38-Year-Old With Rash After Heating Pad Use

Differential Diagnosis

• Intravascular large B cell lymphoma
• Erythema ab igne
• Livedo reticularis
• Polyarteritis nodosa

Diagnosis

The correct diagnosis in this case is erythema ab igne (EAI), a disorder of hyperpigmentation caused by prolonged exposure to heat. Heat exposure produces cutaneous hyperthermia, which in turn results in histopathologic changes similar to those seen in sun-damaged skin. Patients who report long-term use of heating pads or electric blankets may experience EAI. Heat exposure from a fireplace or even a laptop computer can also trigger the disorder.

What to Look For

• The rash appears as mottled, reticulated, pink, reddish, or violaceous patches that eventually become brown from melanin deposition
• While usually asymptomatic, there may be pruritus or mild burning paresthesias
• Rarely, vesicles or bullae have been described in affected areas

Pearls for Urgent Care Management

• Treatment is removal of the heat source
• Skin changes usually clear without further intervention in weeks to months, however, some may become permanent

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