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Dermatology Diagnosis

When A Patient Presents With Lesions And Discolored Shins

We recently examined a patient who complained of discolored legs. She was 92 years of age and had discolored shins with multiple white and black lesions that began when she was 60 years of age.

The patient reported growing up in rural South Carolina and subsequently moving to northern Ohio at the age of 19. Her childhood home lacked central heating and a potbellied stove kept it warm in the winter months. She admitted to many hours spent sitting close to the stove preparing food and reading. It is also important to note that she grew up wearing skirts rather than pants.

Her past medical history included controlled hypertension, hyperlipidemia and type 2 diabetes with peripheral neuropathy. The surgical history included a hysterectomy and cataract surgery. Significant physical findings included non-palpable pedal pulses with monophasic waveforms and ankle brachial indices (ABI) of 0.73 on the right and 0.86 on the left. Dermatological examination revealed multiple hypopigmented macules, patches and plaques covering the anterior shins.

A dermoscopy examination demonstrated white collagen fibrosis without a vascular network in the areas of depigmentation. In addition, several black and brown, asymmetric hyperkeratotic plaques with irregular borders were present. A dermoscopy examination of these black plaques revealed pigmented seborrheic keratoses with characteristic moth-eaten borders but no melanoma specific structures. A dermatology consultation confirmed the diagnosis of multiple benign pigmented seborrheic keratoses.

Key Questions To Consider

1. What unique characteristics of this patient gave clues to the condition?
2. What is this condition?
3. What is the differential diagnosis?
4. How can one prevent this condition?

Answering The Key Diagnostic Questions

1. In childhood, the patient spent many hours next to a potbellied stove and wore skirts rather than pants.
2. Erythema ab igne, also known as toasted shins
3. Livedo reticularis, seborrheic keratosis, actinic keratosis, squamous cell carcinoma
4. Patients need constant reminders of the risk of developing skin cancer with overexposure to heating pads, outdoor fire pits, laptops, space heaters and indoor fireplaces.

What You Should Know About Toasted Shins And Erythema Ab Igne

Infrared radiation has been long known to damage skin cells. Research has shown that chronic exposure to infrared radiation in the form of heat causes acute and chronic changes.1 The “toasted shin” presentations that are most common today are late manifestations of changes in patients who had been chronically exposed to infrared radiation from potbellied stoves or fireplaces in homes without central heating. This infrared radiation causes changes in skin cells starting with a mild transient, red, reticulated rash that resembles a fishnet or lacy network. It is more often visible in elderly patients who were chronically exposed to using open fire heating. Historically, it has been present in metalsmiths on their faces and palms since they were exposed to intense infrared radiation from working with open flames.2

However, younger patients are not always spared. There are new reports of “road warriors” or frequent flyers who are waiting for flights while working with their computers on their laps and exposing their skin to sustained high amounts of infrared radiation heat damage.3 Infrared radiation damages the epidermis and superficial vascular plexus with temperatures that can reach between 43 and 47°C.1 Erythema ab igne develops with temperatures insufficient to cause burns but still damaging enough to lead to chronic cutaneous changes.4

Although erythema ab igne can present on any body surface, most cases present on the back or thighs, correlating with areas where heating pads are commonly in use.5 Erythema ab igne acutely appears in its initial stage as transient, blanchable erythema followed by progression to a reticular pattern of hyperpigmentation with epidermal atrophy and telangiectasias after continued heat exposure.6 The changes are generally asymptomatic. There appears to be no racial predisposition to developing erythema ab igne. However, McCall and Chen suggest that erythema ab igne was more common in females with exposure to open fire heaters than males since men usually wore long pants and women relied on the open fires to keep their legs warm during the winter months.7

Since there are no current laboratory studies to aid in the diagnosis of erythema ab igne, we must rely on clinical suspicion and cutaneous biopsy to confirm the diagnosis as well as rule out underlying malignancy. Erythema ab igne appears similar to sun damage histologically.8 Skin biopsies may demonstrate a range of findings from a sparse perivascular infiltrate in early lesions to epidermal atrophy, telangiectasias, keratinocyte atypia or hemosiderin deposition. Chronic presentations can demonstrate increased elastin fibers that clinicians can identify with special stains.9 Advanced cases such as those from potbellied stoves, fireplaces, open fires or long-term heat exposure from prolonged laptop computers triggers focal vacuolization, hyperkeratosis and dyskeratosis with possible epidermal dysplasia.

A Guide To The Differential Diagnoses

Like erythema ab igne, livedo reticularis also can present with a red-blue mottled discoloration. It affects more women than men. Livedo reticularis has been associated with many different disorders. Researchers once thought the condition to be a solely vasospastic disease but recent literature reports that drug-induced causes, including ergot-derived medications used for migraines and cocaine, can induce livedo reticularis.10

Seborrheic keratosis previously had the term “senile keratosis.” This presents as stuck-on common hyperkeratotic plaques. They are benign cutaneous lesions with an unknown origin. They are often pigmented. Evaluating seborrheic keratosis with the A-E clinical criteria helps detects lesions that need biopsy to rule out underlying malignancy.11 It is reassuring to observe their generally uniform color and symmetry.

