25 Seborrheic Keratosis

25 Seborrheic Keratosis (Old Age Spots, Liver Spots)

CLINICAL APPLICATION QUESTIONS

A 70-year-old man is seen at your office for multiple raised pigmented lesions over his back and chest. These have developed gradually over several years. There are two lesions on the mid-lower back that intermittently itch intensely and are somewhat larger and much darker than the other lesions, which number 50 or more. Physical examina- tion of the entire region reveals multiple seborrheic keratoses. Except for the two lesions in question there are no other suspect lesions. The patient is very worried about melanoma.

1. Should the two darker lesions be biopsied for melanoma?

2. If you determine that one or both of the darker lesions are seborrheic keratoses, what should you tell the patient about them?

3. What are the primary lesions that you would expect to find with seborrheic ker- atoses?

4. What are the secondary lesions that you would expect to find with seborrheic ker- atoses?

5. If you determine that one or both of the darker lesions are seborrheic keratoses, how should you treat them?

APPLICATION GUIDELINES Specific History

Onset

These very common benign lesions normally begin insidiously during early or mid- middle age. This gradual onset is very typical. The sudden onset of multiple rapidly grow- ing seborrheic keratuses (SKs) associated with pruritus is known as the sign of Leser-Trélat, and may indicate an underlying visceral malignancy, a leukemia, or lym- phoma.

Evolution of Disease Process and Skin Lesions

Seborrheic keratoses are most often evident during the fifth decade, but may be pres- ent as early as the third decade. They begin as flat, tan, superficial 1- to 3-mm papules with a dull surface, and in their early stages may be very difficult to distinguish from flat warts.

Over many years, certain lesions increase in size and thickness, then become increasingly keratotic, but retain their superficial character. SKs are described as appearing to have been

“pasted” or “stuck on” normal-appearing skin (see Photo 1). Common coloration is gray- tan, yellow-tan, pink-tan, or medium brown. Color can vary from grey-white to black.

235

From: Current Clinical Practice: Dermatology Skills for Primary Care: An Illustrated Guide D.J. Trozak, D.J. Tennenhouse, and J.J. Russell © Humana Press, Totowa, NJ

236 Part V / Malignant Skin Diseases Crypts of keratotic debris sometimes cause the formation of comedones (plugs) over their surface. Developed lesions have an uneven surface and a soft, waxy character when pal- pated. Average size of developed lesions is 1 to 2 cm; however, some lesions may reach sev- eral centimeters, especially on the temple and scalp regions. Around the neck and on the eyelids they are often pedunculated (see Photo 10). While certain lesions grow and thicken, others may disappear after trauma or episodes of inflammation. The general trend is for the lesions to become larger, thicker, and more noticeable with advancing age. Rare reports in the dermatology literature document the combined presence of an SK with a common basal or squamous cell carcinoma. SKs are so common and these reports are so infrequent that it would seem best to consider these as the coincidental occurrence of two lesions at the same site. SKs are considered benign without significant risk of malignant degeneration.

Provoking Factors

SKs appear to be a dominantly inherited trait with marked variation in genetic pene- trance. Occasionally, patients present with lesions strikingly limited to sun-exposed skin, raising the possibility of ultraviolet light being a provoking factor. Many patients, how- ever, have lesions only on covered regions, and no proven provoking factors have been identified.

Self-Medication

Self-treatment is not a problem.

Supplemental Review From General History

Sudden development of large numbers of rapidly growing seborrheic keratoses, espe- cially when associated with itching (Leser-Trélat sign), is an indication for an in-depth history and physical exam.

Dermatologic Physical Exam Primary Lesions

1. Dull 1- to 3-mm papules (see Photo 1).

2. Keratotic “stuck on” plaques 0.5 to 2 cm (see Photo 2), occasionally larger (see Photo 3)

Secondary Lesions Usually none.

Distribution

Microdistribution: None.

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).

Configuration

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 Biopsy

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.

Therapy

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

Figure 1: Macrodistribution of seborrheic keratosis.

238 Part V / Malignant Skin Diseases very unusual circumstances, surgical excision of these lesions is inappropriate treatment.

When the clinical diagnosis is uncertain, referral to a dermatologist is necessary and usu- ally cost-effective.

Cryosurgery

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 advan- tage of this technique is the absence of scarring. Heavily pigmented persons must be warned about the possibility of posttreatment hyper- or hypopigmentation. This is espe- cially 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 appro- priate 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.

Chemical Removal

Removal of SKs can also be accomplished with trichloroacetic acid or concentrated preparations of various α-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 Planar Warts

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.

Solar Lentigo

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 (LN

).

Actinic Keratosis and Squamous Cell Carcinoma

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.

ANSWERS TO CLINICAL APPLICATION QUESTIONS History Review

A 70-year-old man is seen at your office for multiple raised pigmented lesions over his back and chest. These have developed gradually over several years. There are two lesions on the mid-lower back that intermittently itch intensely and are somewhat larger and much darker than the other lesions, which number 50 or more. Physical examina- tion of the entire region reveals multiple seborrheic keratoses. Except for the two lesions in question there are no other suspect lesions. The patient is very worried about melanoma.

1. Should the two darker lesions be biopsied for melanoma?

Answer: Despite its darker color, if the lesion has a waxy keratotic surface and a typical “stuck-on” appearance, it is clinically consistent with a benign SK. The lesion should not be biopsied at this time. If you strongly suspect the lesion is an SK but are uncertain that it has a superficial “stuck-on” character or that its sur- face is not waxy and keratotic, either obtain a dermatologic consultation or per- form a punch biopsy for the purpose of identification.

2. If you determine that one or both of the darker lesions are seborrheic keratoses, what should you tell the patient about them?

Answer: Seborrheic keratoses are benign lesions. Treatment is optional. If spe- cific lesions are sufficiently symptomatic that removal is desired, the appropriate approach is cryotherapy, which is almost always successful.

3. What are the primary lesions that you would expect to find with sebor- rheic keratoses?

Answer: Dull 1- to 3-mm papules, and waxy keratotic “stuck-on” appearing plaques that are 0.5 to 2 cm in size but occasionally larger. Color may vary from gray-white to black.

4. What are the secondary lesions that you would expect to find with sebor- rheic keratoses?

Answer: Usually none.

240 Part V / Malignant Skin Diseases 5. If you determine that one or both of the darker lesions are seborrheic keratoses, how should you treat them?

Answer: Cryotherapy is appropriate, with immediate follow-up if the lesions

have not resolved in 30 days.