repeated long-term exposure may, however, be permanent. In some cases, the lesions improve with topical agents such as retinoids or the chemotherapy agent 5-fluorouracil. Some people may respond to treatment with certain types of lasers as well.

Erythema ab igne causes

It is not really known how or why the skin discoloration seen in erythema ab igne occurs. Causes of erythema ab igne include open fires, space heaters, radiators, heating pads used for chronic pain, and electric blankets. There have been increasing recent reports of erythema ab igne associated with the use of laptop computers directly on the lap.

Typically, erythema ab igne affects the legs of women aged 40-70 years who use indoor fire as a heat source. Erythema ab igne reportedly affects the face and/or palms of cooks who work over an open fire.

Some patients use a heat source (eg, heating pad, hot water bottle, heated recliner, heated blanket) to relieve chronic pain ². In these patients, determine the etiology of the pain. In the case of heating pads and/or hot water bottles, erythema ab igne can occur in patients with pain associated with either primary or metastatic malignancy, as well as with pain associated with chronic pancreatitis ³. Heated recliners (reclining chairs) have been reported to cause erythema ab igne in patients with chronic lower back pain ⁴. The application of heated popcorn kernels applied to the skin to reduce arthritic pain caused erythema ab igne in one patient ⁵. One case report describes erythema ab igne in a patient with diabetic neuropathy ⁶.

Other heat sources may be involved. Erythema ab igne has been described subsequent to sauna belt usage for abdominal obesity ⁷. A car heater reportedly caused erythema ab igne in one patient ⁸. More recently, using laptop computers while they are propped on the legs has resulted in the development of erythema ab igne. Some laptop computers can generate significant heat that can result in erythema ab igne when placed on the lap for prolonged periods ⁹.

The following is a summary of heat sources reported to cause erythema ab igne ¹⁰:

• Heating pads
• Hot water bottles
• Electric stoves/heater
• Open fires
• Coal stoves
• Peat fires
• Wood stoves
• Steam radiators
• Car heaters
• Heated reclining chairs
• Heating or electric blanket
• Hot bricks
• Infrared lamps
• Microwave popcorn
• Laptop computer
• Automobile seat heater
• Hot bathing

Erythema ab igne symptoms

Erythema ab igne (toasted skin syndrome) starts off appearing as a lacy or net-like (reticulated) discoloration of the skin. This may be a transient pink or red in color initially but eventually becomes a gray or brown discoloration if the heat exposure continues.

Localized lesions seen today reflect the different sources of heat that people may be exposed to. Examples include:

• Repeated application of hot water bottles or heat pads to treat chronic pain, e.g. chronic backache
• Repeated exposure to car heaters or furniture with built-in heaters
• Occupational hazard for silversmiths and jewelers (face exposed to heat), bakers and chefs (arms).

Erythema ab igne complications

Malignant degeneration may occur and should be monitored.

Erythema ab igne diagnosis

A patient history of excessive exposure to heat in the area of onset facilitates clinical diagnosis of erythema ab igne ¹¹. The duration of the repeated exposure necessary to provoke alterations in the skin varies from months to several years, and the damage appears to be cumulative ¹². Commonly, patients with erythema ab igne report mild pruritus and burning.

Your doctor will perform a 3- or 4-mm punch biopsy if the diagnosis of erythema ab igne is uncertain.

Microscopic changes in erythema ab igne depend on the type of heat, the length of exposure, and the area of the body involved ¹³.

Epidermis

Histologically, erythema ab igne is similar to actinic keratoses, with the epidermis showing squamous atypia ¹³. Early erythema ab igne shows atrophy of the malpighian layer and increased epidermal and upper dermal melanin with dermal vasodilatation ¹. Advanced cases show epidermal vacuolation, focal hyperkeratosis, and dyskeratosis ¹. Epidermal dysplasia within abnormal elastic tissue may also be seen ¹. 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 ¹⁴. Hyperpigmentation, with focal degenerative changes of basal keratinocytes, is seen. Similar alterations can be observed in chronic actinic skin damage ¹⁴.

