10: Benign brown-black and pigmented skin growths

Abstract:

The vast majority of brown-black skin growths are benign; however, they are frequently a cause for concern among patients who believe they may have a malignant melanoma. The ability to recognize common benign brown-black skin growths can spare patients anxiety and the scar from a biopsy. This chapter reviews common brown-black skin growths that are not discussed elsewhere in this book.

Key terms:

seborrheic keratosis

café au lait macules

dermatofibroma

congenital melanocytic nevus

acquired digital fibrokeratoma

blue nevus

Chapter outline

Seborrheic Keratoses
Acquired Digital Fibrokeratoma
Acrochordon
Blue Nevus
Café-Au-Lait Macules
Dermatofibroma

Seborrheic keratoses

Layla Kazemi and Afton Chavez

Clinical features

• Seborrheic keratoses (SKs) are common benign skin lesions found in nearly all older individuals.
• They typically begin to appear during the fourth decade of life and then continue to develop throughout one’s lifetime.
• They can develop anywhere except the palms, soles, and mucosal surfaces.

• They are found most often on the head and neck, extremities, and trunk, especially the upper back and inframammary region (in women).
• SKs are macular, papular, or verrucous lesions and often have a keratotic plugging, a waxy stuck-on appearance, and/or overlying scale.

• They typically evolve from a macule and may progress to become papular or verrucous.
• They are most commonly light brown but may appear white to waxy yellow to brown-black in color, and within the same lesion, there may be a marked variation in color.
• SKs are occasionally solitary but more commonly present as multiple, pigmented, sharply demarcated lesions.
• Individual lesions may be of any size but usually measure about 1 cm in diameter, although they can become quite large (i.e., greater than 5 cm) in diameter.
• SKs may become inflamed or irritated because of friction or trauma or, rarely, from a secondary bacterial infection.

• Irritated or inflamed lesions may become tender, pruritic, erythematous, crusted, and rarely, pustular.
• There are a few conditions associated with an abrupt appearance or increase in the number of SKs: pregnancy, coexisting inflammatory dermatoses, and malignancy. This would be followed by regression once the condition resolves.

Differential diagnosis

The differential for SKs includes solar lentigo, verruca vulgaris, condyloma acuminatum, Bowen disease, squamous cell carcinoma (SCC), melanocytic nevus, melanoma, acrochordon, and tumor of the follicular infundibulum.

• Solar lentigines are neither keratotic nor elevated, but over time, they can develop into SKs.
• Verrucae and condylomata acuminata are hyperplasias caused by human papillomavirus (HPV) that can clinically mimic SKs but differ in that they most frequently occur in younger individuals.

• Verrucae present as rough papules with pinpoint red or black dots and favor acral locations, whereas condylomata acuminata occur in the anogenital region.

• SKs can also have superimposed warts, which may present with overlying features as previously described or with filiform (finger like) projections.
• Differentiation between an irritated SK, an SCC in situ (known as Bowen disease), and SCC can be quite difficult and may require biopsy and histopathologic examination, but there should be no evidence of involvement of the dermis in irritated SKs.
• The keratotic plugging, stuck-on appearance, and/or overlying scale are helpful features in distinguishing SKs from melanocytic neoplasms, but they can still be extremely difficult to distinguish, so biopsy can be performed in any cases of uncertainty.
• Acrochordons have a pedunculated shape and are usually smoother and smaller in size than SKs.
• Tumor of the follicular infundibulum is a benign adnexal tumor that is distinguished from an SK by a biopsy.

Work-up

• SKs can usually be easily recognized clinically, but lesions that are difficult to diagnose by inspection alone can be biopsied.

• Biopsy may be necessary if there is a history of recent change or inflammation or it is a larger dark lesion that causes concern for melanoma.

• If biopsy is warranted, shave biopsy is recommended.

