Erythema ab igne

Erythema ab igne (EAI, also known toasted skin syndrome) is a skin condition caused by over exposure to infrared radiations. 

Initially, the skin in erythema ab igne patients is often mildly erythematous; however, after repeated heat exposures, the classic blue, purple, or brown reticulated hyperpigmentation develops.

A history of prolonged or repeated skin exposure to mild-to-moderate heat or infrared radiation that is below the threshold of thermal burn (less than 45°C) should raise suspicion. The duration of exposure varies from weeks to years. 

Examples include: 

• local application of hot water bottles or heating pads used for pain relief, 
• Direct exposure to the optic drive, battery, or ventilation fan of computers. Resting a laptop computer on the thigh (laptop computer-induced erythema ab igne).
• Repeated exposure to heated car seats, space heaters, or fireplaces. 
• Repeated or prolonged exposure to a heater is a common cause of this condition in elderly individuals.
• Occupational hazards of silversmiths and jewellers (face exposed to heat), bakers and chefs (arms)

                        Erythema ab igne as seen on the thigh after prolonged resting of laptop 

Clinical features: 

Erythema ab igne (EAI) is generally localized and usually well-demarcated, presenting with a reticulated macular pattern of erythema and hyperpigmentation . Cutaneous lesions are commonly asymptomatic, although patients may complain of pruritus or a slight burning sensation. Acute changes consist of a mild transient erythema that blanches.With repeated heat exposure, the lesion evolves into a more permanent, nonblanchable reddish-brown hyperpigmentation that may be associated with superficial atrophy. Telangiectasias and hyperkeratosis may also be present. Rarely, EAI can present with bullous lesions. EAI typically occurs on the legs, lower back, and abdomen but may occur on any and all body surfaces.

Complications; 

If the condition is severe and the skin pigmented and atrophic, resolution is unlikely. In this case, there is a possibility that a squamous cell carcinoma or a neuroendocrine carcinoma such as a Merkel cell carcinoma may form. If there is a persistent sore that does not heal or a growing lump within the rash, a skin biopsy should be performed to rule out the possibility of skin cancer.

Management

• Discontinuing contact with the heat source is the initial treatment of erythema ab igne. 
• If the area is only mildly affected with slight redness, the condition may resolve itself in a few months. 
• If the erythema ab igne lesions demonstrate pre-cancerous changes, the use of 5-fluorouracil cream has been recommended. 
• Abnormally pigmented skin may persist for years. 
• Treatment with topical tretinoin or laser may improve the appearance.