Actinic keratosis is the most common benign lesion on the skin with malignant potential.12 It is important to note that actinic keratoses are similar in character to squamous cell carcinoma. They are due to ultraviolet damage to epidermal DNA. Histologically actinic keratoses are confined to the epidermis without dermal invasion. It is important to diagnose, treat and monitor actinic keratoses correctly when they first present.11 Transformation into squamous cell carcinoma is more common in patients with skin prototypes I and II.12 A small percentage of the actinic keratoses reportedly transform into squamous cell carcinoma.11 These transformed lesions extend into the dermis and proceed to metastasize through the bloodstream. Researchers have shown that actinic keratosis that presents on the trunk and lower extremity has a poorer prognosis.11

Squamous cell carcinomas are the second most common malignant skin cancer. Thirteen percent of squamous cell carcinomas present on the extremities. They can grow unabatedly and destroy adjacent skin, cartilage and bone. If they are not removed, squamous cell carcinomas can carry a poor prognosis. Potential sites for metastasis include the lungs, liver, brain, skin or bone.13 Ultraviolet light exposure, antioxidants and non-steroidal anti-inflammatory drugs (NSAIDs) including aspirin have been linked as possible risk factors.13 The presentation of squamous cell carcinoma may include non-healing ulcerations in sun-exposed area on the body. Squamous cell carcinomas may appear as plaques or patches on skin. Therefore, it is important to be vigilant for any progressive lesions or ulcerations.

Key Pointers On Preventing Erythema Ab Igne

Erythema ab igne is an asymptomatic condition caused by heat exposure whether it be infrared or ultraviolet radiation. Erythema ab igne is Latin for “redness from fire.” Erythema ab igne is consistent with the acute stages while the late stages take on the appearance of toasted shins. Both are historically associated with exposure to open fires and wood-burning stoves, but more modern causes are related to technologically advanced sources like heating pads, electric blankets, hot water bottles, space heaters, heated car seats and laptop computers.1,6

The acute and chronic stages may not be recognizable unless the examiner is familiar with the condition. Erythema ab igne is important to recognize because of the increased risk of skin cancer development. Although erythema ab igne could present on any surface of the body, today most cases of erythema ab igne occur on the back or thighs, correlating with areas where patients commonly use heating pads.5 Morrison and colleagues reported a case of erythema ab igne on the feet triggered by a space heater used to keep a patient’s feet warm while working at a computer.14

With increased air travel and “road warriors,” the incidence of infrared radiation damage has also increased.15 Accordingly, it is important to investigate skin damage due to infrared/ultraviolet radiation whether it is from laptops or open fire primarily because of its increased risk of squamous cell carcinoma.3 In their 2001 study, McCall and coworkers showed that out of 35 African-Americans, three cases of squamous cell carcinoma were due to a prior diagnosis of erythema ab igne.7

Authors have reported cutaneous lymphoma and Merkel cell (neuroendocrine) carcinoma combined with squamous cell carcinoma in erythema ab igne.1,16 Topical treatments with tretinoin and hydroquinone have been in use for persistent hyperpigmentation, and epithelial atypia may respond to topical therapy with 5-fluorouracil.

Since erythema ab igne is preventable with patient education and is not easily treatable using topical medication, clinicians should consistently remind patients of the risk of developing skin cancer with overexposure to heating pads, outdoor fire pits, laptops, space heaters and indoor fireplaces as well as general recommendations to continually use topical sunscreens to protect against overexposure from the sun.5

Dr. Bodman is an Associate Professor at the Kent State University College of Podiatric Medicine. He is board-certified by the American Board of Podiatric Medicine.

Mr. Mekhail is a fourth-year podiatric medical student at the Kent State University College of Podiatric Medicine.


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  10. Herrero C. Diagnosis and treatment of livedo reticularis on the legs. Practical Dermatology. 2016; 99(2016):598-607.
  11. Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy, Sixth Edition. Elsevier, Philadelphia, 2016, pp. 784-785.
  12. Frost CA, Green AC, Williams GM. The prevalence and determinants of solar keratoses at a subtropical latitude (Queensland, Australia). Br J Dermatol. 1998; 139(6):1033-9.
  13. Lim JL, Asgari M. Epidemiology and risk factors for squamous cell carcinoma. UptoDate. Available at . Published December 2016.
  14. Morrison M, Cotton J, LaFond A. Reticulated erythematous patch on teenager’s foot. J Fam Pract. 2014; 63(9):537–539.
  15. Bachmeyer C, Bensaid P, Bégon E. Laptop computer as a modern cause of erythema ab igne. J Eur Acad Dermatol Venerol. 2009; 23(6):736-737.
  16. Jones CS, Tyring SK, Lee PC, Fine JD. Development of neuroendocrine (Merkel cell) carcinoma mixed with squamous cell carcinoma in erythema ab igne. Arch Dermatol. 1988; 124(1):110–113.
Dermatology Diagnosis
Myron Bodman, DPM, and Andrew Mekhail, BS
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