Macrodistribution: SKs are seen primarily on the face, upper back, and central chest. They can occur at almost any site. Only the palms, soles, and mucous membranes are spared (see Fig. 1).
Occasionally SKs will follow lines of cleavage (see Photo 2). This may produce a "Christmas tree" pattern. Generally they are randomly distributed.
Indicated Supporting Diagnostic Data
The vast majority of SKs can be diagnosed by physical inspection. Depending on their stage of evolution, there are times when SKs may be difficult to distinguish clinically from a pigmented basal cell carcinoma, lentigo maligna, or a malignant melanoma. In these rare instances the lesion should be referred to a dermatologist for evaluation and a decision regarding the appropriate type of biopsy if one is indicated.
Seborrheic keratoses are benign lesions and treatment is elective. Exceptions include instances where they are symptomatic because of location, due to inflammation, or after trauma. These benign growths can be treated by nonscarring techniques. Except under very unusual circumstances, surgical excision of these lesions is inappropriate treatment. When the clinical diagnosis is uncertain, referral to a dermatologist is necessary and usually cost-effective.
Light applications of liquid nitrogen sufficient to produce a 0.5- to 1-mm rim of freeze at the perimeter of the base of the SK is usually sufficient for total removal. The advantage of this technique is the absence of scarring. Heavily pigmented persons must be warned about the possibility of posttreatment hyper- or hypopigmentation. This is especially important when working on the facial area. When patients express concern in this regard, we encourage treatment of one or two test lesions in an inconspicuous location before proceeding. During the sunny season, we strongly urge sun avoidance and the use of a sunscreen with makeup to prevent posttreatment darkening. Cryosurgery is the appropriate way to treat these lesions.
Shave Excision With Light Curettage and Electrodesiccation
On rare occasions one encounters an SK that simply will not respond to cryotherapy. When this occurs, the lesion must be biopsied to be certain it is not a more aggressive type of pigmented lesion. Once the lesion is found to be benign, therapy should consist of shave excision and gentle curettage followed by electrodesiccation at a very low setting. This procedure almost always leaves some superficial scarring and permanent pigment loss, and the patient should be forewarned.
Removal of SKs can also be accomplished with trichloroacetic acid or concentrated preparations of various a-hydroxy acids. Chemical removal usually also involves some use of curettage or combined use of liquid nitrogen, and should be performed only by a skilled operator.
Conditions That May Simulate Seborrheic Keratosis
Early SKs on the dorsal forearms and hands can be virtually indistinguishable from planar warts except on biopsy. Generally, planar warts present in children or young adults, and tend to group asymmetrically in certain locations. SKs usually occur a decade or more later and are typically symmetrical.
Differentiation between an early facial SK and a chronic solar lentigo can be difficult clinically. Usually with careful examination the raised edge of the SK is evident, whereas the lentigo is macular. Biopsy will distinguish them but is rarely relevant since both are benign lesions and both respond to liquid nitrogen (LN2).
Usually SKs can be distinguished from premalignant sun-induced actinic keratoses (AKs) by their thicker "stuck-on" appearance and waxy surface feel. AKs may be brown in color, but there is usually a surface scale, a background of erythema, and the surface is rough and abrasive to the touch. Squamous cell carcinomas often have a keratotic surface, but unlike the SK they have an indurated base.
Malignant Melanoma and Pigmented Basal Cell Carcinoma
Usually the stuck-on appearance and waxy surface will serve to distinguish SKs. When there is doubt as to the diagnosis, referral to a dermatologist is indicated. This may avoid a needless scar, or prevent inappropriate handling of a potentially dangerous growth. If biopsy or excision is indicated, someone fully conversant with pigmented tumors should make that decision.
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