Seborrheic Keratosis

A seborrheic keratosis (SK) is an extremely common benign skin growth that becomes apparent in people older than 40 years of age. They are the most common neoplasm in the elderly and have virtually no malignant potential.
The use of the word “seborrheic,” a misnomer, stems from the occasional “greasy” or shiny appearance of the lesions; SKs are actually epidermal in origin, with no sebaceous derivation.
Patients often report a positive family history of SKs; men and women are equally affected.
SKs have been whimsically described as “barnacles in the sea of life” and “maturity spots”; these metaphors are intended to allay patients' anxieties.

SKs are generally asymptomatic; however, they may itch when irritated or inflamed.
At times, they are cosmetically undesirable to the patient.
The typical SK has a warty, “stuck-on” appearance that ranges from tan to dark brown to black.
The appearance of individual lesions tends to vary considerably, even on the same patient.
Lesions may be warty and tortoiseshell-like (Fig. 30.12); scaly, flat, or almost flat (Fig. 30.13); or small pigmented papules similar to skin tags (discussed below) (Fig. 30.14).
Often the “dry,” crumbly, keratotic surface of some lesions are sometimes rubbed or picked off, only to recur later.
To the untrained eye, as well as to dermatologists, SKs can resemble melanomas since they may share similar features (i.e., they may be asymmetric, have irregular or notched borders, and vary in color [see Chapter 31: Premalignant and Malignant Cutaneous Neoplasms]).

Stucco Keratoses

Stucco keratoses are a nonpigmented variant of SK most often seen in the elderly.
Stucco keratoses are skin-colored or whitish papules that become whiter and scalier when they are scratched. They typify the “dry, stuck-on” type of seborrheic keratosis.
They are commonly found on the distal lower leg, particularly around the ankles (Fig. 30.17), less likely on the dorsal forearms.

Dermatosis Papulosa Nigra

This common manifestation is diagnosed primarily in African-American, Afro-Caribbean, and sub-Saharan African blacks; however, it is also seen in darker-skinned persons of other races. Lesions start appearing in adolescence and increase in number as persons age.
Dermatosis papulosa nigra (DPN) lesions are histopathologically identical to SKs and are considered to be of autosomal dominant inheritance.
Lesions are darkly pigmented and, in contrast to typical SKs, they have minimal, if any, scale.
DPNs generally appear on the face, especially the upper cheeks and lateral orbital areas (Fig. 30.18).

Sign of Leser-Trélat

A condition that refers to the sudden appearance of multiple SKs in a short period or a rapid increase in their size.
It is a rare phenomenon and is presumed by some observers to be a cutaneous sign of leukemia or internal malignant disease, especially of the gastrointestinal tract, prostate, breast, ovary, uterus, liver, or lung.
However, in light of the frequency of malignant disease in the elderly, and the ubiquitous presence of SKs in this age group, the relationship is believed by some observers to be fortuitous.

Outline
Stucco Keratoses
Dermatosis Papulosa Nigra
Sign of Leser-Trélat

With experience, SKs are easily recognized.
If necessary, a shave biopsy (using a no. 15 scalpel blade) or curettage may be performed for histologic confirmation (see Chapter 35: Diagnostic and Therapeutic Techniques).

Differential Diagnosis

Verruca Vulgaris (see Chapter 18: Superficial Fungal Infections)

Solar Lentigo (see above)

Melanocytic Nevus/Dysplastic Nevus (see earlier Discussion)

Points to Remember

SKs are mainly a cosmetic concern, except when they are inflamed or irritated and can be an annoyance. The challenge for primary care clinicians is to distinguish these lesions from skin cancer, particularly malignant melanoma.
Lesions may be quite numerous on some persons. Because SKs may, at times, be confused with melanoma, careful visual examination of all lesions should be performed.

Management

Patients with SKs are often referred to dermatologists with a presumptive diagnosis of warts or moles or to have these lesions evaluated to rule out cancer, particularly melanoma.
Learning to recognize SKs should obviate the need for many of these referrals. When a patient is referred, a biopsy (generally a shave biopsy) is performed if necessary to confirm the diagnosis or to distinguish SK from a pigmented basal cell carcinoma, melanocytic nevus, wart, or melanoma.
Because some patients have numerous lesions, it is an impractical expenditure of time and money to perform multiple biopsies of lesions, as long as the clinical appearance is typical.
An excisional biopsy should always be performed whenever malignant melanoma is suspected.

Treatment

Cryosurgery is performed with liquid nitrogen spray, cotton swab application, or light electrocautery and curettage (treating the base of the lesion helps to prevent recurrence).
Excisional surgery, which results in scar formation, is unnecessary, unless the clinical appearance is suggestive of a malignant disease such as melanoma.

Helpful Hint

SKs present in many shapes, colors, and sizes. It is a good idea to become familiar with these lesions by consistently examining the skin of all adult patients.

Distribution of Lesions

SKs most often are located on the back, chest, and face, particularly along the frontal hairline (Fig. 30.15) and scalp. They are also frequently found on the arms, legs, and abdomen (Fig. 30.16).
Smaller lesions similar to skin tags can be seen around the neck, under the breast, or in the axillae.
In women, lesions are often seen under and between the breasts.
When many lesions are present, the distribution is usually bilateral and symmetric.