Seborrheic keratosis is a benign, noninvasive round to ovoid (or oval), variably raised, light to darker brown to sometimes black, sharply demarcated papule or plaque that varies in diameter from a few millimeters to several centimeters.
Clinical Manifestation
Clinically, seborrheic keratoses begin as small, multiple, round or oval, raised, flesh-colored, yellow, or tan, papules that slowly grow and eventually turn dark brown to black, greasy, verrucous lesions with a distinct border.
The keratoses have a scaly surface and appear to be stuck or pasted on the skin (see Figure X-1); and the surface often shows pronounced keratotic plugging.
The rough scale may sometimes flake or be rubbed off but will always regrow. Seborrheic keratoses are benign and generally asymptomatic. However, irritated lesions or those in intertriginous areas Opens in new window may cause mild itching..
Seborrheic keratoses are more often seen in persons over 40 years. The most commonly affected areas are the face, neck trunk, and extremities that have been chronically exposed to sunlight.
A variant of seborreic keratoses known as dermatosis papulosa nigra Opens in new window is seen primarily on the cheeks in blacks or other dark skinned individuals with a familial predisposition.
Seborrheic keratosis from the genital region may contain human papillomavirus deoxyribonucleic acid (DNA). In mature seborrheic keratoses, DNA synthesis is decreased, whereas ribonucleic acid (RNA) and protein synthesis are increased.
Assessment
Lesions of seborrheic keratosis typically have two colors and irregular border, similar to the characteristics of malignant melanoma. They are composed predominantly of proliferating keratinocytes (epidermal cells) and are not primarily melanocytic in orgin.
Any doubts concerning the exact diagnosis of the keratosis may be resolved by pathologic examination of a small punch biopsy, shave biopsy, or curettage specimen.
The base of all cutaneous horns should be submitted for histologic diagnosis. Shave biopsies or curettage specimens are often not sufficient for definitive histologic diagnosis.
A genetic (polygenic) predisposition exists to develop seborrheic keratoses.
Some have attributed the development of multiple seborrheic keratoses to estrogen therapy, preexisting inflammatory dermatoses, acromegaly, and various internal malignancies.
The latter association (Leser-Trélat sign), although somewhat controversial, should at least arouse one’s suspicion when multiple pruritic seborrheic keratoses arise rapidly from previously normal skin.
Therapeutics
Treatment is usually unnecessary. Concern about these lesions is primarily cosmetic; occasionally, they may cause anxiety because their dark color raises the question of melanoma.
Rarely, malignant lesions (i.e., Bowen’s disease) can arise from seborrheic keratoses, especially the reticulated type on sun-damaged skin. Therapy then should therefore be as simple, rapid, and cosmetically acceptable as possible.
After treatment, a small area of hypopigmentation may be left at the site of the keratosis. If there is any doubt regarding diagnosis, especially in darkly pigmented individuals, a biopsy should be performed.
Application of liquid nitrogen (15 to 20 seconds) will result in removal of lesions without a subsequent cicatrix and is generally the simplest method. Multiple areas can be treated easily without anesthesia.
Simple curettage, with or without anesthesia, leaves an excellent cosmetic result. Lesions lightly frozen with a refrigerant, CO2, or liquid nitrogen may sometimes be scraped off more easily.
Monsel’s solution (ferric subsulfate), ferric chloride, aluminium chloride, Gelfoam, weak acids (30% trichloroacetic), or pressure may be used for hemostasis.
Light electrodesiccation will accomplish the same end but may induce a small scar. Lesions should remain uncovered or have only a light, nonocclusive dressing.
Very thick seborrheic keratoses may be best removed with a superficial shave excision.
Lesions of dermatosis papulsa nigra are best treated by simple curettage but may also be treated by Gradle scissor excision, light electrosurgery, laser surgery, or cryosurgery; it is particularly important not to treat too aggressively so as to avoid posttreatment hypopigmentation.
Ammonium lactate 12% lotion (Lac-Hydrin) applied b.i.d. for 1 to 2 months may reduce the height of seborrheic keratoses but will not change the length or color of the lesions.
Figure X-1 | Photo courtesy of Academic Dermatology of Nevada Opens in new window
