Peculiar pigmented patch

March 7, 2015

Clinical Vignette

An 18-year- old girl complains of a peculiar brown patch on her right anterior thigh for 3 weeks. With bikini season around the corner she wants it gone! She does admit to leaning her laptop on her right thigh for a few hours each day. What's the diagnosis?

Diagnosis and Clinical Presentation

Diagnosis: Erythema ab igne (EAI) The reticulated brown patch on her right thigh is typical of erythema ab igne (EAI). Clinically EAI presents as persistent, reticulated, erythematous, telangiectatic patches with hyperpigmentation. Although the pathogenesis of EAI is poorly understood, It is known to be associated with chronic and repeated exposure to moderate heat from an external heat source. The heat exposure does not have to be of long duration and may be as short as a few weeks (1). Women are more commonly affected by EAI than men. Open fires have been reported as a cause of EAI but an infrared source such as a heating pad or hot water bottle is the more usual precipitant. As such EAI historically was noted in patients with chronic pain conditions requiring use of these therapies (2). A newly recognized etiology of EAI caused by the warm battery of a laptop computer is illustrated by our patient (3,4). The diagnosis is largely based on history and physical exam findings. A thorough workup can include a punch biopsy if the diagnosis is uncertain. Histologic findings are often non-specific and may include epidermal atrophy, melanin incontinence, collagen degeneration, and occasionally keratinocytic and melanocytic atypia (5).


In most cases these lesions are benign with the only morbidity being secondary to the unfavorable cosmetic appearance. It is important to inform patients that discontinuation of heat exposure is of paramount importance and that hyperpigmentation may resolve within several months should they avoid heat exposure to the affected area. With repeated heat exposure the hyperpigmentation and atrophy may become permanent (4,5). Moreover, there are rare reports of squamous cell carcinoma arising in these lesions especially after many years of infrared exposure (6), and patients should be counseled accordingly.

Our Patient

Our patient was advised to protect her skin from heat exposure from her laptop and other potential sources and reassured that the diagnosis was made early and that the lesions might resolve before the end of the summer swim season.


This case demonstrates a newly recognized etiology for erythema ab igne. It is important for physicians to be able to recognize novel heat sources as potential causative agents for this entity and to instruct their patients to discontinue such exposure.


  1. Page EH, Shear NH. Temperature-dependent skin disorders. J Am Acad Dermatol. 1988; 18:1003-1019.
  2. Warycha, Melanie. What is your diagnosis? Erythema Ab Igne. Cutis. 2006 78:392, 395.
  3. Bilic, Maya and Brian Adams. Erythema ab igne induced by a laptop computer. J Am Acad Dermatol. 2004; 973-4.
  4. Mohr MR, Scott KA, Rariser RM. Laptop computer induced erythema ab igne: a case report. Cutis. 2007;79:59-60.
  5. Page EH, Shear NH. Temperature-dependenet skin disorders. J Am Acad Dermatol. 1988; 18: 1013-4.
  6. Arrington JH, Lockman DS. Thermal keratoses and squamous cell carcinoma in situ associated with erythema ab igne. Arch Dermatol . 1979; 115:1226-8.



Body Site

Anatomic Depth