Are You Confident of the Diagnosis?
What should you be alert for in the history?
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, and direct exposure to the optic drive, battery, or ventilation fan of computers. (The left thigh is more commonly involved since the computer’s optic drive is located on this side.) Other potential heat sources are listed in Table I.
|Heated reclining chairs|
|Heating blankets/ pads|
|Hot water bottles|
Characteristic findings on physical examination
Erythema ab igne (EAI) is generally localized and usually well-demarcated, presenting with a reticulated macular pattern of erythema and hyperpigmentation (Figure 1). 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.
Expected results of diagnostic studies
Diagnosis is based largely on history and clinical presentation; therefore, biopsy and other laboratory tests are not usually performed unless there is suspicion for malignant change.
Histopathologic changes are significant for epidermal thinning accompanied by interface dermatitis with vacuolar alteration of the basal cell layer (Figure 2). As lesions progress, the epidermal atrophy becomes more pronounced, resulting in flattening of the rete ridges. Hyperkeratosis and dyskeratosis may be seen in some cases, similar to changes in actinic keratosis; as a result EAI has been referred to as “thermal keratosis.”
Dermal changes are significant for considerable dermal thinning, decreased fibrous content, and dilated vessels lined by enlarged and irregular endothelial cells with hyperchromatic nuclei. There is accumulation of elastic tissue most evident in the upper and mid-dermis. Basophilia is not a feature, unlike changes in solar elastosis. Pigment granules, made up of both melanin and hemosiderin are found lying freely in the dermis and within histiocytes.
The presence of characteristic lesions accompanied by a history of heat exposure to infrared radiation is sufficient for the diagnosis of EAI. The principal differential diagnosis includes:
Livedo reticularis. A blue-purple netlike discoloration of the skin that worsens with cold exposure. It results from an underlying disorder that affects the blood vessels, unlike EAI lesions which result from external thermal injury. The histology of livedo reticularis is dependent on the underlying etiology.
Poikiloderma may also be considered in the differential diagnosis, especially if EAI lesions present with telangiectasias and atrophy along with hyperpigmentation. If suspected, the various causes of poikiloderma (topical corticosteroid use, dermatomyositis, dermatoheliosis, early cutaneous T cell lymphoma, etc) must be elicited and can aid in distinguishing these disorders.
Who is at Risk for Developing this Disease?
Prior to the advent of central heating, EAI occurred in middle-aged to elderly women up to ten times more frequently than in men, as these individuals were more likely to utilize stoves or fireplaces for warmth. It is quite rare in children.
Risk factors include:
-Medical conditions with pain symptoms relieved by heating (ie, malignancy, musculoskeletal disorders, chronic pancreatitis, inflammatory bowel disease)
-Occupations/working environments in close proximity to a heat source (ie, bakers, silversmiths).
-Practice of resting laptops and other electronic devices on unprotected skin.
What is the Cause of the Disease?
Although the pathophysiology of EAI is not entirely understood, repeated heat exposure is thought to cause epidermal dysplasia. This exposure damages superficial blood vessels leading to hemosiderin deposition, accounting for the erythema and subsequent hyperpigmentation.
Systemic Implications and Complications
EAI has been linked with heat therapy for the treatment of disease-associated pain symptoms; therefore, it is important to determine if the heat source has been used to relieve pain.
Pain-causing diseases associated with EAI include musculoskeletal disorders, primary or metastatic malignancies, and gastrointestinal disorders such as pancreatitis, peptic ulcer disease, or inflammatory bowel disease.
Chronic changes in EAI may lead to the development of squamous cell carcinoma (SCC) or, in rare cases, Merkel cell carcinoma.
The risk of malignant transformation is thought to be highest in those exposed to hydrocarbon-fueled heat. Examples include:a Kang cancer in China and Tibet from heated-brick platforms (kangs), Kangri cancer in India caused by wicker baskets filled with hot coals (kangri), and Turf cancer in Irish women caused by standing close to peat fires. The latency period for malignant change is over 30 years.
Although these cancers are low-to-intermediate grade histologically, they are quite aggressive and recur or metastasize in over 30% of patients. They are ssociated with a poor prognosis. It is recommended that patients be monitored regularly, especially if EAI persists after the heat source has been removed. If there is clinical suspicion for malignant change (i.e. development of nodules or ulcerations), a biopsy should be performed.