• The specimen should be sent to a dermatopathologist experienced in interpreting keratinocytic lesions, given the difficulty of differentiating irritated/inflamed SK from SCC in situ.

Initial steps in management

• Treatment of SKs is not necessary because they are harmless; however, they may be removed if they are symptomatic or cosmetically bothersome.
• Treatment options include cryosurgery, curettage, or shave removal.
• Because SKs are superficial lesions, their removal causes minimal scarring, but the skin may be lighter than the surrounding area; this may fade with time or stay permanently.

Warning signs/common pitfalls

• There are many entities that may have similar appearance to SKs, and therefore a malignancy can be misdiagnosed as an SK. Lesions should be biopsied if there is any concern for the possibility of malignancy.
• It is worth noting that there are instances where malignant neoplasms arise within or adjacent to SKs, but this is likely coincidental and because of the prevalence of both in the population at large.
• Sudden appearance of multiple SKs lesions may be associated with internal malignancy (the so-called “sign of Leser-Trélat”); however, the existence of this association is controversial.

Counseling

You have seborrheic keratoses, which are very common benign skin lesions. They are seen in nearly all older individuals. You will likely continue to develop more throughout your lifetime and there is no way to prevent this, but they are not contagious or dangerous. The cause of seborrheic keratoses is unknown, but they seem to run in families and studies suggest that sun exposure may play a role.

Seborrheic keratoses are usually asymptomatic; however, they can become itchy and inflamed, and catch on clothing. If your lesions become symptomatic or you would like them removed for cosmetic reasons, there are options available. The most common option is cryosurgery, which involves freezing the lesion with liquid nitrogen. They can also be removed under local anesthesia by scraping the lesion from the skin or cutting it off with a small, flat blade. Their removal should cause minimal scarring, but the skin may be lighter than the surrounding area; this can either fade with time or stay permanently.

If you notice any changes in your lesions or a sudden increase in their number, you should make an appointment with a dermatologist so they can be reexamined.

Acquired digital fibrokeratoma

Erisa Alia and Philip E. Kerr

Clinical features

Acquired digital fibrokeratoma (ADFK) is a relatively rare, benign, fibroepithelial tumor with a predilection for the fingers and toes. Occasionally, it can be found on the dorsum of the hand, elbow, prepatellar area, nail bed, and heel. ADFK presents as small, firm, solitary, skin-colored to pink, exophytic papulonodules. Its surface is hyperkeratotic, and it is surrounded by a characteristic collarette of slightly raised skin at its base. ADFK is usually asymptomatic.

It has a tendency to gradually increase in size and occurs more often in middle-aged adults. The etiology remains unknown; however, trauma to the site may be contributory.

Differential diagnosis

ADFK is most commonly diagnosed based on history and physical examination. Nevertheless, to predict the response to treatment, it is important to differentiate ADFK from other cutaneous lesions in the differential diagnosis. These include verruca vulgaris (the common wart), supernumerary digits, periungual/subungual fibroma, and pyogenic granuloma (PG).

• ADFK’s classic location on the lateral aspect of digits and its characteristic collarette of scale help distinguish ADFK from verruca vulgaris. Verrucae are also often tender or painful and demonstrate loss of surface dermatoglyphics. If magnified, multiple black or red dots can be easily appreciated. Biopsy of verruca is diagnostic and shows parakeratosis, papillomatosis, and koilocytes.
• A supernumerary digit is present at birth and usually located on the medial side of the fifth digit. Biopsy reveals nerve bundles in the dermis.
• With periungual/subungual fibroma, location is the distinguishing feature. Fibromas emanate near the proximal and lateral nail folds, whereas ADFK typically does not occur near the nail unit (although a periungual/subungual variant of ADFK exists, in which case histopathologic examination is required for diagnosis).
• Although location may be similar between PG and ADFK, they are unlikely to be confused with one another because PGs are vascular tumors that bleed profusely, whereas ADFKs are asymptomatic and do not appear vascular.