When A Senior Presents With A Large, Irregular Pigmented Lesion On The Shin

An 86-year-old woman presented to the clinic with complaints of an ingrown toenail. However, the physical exam revealed a large lesion on the anterior right shin. The patient stated the lesion had been there for “a long time.” She had a history of high blood pressure and peripheral vascular disease. In fact, she had suffered an amputation of the left leg due to ischemia. There was no personal or family history of skin cancer, and the lesion did not bother the patient at all.

The physical exam revealed a large, asymmetrical pigmented lesion on the anterior right shin measuring 3 x 4 cm in diameter. It had multiple shades of brown and black in it, and was elevated in certain spots. In the areas of elevation, the lesion had a cerebriform pattern and almost looked stuck-on. However, there were other areas that were not elevated but simply darkly pigmented. In these areas, though, the border was very irregular.

Due to the irregularity of the lesion and the concern that the patient had already lost one leg, I determined a biopsy was necessary to rule out malignancy. The hope was to catch it before it became invasive, which could lead to amputation. However, the patient also had very weak pedal pulses with delayed capillary refill times in the toes and diminished skin quality. Therefore, I first sent her to a vascular lab to confirm that her circulation was sufficient to heal the biopsy.

Once this was done, she came back to the clinic and my colleague anesthetized and prepped the area of the lesion. Under sterile conditions, my colleague performed a 3 mm punch biopsy in three places in the areas of most irregularity and elevation. She wore a compressive dressing for three days. Afterward, the patient was allowed to remove the dressings, clean the area and apply a topical antibiotic and bandage every day. We sent the lesion to pathology for histological examination.

Key Questions To Consider

1. What pathologies are in the differential diagnosis of this lesion?
2. What is the correct diagnosis of this lesion?
3. What is the etiology of this lesion?
4. What is the prognosis and malignant potential with this lesion?
5. What is the preferred treatment method?

Answering The Key Diagnostic Questions
1. Melanoma, pigmented basal cell carcinoma, atypical nevus, seborrheic keratosis, verruca vulgaris
2. Seborrheic keratosis    
3. The etiology is unknown at this point although genetic predisposition is a major factor.
4. These lesions have no malignant potential and are mainly of cosmetic concern.
5. Cryotherapy is the most common method of treatment although a shave excision allows for biopsy if there is concern for malignancy. Any method can cause scarring and post-inflammatory hyperpigmentation.

What You Should Know About Seborrheic Keratoses

Seborrheic keratoses are the most common benign cutaneous neoplasms along with nevi.^1–3 They are a benign proliferation of immature keratinocytes that present clinically as well-demarcated round or oval lesions with a verrucous surface and classical “stuck-on” appearance. Most commonly found on the trunk, face or upper extremities, these lesions usually appear in people older than 50 either as a solitary lesion or in groups, sometimes covering a body surface almost entirely. These “barnacles of life” are usually asymptomatic but irritation or trauma can make them pruritic and painful. With more irritation, they can get red and swollen, and even become an oozing mass with a friable surface. Of note to podiatric physicians, seborrheic keratoses do not occur on the soles of the feet.

The etiology of these lesions is currently unknown. However, genetic predisposition is a major factor. Even the pathogenesis is incompletely understood as evidence of a role of cumulative ultraviolet radiation exposure or human papillomavirus infection is inconsistent. Mutations in fibroblast growth factor receptor 3 and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) are present in seborrheic keratoses but their role in pathogenesis is unknown.

Despite their nasty appearance, these lesions have no malignant potential and usually are only of cosmetic concern. That being said, they can be associated with other malignancies including gastrointestinal and lung cancer.⁴ The sign of Leser-Trélat is an indication of these cancers and it consists of a sudden appearance of multiple seborrheic keratoses along with skin tags and acanthosis nigricans. Inflammation of preexisting lesions can occur during chemotherapy as well.

Although they have no malignant potential, seborrheic keratoses can resemble melanoma due to their irregular borders, large size and variable pigmentation. A hand lens or dermatoscope can help even the most experienced practitioner confirm the diagnosis as seborrheic keratoses have quite a few identifying features, including the following: small keratin-filled “horn” cysts, dark comedo-like keratin plugs, milia cysts and fissures/ridges showing a cerebriform pattern.⁵ If the diagnosis is still in question, a biopsy will settle the matter with histology confirming the well-demarcated proliferation of keratinocytes with characteristic horn cysts with or without a dermal lymphocytic infiltrate. Biopsy is particularly warranted when lesions are extremely large, rapidly growing or ulcerated.

Moreover, as I said before, these lesions do not occur on the soles of the feet. Therefore, one should pursue a biopsy for any irregular lesion in this area regardless of any similarities to seborrheic keratoses.

Pertinent Treatment Considerations

As seborrheic keratoses are completely benign with no malignant potential, treatment is not required. However, patients will frequently seek treatment due to cosmetic concerns and/or irritation and pain. The most common treatment clinicians utilize is cryotherapy, which one can easily do in the office and which usually causes the lesion to blister and fall off.

Another easy method is curettage with a dermal curette. If the physician has access to a cautery device, electrodesiccation both removes the lesion and provides immediate hemostasis. If the diagnosis is questionable, a shave biopsy/excision both removes the lesion and preserves it for histological examination. Laser removal is an option but does not have a lot of research.

Common complications after removal or destruction of the lesions include post-inflammatory hyper- or hypopigmentation, especially in darker skin, and pain or irritation during the healing process, which one should consider if the patient is only having the lesion removed for cosmetic purposes.

In Conclusion

Seborrheic keratoses are benign but cosmetically displeasing skin lesions that present mostly in patients over 50 years of age. While their etiology is unknown, UV radiation is a suspected cause and genetic predisposition is a major factor. Treatment usually consists of cryotherapy or curettage, but if the diagnosis is questionable, a shave biopsy both removes the lesion and preserves it for histological examination.

Dr. Vella is in private practice in Gilbert, Ariz.

References

1.     Goldstein BG, Goldstein AO. Overview of benign lesions of the skin. UpToDate.com. Available at https://www.uptodate.com/contents/overview-of-benign-lesions-of-the-skin .
2.     Vlahovic TC, Schleicher SM. Skin Disease of the Lower Extremities: A Photographic Guide. HMP Communications, Malvern, PA, 2012, pp. 86–87.
3.     Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy, Fifth Edition. Chapter 20: Benign skin tumors, Mosby Elsevier, St Louis, 2010, pp. 776-783.
4.     Arbiser JL, Bonner MY. Seborrheic keratoses: the Rodney Dangerfield of skin lesions, and why they should get our respect. J Invest Dermatol. 2016; 136(3):564-66.
5.     Carrera C, Segura S, Aguilera P, et al. Dermoscopy improves the diagnostic accuracy of melanomas clinically resembling seborrheic keratosis: cross-sectional study of the ability to detect seborrheic keratosis-like melanomas by a group of dermatologists with varying degrees of experience. Dermatology. 2018; Epub ahead of print.