Treatment options are summarized in Table II.
Eliminate the heat source
Optimal Therapeutic Approach for this Disease
There is no specific therapy for EAI, but the initial stages may be reversible if the heat source (Table I) is eliminated. if the heat source is being used for pain relief, alternative agents should be discussed.
Topical 5-fluorouracil (5-FU) may be used for chronic lesions, especially if precancerous changes are observed on histology. 5-FU has been shown to clear squamous atypia and may prevent the development of malignant transformation in EAI. Of note, controlled clinical trials have not been published to validate this effect. However, case reports recommend following similar treatment regimens as with actinic keratosis (once per day for up to 4 weeks as tolerated). If used to treat EAI on the face, patients should be advised to avoid eye contact.
Depigmenting agents such as topical tretinoin, hydroquinone, and other bleaching agents may be used for the pigmentary changes seen in EAI.
Laser therapy with ruby, alexandrite, or Q-switched Nd:YAG lasers may be helpful in treating the pigmentary sequalae of EAI. Photodynamic therapy may be useful if dysplastic keratinocytes are found on histology. However, its efficacy has only been investigated in actinic keratosis.
Patients with EAI should be advised to avoid further heat exposure, and must be followed for the resolution of hyperpigmentation (early lesions) and monitored for malignant change (chronic lesions). Suspicious lesions should be biopsied to rule out SCC and Merkel cell carcinoma. Patients should also be educated about the risk of malignancy, and should report any changes of appearance to their dermatologist for further evaluation. Treatment recommendations are outlined as above.
Unusual Clinical Scenarios to Consider in Patient Management
EAI may present with bullous lesions on rare occasions, and it is speculated that bullae develop in patients with coexisting lichen planus. Bullae usually develop over areas of skin exhibiting changes typical of EAI. Histologically, there is subepidermal separation of the epidermis, and direct immunofluorescence is usually negative. Patients should be managed in the same manner as the classical variant.
What is the Evidence?
Arnold, AW, Itin, PH. “Laptop computer-induced erythema ab igne in a child and review of literature.”. Pediatrics. vol. 126. 2010. pp. e1227-30. (A case report and review of literature that highlights laptop-induced erythema ab igne, a modern cause of infrared radiation. The authors describe a 12-year-old boy who played computer games for several hours per day with his laptop rested on his thighs. After a few months, the boy developed a brownish reticulated pigmentation that was described as livedo-like over his left upper leg.The discussion provides a review of EAI, including a brief history of thermally-induced SCC (Kang cancer, Kangri cancer, and Turf cancer). A review of literature demonstrated 9 previous cases of laptop-induced EAI which the authors compare to their case. This report concludes with the suggestion of providing a warning label on laptop packages.)
Finlayson, GR, Sams, WM, Smith, JG. “Erythema ab igne: a histopathological study”. J Invest Dermatol. vol. 46. 1966. pp. 104-8. (A histopathologic study that evaluates five skin biopsy specimens taken from three Caucasian patients with EAI. Briefly, the authors report epidermal atrophy with effacement of the rete ridges and vacuolization of the basal cell layer. In the dermis, a perivascular infiltration of histiocytes, neutrophils, and lymphocytes is seen. In addition pigment granules staining positively for iron (hemosiderin) and melanin are present.The authors focus their discussion on the dermal connective tissue. They describe an increase in narrow and disrupted fibers that are of the same morphology, enzyme susceptibility, histochemical properties, fluorescence, and refractility characteristic as elastic tissueAlthough the exact pathogenesis is unknown, the authors suggest that exposure to infrared radiation causes the lysosomes of the fibroblasts to rupture, releasing enzymes that degrade collagen within the dermis. This leaves the elastic tissue to accumulate in a dense band as seen on histology of the 5 cases described. As a result, the authors believe that EAI presents an example of secondary elastosis.)