Dermis

Melanin incontinence occurs with melanophages present in the upper dermis ¹⁴. 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 ¹⁴. Telangiectasis within the papillary dermis and occasional hemosiderin may be seen more commonly on the legs in patients with erythema ab igne ¹⁴. An apparent functional activation of melanocytes with numerical increase of dendritic processes is also observed ¹⁴. Abundant melanophages and occasional elastic fiber alterations as seen, similar to actinic elastosis. No alterations consistent with preneoplastic skin conditions are observed ¹⁴.

Increased elastosis with fragmented collagen fibers are seen ¹. Minimal basophilia and homogenization of elastic fibers, which are prominent in solar elastosis, are seen in erythema ab igne ¹. Both melanophages and hemosiderin are seen in the dermis ¹. Varying degrees of dermal lymphohistiocytic infiltration are present ¹. Extravasation of red blood cells in inconsistent ¹. Accumulation of dermal elastic tissue can be seen, which is an early sign of both UV radiation- and heat-induced skin damage ¹³.

Other considerations

Squamous cell carcinoma and Merkel cell carcinoma may arise in the lesions of erythema ab igne on rare occasions ¹³. The most common thermally induced cancer, squamous cell carcinoma, tends to occur after a long latent period of more than 30 years ¹³. 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 ¹³. Merkel cell carcinoma is an aggressive neoplasm, characterized by local recurrence in approximately 30% of cases and up to 30% mortality ¹³.

Erythema ab igne treatment

No definitive therapy is available for erythema ab igne. The source of chronic heat exposure must be avoided. If the area is only mildly affected with slight redness, the condition will resolve by itself over several months. If the condition is severe and the skin pigmented and atrophic, resolution is unlikely. In this case, there is a possibility that squamous cell carcinomas may form. If there is a persistent sore that doesn’t heal or a growing lump within the rash, a skin biopsy should be performed to rule out the possibility of skin cancer. Abnormally pigmented skin may persist for years. Treatment with topical tretinoin and 5-fluorouracil cream ¹⁵ may improve the appearance. In patients with chronic erythema ab igne that results in hyperpigmentation, photothermolysis using the Nd:YAG, ruby, or alexandrite laser may improve the appearance of the lesions of erythema ab igne.

Long-Term Monitoring

As in patients with chronic solar damage, monitor patients with erythema ab igne at regular intervals for possible development of thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma. In addition, although not yet reported, other cutaneous malignancies (eg, malignant melanoma) feasibly may develop within the affected areas.

Erythema ab igne prognosis

Erythema ab igne prognosis is good, except those cases associated with internal disease or metastatic malignancy. Early changes, such as erythema and little or no hyperpigmentation, may resolve within several months. Chronic and repeated exposure to heat may result in permanent changes such as hyperpigmentation and atrophy. In addition, thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma have been reported within the lesions of erythema ab igne.

Mortality/morbidity

Chronic repeated exposure to infrared radiation may result in changes similar to those seen with chronic repeated ultraviolet radiation. Carcinoma can develop from dysplastic keratinocytes harbored within the reticulated hyperpigmentation. Thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma have been reported in patients after chronic exposure to infrared radiation ¹⁶. In one 90-year-old woman with erythema ab igne, Merkel cell carcinoma developed adjacent to squamous cell carcinoma. Occasionally, the first sign of splenomegaly, pancreatitis, pancreatic cancer, and other cancers is erythema ab igne resulting when patients apply external heat to relieve the underlying pain ¹⁵.

Work exposure to heat (eg, for bakers, silversmiths, and boiler operators) may cause erythema ab igne ¹⁴. Additionally, erythema ab igne has been reported to appear on the legs following prolonged, daily exposure to a car heater.

References

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14. Dvoretzky I, Silverman NR. Reticular erythema of the lower back. Erythema ab igne. Arch Dermatol. 1991 Mar. 127(3):405-6, 408-9.
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16. Arrington JH 3rd, Lockman DS. Thermal keratoses and squamous cell carcinoma in situ associated with erythema ab igne. Arch Dermatol. 1979 Oct. 115(10):1226-8.