The condition caused by an over exposure to radiant heat or infrared radiation is called Erythema ab igne or hot water bottle rash. In medical terms it is the constant exposure to heat on the skin over a long period of time which causes a thermal burn and can also be termed as ephelis ignealis, erythema a calore, and ephelis ab igne. It is marked with reticulated redness and coloring of the skin, associated with itching and burning sensation.
This Erythema ab igne syndrome affects bakers, silversmiths, boiler operators as they are daily exposed to heat. This heat is not sufficient to cause a burn, but causes a reticular, telangiectatic, pigmented dermatitis. The heating devices used during the cold climates, the laptops placed directly in contact with the skin are some of the causes for Erythema ab igne. This condition was first noticed among women who spent a longer period of time sitting in front of the fire places and electric heaters.
Erythema ab igne Symptoms
This skin changes seen under this Erythema ab igne skin condition is similar to solar damaged skin. It is because the heat which induces epithelial changes as a result of clonal mutation in the same way that ultraviolet light produces epithelial changes. It causes damage to the epidermis. The major symptoms noticed are skin rash, skin pigmentation or change in the color of the skin, thinning of the skin and the tissues located just below the skin, itching with burning sensations, etc. These are the major symptoms which are first noticed at the time of onset of the condition.
The duration for the repeated exposure to the heat on the skin determines the onset of the syndrome. It may vary from a few months to several years for the Erythema ab igne skin condition to present itself. The clinical explanation of the symptoms is that, as the skin is continuously exposed to heat a reticulated pigmentation with fixed legions, in other words rash with lacework like pattern with marked redness, is noticed on the skin. As these legions grow with time they become keratotic and bulla or sores starts to appear. The burning and itching sensation is felt at this stage. Squamous cell carcinoma (SCC) and Merkel cell carcinoma have been reported to have arisen from these legions even after 30 years after the onset of the Erythema ab igne disease.
Erythema ab igne Causes
Like mentioned before, Erythema ab igne skin condition is caused due to an over exposure to heat, but not enough to cause a burn, over a period of time. The area affected depends on the direction of the heat and the type or contour of skin. This skin condition has been given different names in accordance to the source of heat.
- Fire strains: It was first noticed on the legs or shins of women who sat for a long time in front of open fire, coal stoves and heaters. It affects the skin of those individually who sit in close contact with space heaters, steam radiators, and wood-burning stoves on a daily basis. Over exposure to car heaters and built in heaters in furniture like heated reclining chairs are also a major cause for these Erythema ab igne symptoms to appear.
- Hot water bottle rash: It affects patients with chronic backache or abdominal pain as they repeatedly apply heating pads or hot water bottles to relieve themselves from the pain, so this condition has been named hot water bottle rash.
- Toasted skin syndrome: This condition has been noticed on the face and palms of chefs and bakers; even silver smiths and jewelers are prone to Erythema ab igne (EAI) or toasted skin syndrome.
- Laptop thigh: In recent years major cases have been reported among laptop users. Laptops when rested on bare skin for a prolonged time block the ventilation fan situated beneath the laptop which results in production of excessive heat leading to Erythema ab igne. Thus this disease is also called laptop thigh as it has mainly been noticed on the left thigh and shin of laptop users.
Patients suffering from Cirrhosis, malnutrition, hypothyroidism, Hansen disease, anemia and lymphoedema are also prone to this condition. Additional major sources for the production of excess heat which may lead to Erythema ab igne or toasted skin syndrome are hot bricks, infrared lamps, wood stoves, microwave, etc. It should be noted that all the names given to Erythema ab igne skin condition are suggestive hence the symptoms and the treatment methods are the same.
Erythema ab igne Diagonsis
Physical diagnosis or noting the physical appearance of the skin is the first step in diagnosing the Erythema ab igne condition. The change in the skin color, thinning of the skin and reticulated erythema (red net like rash) are the physical changes which are noticed during diagnosis. In a particular laptop thigh case the patient showed an asymptomatic patch over the left anterior thigh. Physical examination revealed a brown to red, mildly erythematous, reticulated patch which was very well defined. Understanding the history and lifestyle of the patient it was discovered that the patient placed his laptop everyday on the left anterior thigh while at work. He discontinued do so only after he started experiencing discomfort from the heat emitted from the laptop.
Acanthosis nigricans, Livedo reticularis, etc are some of the diseases which can be mistaken for Erythema ab igne, thus a skin biopsy is essential to rule out any other condition and confirm this disease. A skin biopsy is essential especially in severe cases to rule out any possibilities of skin cancer.
Clinically epidermal vacuolation with abnormal elastic tissue are noticed on the epidermis. Melanophages and hemosiderin with fragmented collagen fibers are seen in the dermis. On rare occasion Merkel cell carcinoma may arise in the lesions. In short when heat induced skin damage is noticed on the epidermis, skin biopsy for Erythema ab igne skin condition should be performed.
Erythema ab igne Treatment
The first step for treating this condition after this disease is confirmed through biopsy is removing the source of the heat. That is either totally avoiding the source of heat or limiting the use of the source to cure the condition. Mild cases are cured within some months, just by following this simple step. There “s no specific line of treatment; every treatment depends on the severity of the condition. In some case applying topical tretinoin may help cure the disease while very severe cases will require laser treatments to improve the appearance of the skin. 5-Fluorouracil cream has also been reported to clear epithelial atypia in Erythema ab igne. However severe cases cannot be cured completely.
It has been noticed that when the patient is mildly affected by Erythema ab igne and no pigmentary change are seen then such conditions are cured by themselves, without any medical intervention, within a few months.
Care should be taken after the condition has been resolved as this disease cannot be cured completely. Monitoring regularly the affected area and reducing or elimination the source of the heat will prevent further development of the disease. Very rarely a complication like malignant degeneration may occur. The patient should be educated about the need of prompt action during the early stages of the Erythema ab igne disease and also after its been considerably cured.