Flanagan, N, Watson, R, Sweeney, E, Barnes, L. “Bullous erythema ab igne”. Br J Dermatol. vol. 134. 1996. pp. 1159-60. (This correspondence describes three cases of EAI that presented with bullous lesions. Each patient had a history of exposure to infrared radiation and developed bullae over areas of skin that exhibited typical EAI features including reticulated erythema and reddish-brown hyperpigmentation.Skin biopsies demonstrated subepidermal separation and mild perivascular lymphocytic infiltrate in the superficial dermis.Direct immunofluorescence was negative in two of the patients, but showed weak and patchy deposition of IgM along the dermo-epidermal junction in the third patient.In each patient, clinical improvement was noted upon removal of the heat source. The authors also discuss a possible association of bullous EAI with lichen planus.)
LoPiccolo, M, Crestanello, J, Toa, SS, Sciubba, J, Fernandez, C, Tausk, FA. “Facial erythema ab igne of rapid onset”. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. vol. 105. 2008. pp. e38-40. (A case report describing a 26-year-old female patient status post oral surgery for impacted molars who developed EAI on the right cheek and neck after applying warm compresses to the affected area. The reticular erythema resolved 12 days after discontinuing heat therapy.)
Naldi, L, Berni, A, Pimpinelli, N, Poggesi, L. “Erythema ab igne”. Intern Emerg Med. vol. 6. 2011. pp. 175-6. (A case report of an 86-year-old female on Coumadin for chronic atrial fibrillation who presented with a well-demarcated reddish-brown, netlike hyperpigmentation on both medial thighs. Routine blood examination revealed a microcytic anemia with iron deficiency and an elevated ESR, suggesting a diagnosis of livedo reticularis secondary to systemic disease. However, after uncovering a history of using a hot water bottle on her thighs, the diagnosis of EAI was made.)
Page, EH, Shear, NH. “Temperature-dependent skin disorders”. J Am Acad Dermatol. vol. 18. 1988. pp. 1003-19. (An extensive review of temperature-dependent skin disorders ranging from cold-induced conditions (chilibans, livedo reticularis, acrocyanosis, etc) to disorders caused by heat. The authors provide a brief discussion on thermoregulation in the skin and the physiologic responses to extremes of temperature.)
Riahi, PR, Cohen, PR, Robinson, FW, Gray, JM. “Erythema ab igne mimicking livedo reticularis”. Int J Dermatol. vol. 49. 2010. pp. 1314-7. (A case report of a 19-year-old Asian female presenting to her primary care physician with a 2-month history of a netlike hyperpigmentation on the lower extremities. Livedo reticularis was initially suspected by the internist prompting referral to dermatology, who elicited a history of using a large space heater to keep warm while working.)
Sahl, WJ, Taira, JW. “Erythema ab igne: treatment with 5-fluorouracil cream”. J Am Acad Dermatol. vol. 27. 1992. pp. 109-10. (This case report describes a 72-year-old black female presenting with reticulated hyperpigmentation in the popliteal fossae corresponding with a history of frequent exposure to a gas-fired heat source. A biopsy was taken, and revealed changes consistent with EAI as well as scattered dysplastic keratinocytes. As a result, the patient was treated with a 2-week course of 5-FU. Biopsies at 6 weeks and 5 months demonstrated an absence of atypia.)
Shahrad, P, Marks, R. “The wages of warmth: changes in erythema ab igne”. Br J Dermatol. vol. 87. 1977. pp. 179-86. (This case report describes a 72-year-old black female presenting with reticulated hyperpigmentation in the popliteal fossae corresponding with a history of frequent exposure to a gas-fired heat source. A biopsy was taken, and revealed changes consistent with EAI as well as scattered dysplastic keratinocytes. As a result, the patient was treated with a 2-week course of 5-FU. Biopsies at 6 weeks and 5 months demonstrated an absence of atypia.)
Smith, ML, Bolongia, J, Jorizzo, J, Rapini, R. “Environmental and ssorts-related skin diseases”. Dermatology e-dition. 2008. (This chapter focuses on environmental and sports-related skin disorders, including thermal burns and heat-related illnesses such as: heat edema and heat stroke, burns from fluoroscopy and magnetic resonance imaging, and injury due to electricity, cold, water, or chemical exposure, among many other disorders. The section on EAI briefly discusses epidemiology, pathogenesis, clinical and histologic features, and differential diagnosis. The author highlights treatment of EAI, specifically removal of the heat source and 5-FU.)
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