1. What are the primary lesions that you would expect to find in keratoacanthoma?

31 Keratoacanthoma (Molluscum Sebaceum)

CLINICAL APPLICATION QUESTIONS

A 35-year-old farmer is seen at your office for a rapidly growing nodule on his right upper lip near the vermilion margin. This was first noticed 4 weeks ago. He is concerned about the character and potential of this lesion. Physical examination of the involved region reveals a lesion suggesting a keratoacanthoma (KA).

1. What are the primary lesions that you would expect to find in keratoacanthoma?

2. What are the secondary lesions that you would expect to find in keratoacanthoma?

3. Keratoacanthoma is most commonly mistaken for what other condition?

4. What should you tell the patient about keratoacanthoma?

5. Should you treat keratoacanthoma in this patient, and if so, how?

APPLICATION GUIDELINES Specific History

Onset

KAs are common tumors that are first encountered in middle-aged patients and are frequently seen from age 60 onward. Onset is usually sudden, with rapid growth, and most patients give definite timing regarding the onset and progression.

Evolution of Disease Process

A typical KA begins as a solitary firm papule on sun-damaged but otherwise normal skin. Early lesions may resemble a molluscum wart or a verrucous wart; however, rapid growth and large size usually offer a clue as to the true nature of the tumor. A typical KA measures 1 to 2 cm across at the base, and is elevated 0.5 to 1.0 cm above the adjacent skin surface.

The initial rapid growth phase lasts 1 to 2 months, and the lesions then typically become stable in size. This stationary phase may last from a few to several months, and is the stage during which patients most often present for evaluation. After a period of sta- bility, and frequently after biopsy, some KAs will enter a regressive phase, which may last for 6 months. Following spontaneous regression, there is almost always some residual scarring at the site, which consists of a depression with papules and elevated tags at the margin. Recurrence after spontaneous resolution has been reported.

Special forms of keratoacanthoma include (1) a generalized eruptive type, (2) a mul- tiple type (following cutaneous carcinogen exposure), (3) a giant type (up to 15 cm in

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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

diameter), and (4) a dominantly inherited self-healing variant. There is disagreement over the precise classification of this variant.

Evolution of Skin Lesions

See Evolution of Disease Process section, above.

Provoking Factors

Because of the preference of keratoacanthoma for sun-exposed skin, and because KAs are seen most often in persons with severe solar damage, there is no question that UV radi- ation is a major factor in their etiology. As a corollary, fair-skinned Caucasians who sun- burn readily and are subject to solar injury are the persons who present with these tumors most frequently.

Occurrence of a KA shortly after penetrating, but minor, physical trauma to the site is common. Other provoking factors include topical carcinogens (such as tar compounds) and natural or iatrogenic states of immunologic suppression.

Self-Medication

Self-treatment is not a problem.

Supplemental Review From General History

The occurrence of giant, atypical, or multiple KAs is an indication for review of fam- ily history, possible chemical carcinogen exposure, and any factors or concomitant condi- tions that might cause general immune suppression.

Dermatologic Physical Exam Primary Lesions

1. A rapidly growing dome-shaped papule with a central dull pebbly core (see Photo 40).

2. A rapidly growing dome-shaped nodule with a central dull pebbly core (see Photos 41,42).

The initial lesion is a papule with a central depression or dell. The peripheral epithe- lial lip can vary from flesh-colored to pink or orange-red depending on the degree of inflammatory reaction and the number of dilated (telangiectatic) vessels. There is no infil- tration of the skin peripheral to the margins of the lesion. The central cavity develops as the KA matures, and becomes increasingly larger as the epithelial rim thins. The central keratotic material has a gray-yellow color. In the early papule/nodule stage with the dell there can be considerable resemblance to a basal cell carcinoma. Small lesions with an early keratotic core can simulate a large molluscum wart.

Secondary Lesions

1. Giant lesions form a rough, pebbly central vegetation. The epithelial margin may become quite diminutive and difficult to recognize.

2. Scarring with a depression and peripheral epidermal tags are usually left after

spontaneous regression (see Photo 43).

Distribution

Microdistribution: Some keratoacanthomas develop from the upper epithelium of the hair follicle; however, this distribution is not clinically evident.

