Describe erythema ab igne.

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Erythema Ab Igne: Clinical Description

Erythema ab igne (EAI), also known as "toasted skin syndrome," is a distinctive cutaneous reaction characterized by reticular (net-like) hyperpigmentation with erythema, epidermal atrophy, and telangiectases that develops from chronic, repeated exposure to infrared heat or moderate thermal sources at temperatures insufficient to cause an acute burn. 1, 2

Clinical Presentation

Primary Morphology

  • Reticular (lacy, net-like) pattern of hyperpigmentation is the hallmark feature, appearing as a web-like or fishnet distribution on the skin 1, 3, 2
  • Persistent dusky erythema interspersed within the hyperpigmented areas 1, 4
  • Epidermal atrophy causing thinning of the skin surface 1, 4
  • Telangiectases (visible dilated blood vessels) scattered throughout the affected area 1, 4

Variant Presentations

  • Bullous form: Rarely, bullae (blisters) and crusts can develop within the reticular pigmented areas, representing a well-defined but uncommon variant 4
  • Hyperkeratotic lesions: In longstanding cases, thickened, scaly lesions may emerge within the affected areas 3

Distribution Patterns

  • Most commonly affects lower extremities (legs, particularly shins and knees) and the back 1, 5
  • Asymmetric distribution corresponding to the site of heat exposure 2
  • Can occur on any body surface with repeated thermal contact 5

Causative Heat Sources

Historical Sources

  • Open fires and coal stoves (traditional causes) 1
  • Industrial heat exposure in bakers and factory workers 2

Modern Sources

  • Heating pads applied repeatedly to the same area 1
  • Laptop computers resting on thighs or abdomen 1, 2
  • Space heaters positioned near legs or under desks 2, 5
  • Electric heaters in close proximity to skin 4
  • Heated car seats with prolonged use 2
  • Heated furniture 1
  • Hot water bottles 5

Pathophysiology

The reticular hyperpigmentation results from heat-induced degeneration of elastic fibers and basal keratinocytes, causing melanin release into the dermis. 2 The repeated thermal insult at subburn temperatures (typically from infrared radiation) damages dermal structures without causing immediate tissue necrosis. 1

Clinical Course and Prognosis

  • Early-stage lesions may resolve spontaneously after removal of the heat source 2, 5
  • Delayed diagnosis or persistent exposure leads to permanent pigmentation that does not fade even after heat source removal 2
  • The condition progresses gradually over weeks to months of repeated exposure 3, 4

Malignant Transformation Risk

A critical concern with longstanding EAI is the potential for malignant transformation, making this more than just a cosmetic pigmentary disorder. 1

Histologic Warning Signs

  • Squamous atypia with basal layer crowding in later stages 1
  • Loss of normal epidermal maturation throughout the epidermis 1

Associated Malignancies

  • Squamous cell carcinoma (most commonly reported) 1, 2
  • Basal cell carcinoma 2, 5
  • Merkel cell carcinoma 2

Clinical Implication

Patients with longstanding EAI, particularly those with hyperkeratotic lesions developing within the pigmented areas, require skin biopsy to exclude pre-malignant or malignant transformation. 3 The risk increases with duration of exposure and persistence of lesions. 2

Diagnostic Approach

Clinical Diagnosis

  • Diagnosis is primarily clinical, based on the characteristic reticular hyperpigmentation pattern and documented history of chronic heat exposure to the affected area 3, 5
  • The temporal relationship between heat source use and lesion development is key 4, 5

When to Biopsy

  • Hyperkeratotic lesions emerging within EAI require biopsy to rule out malignant change 3
  • Longstanding lesions with atypical features warrant histologic evaluation 1
  • Any nodular or ulcerated areas developing within the pigmented region 1

Management

Primary Intervention

Immediate and complete removal of the causative heat source is the essential first step. 2, 5 This alone may lead to resolution in early cases. 2

Monitoring

  • Early-stage lesions: Observe for spontaneous resolution after heat source removal 2, 5
  • Persistent pigmentation: Counsel patients that longstanding changes may be permanent despite cessation of exposure 2
  • Surveillance for malignancy: Long-term follow-up for patients with persistent lesions, particularly those with histologic atypia 1

References

4
Research

Bullous erythema ab igne.

Dermatology online journal, 2003

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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