Erythema ab igne is a cutaneous rash characterized by a reticulated pattern of erythema and hyperpigmentation. This dermatosis is caused by repeated exposure of direct heat or infrared radiation to a person’s skin, often from occupational exposures or use of heating pads. While the rash is most often benign, its presence can be an indication of chronic inflammation or, less commonly, systemic illness and should prompt further investigation. Furthermore, careful inspection of the rash may yield evidence of possible pre-malignant transformation and should prompt referral for biopsy, if indicated.
Historically, this rash has correlated with heating sources emitting infrared radiation such as fires, wood-burning stoves, and kerosene lamps; however, with the advent of central heating sources, it is seen less commonly. Common causes today include localized heating sources such as laptop computers, warm water bottles, heating pads, and space heaters. Patients at risk include patients with chronic pain who often use these heat sources, for example, heating pads, as a form of relief. Literature has also highlighted the presence of erythema ab igne in younger populations from the use of laptop computers.
Historically, erythema ab igne affects women more often than men. This skin finding can be present at any age as it correlates with exposure to infrared radiation. Importantly, there is a high correlation with middle-aged to elderly patients who suffer from chronic pain as they often use heating pads as an adjunct to their treatment regimen.
Erythema ab igne occurs from repeated exposure of direct heat or infrared radiation usually developing over the course of weeks to years at temperatures that are insufficient to cause significant thermal burns. The pathophysiology of the condition is not fully understood; however, the hypothesis is that the repeated heat exposure damages superficial blood vessels leading to hemosiderin deposition and subsequent hyperpigmentation. Continued exposure may eventually lead to hyperkeratosis and hyperelastosis of the affected skin.
Changes in the skin at the microscopic level typically incur from cumulative and prolonged exposure to infrared radiation. Microscopic changes are also dependent on the type of heat source. Biopsies are relatively non-specific and can show a range of characteristic findings including atrophy, hemosiderin deposition, telangiectasias, hyperkeratosis, and increased elastin. Given this, biopsies appear to be most useful for the exclusion of more serious conditions such as Merkle cell carcinoma and squamous cell carcinoma which may present with similar skin findings.
Patients may seek medical care for this dermatosis but often occurs as an incidental finding on physical exam. Patients typically present with a chronic history of using a heating source, such as a heating pad. On physical exam, the skin will commonly demonstrate a reticular, or net-like pattern of blue-gray discoloration with associated erythema. Initially, the affected area presents as blanching erythema and with time and repeated exposure results in a non-blanching, abnormally pigmented area. Patients are usually asymptomatic, but some may complain that the affected area burns itches, or stings.
Erythema ab igne is mostly a clinical diagnosis that raises suspicion given the relevant history and characteristic skin manifestations. Long-standing disease in the presence of ulcerations, hyperkeratosis, or bullae should prompt further evaluation by a dermatologist, as rarely this finding can be associated with malignant transformation of squamous cell carcinoma or Merkel cell carcinoma. As patients often are applying heat to areas of chronic pain, further history should also be obtained from the patient to investigate the cause of the patient's chronic pain as they may need a further referral for this as well.
The primary treatment of this disease entity is the removal of the offending heat source. The resulting abnormal pigmentation of affected areas may resolve over months to years; however, permanent hyperpigmentation or scarring may persist. If epidermal atypia is suspected, then regular skin examinations are recommended. Topical 5-fluorouracil has also been shown to treat epithelial atypia if present as well. Other therapies such as topical tretinoin or hydroquinone can be useful in treating persistent hyperpigmentation. Rarely, these lesions can lead to the development of squamous cell carcinoma and Merkel cell carcinoma. Patients with persistent lesions should undergo monitoring for possible malignant transformation. Biopsies are warranted for evolving lesions and/or the presence of ulcerations, hyperkeratosis or bullae.
Erythema ab igne should be a consideration in the differential diagnosis for dyspigmented reticular dermatoses. Other diagnoses for this pattern of rash include:
A key feature that can distinguish erythema ab igne from other reticular rashes is its presentation in the setting of chronic heat exposure as livedo reticularis and cutis marmorata are often present with exposure to cold and other rashes present without a history of heat exposure altogether.
Erythema ab igne holds a favorable prognosis with the removal of the offending heat source and repeated exposures are limited. If prolonged exposure continues, there is a risk of permanent dyschromia of the skin, as well as the potential for transformation into pre-malignant or malignant skin lesions.
Complications are rare; however, malignant transformation to squamous cell carcinoma or Merkel cell carcinoma have been reported in the literature with signs of hyperkeratosis or ulceration occurring as secondary, premalignant changes.
Patient education on heat as a cause of this disease is essential for the treatment and to prevent a recurrence. Patients diagnosed with this disease due to occupational exposure need specific guidance on how to prevent exposure and optimize outcomes. In patients with chronic pain, alternatives therapies for pain relief should be advised to prevent repetitive exposures.
An interprofessional approach to erythema ab igne is recommended. Erythema ab igne is a preventable skin dermatosis, and the importance of patient education is critical in preventing disease progression. The majority of these patients will present to the primary care provider or nurse practitioner.
Heating pads and water bottles are commonly used in the management of chronic pain and can potentially lead to the development of erythema ab igne. Physicians should be aware of the presentation of erythema ab igne, as well as other mimicking conditions such as livedo reticularis, cutis marmorata, physical abuse and be aware of the risks for malignant transformation in areas of repeated heat exposure. Furthermore, a careful history should be obtained to rule out other systemic symptoms that could be indicative of other more serious pathologies causing the patient’s chronic pain. Long-standing erythema ab igne in the presence of other secondary changes such as ulceration or hyperkeratosis should prompt a dermatologist referral for biopsy and further management.
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