Macrodistribution: 90% of KAs occur on the sun-exposed skin of the face, hands, and forearms. They can also occur on covered sites and have been reported on the ver- milion margin of the lip, the buccal mucosa, in the anogenital regions, and beneath nails (see Fig. 9).

Configuration

Grouped in the case of multiple KAs.

Figure 9: Macrodistribution of keratoacanthomas.

Indicated Supporting Diagnostic Data Biopsy

The histology of a keratoacanthoma is very similar to that of a well-differentiated squamous cell carcinoma of the skin. KAs commonly contain squamous cells with atypi- cal mitosis, individual cell keratinization, and other histologic signs of malignancy. The microscopic differentiation is dependent on both the cellular detail and the low-power configuration of the lesion. At each margin, a narrow spur of dermal connective tissue sep- arates the normal epidermis from the lesion at the transitional junction between the nor- mal and proliferating cells. For this reason, marginal punch biopsy is not adequate to distinguish between the two. Excisional biopsy or an incisional biopsy that contains a cross-section of the lesion into the adjacent normal skin is needed.

Therapy Surgery

Because keratoacanthomas are difficult to separate clinically and microscopically from squamous cell carcinoma, and since substantial scarring occurs after spontaneous involution, small- to moderate-sized lesions are usually removed by excisional surgery.

Giant lesions, or those in locations where removal would be mutilating or require exten- sive reconstruction, should be referred to a dermatologic consultant for consideration of alternative treatment. Recurrences of keratoacanthoma can occur after any type of therapy, and after apparent spontaneous involution.

Alternative Therapy

Other modalities used in the destruction of KAs include curettage and electrodesicca- tion, cryosurgery, intralesional injections of triamcinolone or 5-FU, highly fractionated soft X-irradiation, and the use of oral retinoids for multiple lesions.

Conditions That May Simulate Keratoacanthomas Molluscum Contagiosum

An early KA lesion with a keratotic core may resemble a giant molluscum wart. The solitary lesion, rapid growth, and ultimate size will usually serve to distinguish the two.

Basal Cell Carcinoma

Early KA lesions with a central dell, a flesh-colored margin, and prominent vessels can be confused with a BCC. Basal cells are slow-growing, however, and are distinguish- able as the central keratin core of the KA develops.

Squamous Cell Carcinoma

Both tumors can develop rapidly and show great clinical and microscopic similarities.

They must be distinguished microscopically; however, this is not always possible.

Other Vegetating Lesions

Some deep fungal diseases produce vegetating lesions that could be confused with a giant

highly keratotic KA. A punch biopsy with appropriate special stains should distinguish the two.

ANSWERS TO CLINICAL APPLICATION QUESTIONS History Review

A 35-year-old farmer is seen at your office for a rapidly growing nodule on his right upper lip near the vermilion margin. This was first noticed 4 weeks ago. He is concerned about the character and potential of this lesion. Physical examination of the involved region reveals a lesion suggesting a keratoacanthoma.

1. What are the primary lesions that you would expect to find in keratoa- canthoma?

Answer: A rapidly growing dome-shaped papule or nodule with a central dull pebbly core.

2. What are the secondary lesions that you would expect to find in keratoa- canthoma?

Answer: Central vegetation and/or scarring.

3. Keratoacanthoma is most commonly mistaken for what other condition?

Answer: Squamous cell carcinoma resembles keratoacanthoma both on physical examination and microscopic evaluation. Distinguishing the two is not always possible.

4. What should you tell the patient about keratoacanthoma?

Answer: Keratoacanthoma is classified as a benign lesion but shows many signs and microscopic features of malignancy. Although true keratoacanthomas do not metastasize, they can cause significant scarring and alteration when they occur on a cosmetically sensitive site. Treatment is recommended to minimize scarring and to distinguish keratoacanthoma from squamous cell carcinoma.

5. Should you treat keratoacanthoma in this patient, and if so, how?

Answer: When a keratoacanthoma is small or occurs in an area that is not cos-

metically sensitive, conservative elliptical excision or saucerization followed by

curettage and desiccation is acceptable treatment. Giant keratoacanthomas or

lesions on cosmetically sensitive areas such as the face should be referred to a der-

matologic consultant for consideration of alternative treatments.