SEBORRHEIC KERATOSIS
One
of the most commonly encountered of all benign skin growths is the seborrheic
keratosis. These growths come in all sizes and shapes and invariably can be
found on any human older than 40 years of age. They commonly begin in the
fourth decade of life and tend to increase in number over one’s lifetime. They
have no malignant potential but are often brought to the attention of
physicians because they can mimic other skin growths, most importantly
malignant melanoma.
Clinical Findings: Seborrheic keratoses are found equally in males
and females, and they are seen in all races. They begin to manifest in the
third to fifth decade of life and continue to increase in number there-after.
They come in various sizes and shapes. Some are quite small, whereas others can
be 5 to 6 cm in diameter. They occur almost exclusively in sun-exposed regions
of the body. The classic description is that of a 1- to 2-cm plaque with a
“stuck-on” appearance and small horn cysts. Most commonly flesh colored, they
can also be tan, brown, or almost black. It is for this reason that they are
occasionally mistaken for melanoma. Most individuals have a few scattered
keratoses, but not infrequently a patient has thousands of these skin growths.
Many clinical variants of seborrheic
keratosis can be seen. Stucco keratoses are small (1-5 mm), graytan papules
with a stuck-on appearance or thin patches on the lower extremities. Dermatosis
papulosis is a condition in which multiple seborrheic keratoses occur on the
face and neck. This condition has a definite inheritance pattern.
Some seborrheic keratoses are smooth
surfaced, but more commonly they have a pebbly or dry, rough surface. They have
a characteristic stuck-on appearance, and in some instances they are easily
removed by gently peeling from one side. These growths can easily become
irritated or inflamed. The resulting pain, itching, or bleeding often brings
the patient to medical treatment.
The sign of Leser-Trélat is the rapid
onset of multiple seborrheic keratoses associated with an underlying internal
malignancy. This sign has not been validated and is not a reliable indicator of
an internal malignancy.
Histology: There is a well-circumscribed proliferation of
keratinocytes. They have an exophytic growth pattern. The keratinocytes show
acanthosis and hyperkeratosis. Marked papillomatosis is also commonly
encountered. Two types of cysts are seen within the seborrheic keratosis. The
horn cyst develops within the epidermis and is made of a keratin-filled cystic
space with a surrounding granular cell layer. A pseudo-horn cyst is formed by
an invagination of the stratum corneum into the underlying epidermis. Multiple
histological subtypes have been described.
Pathogenesis: The formation of this benign epidermal tumor is
not fully understood. It is caused by a proliferation of keratinocytes within
the epidermis. The location in sun-exposed skin and the increasing number of
lesions with increasing age has led some to believe that they are caused by a
local suppression of the immune system that results in the epidermal
proliferations. A definitive inheritance pattern has not been discovered, but
these keratoses show some genetic predisposition. Chromosomal analysis of these
tumors has not revealed any chromosomal defects. A link with the human
papillomavirus has been proposed but has yet to be proven.
Treatment: These keratoses require no therapy. If they become
inflamed or irritated, a simple shave biopsy removal is curative. Cryotherapy
and curettage are often used to treat these benign skin growths, and both are
extremely effective. After cryotherapy treatment, a blister usually forms at
the base of the seborrheic keratosis, and within a day or two the keratosis
falls off.
Another extremely effective method of
removal that can be done in the office is cryotherapy followed by a light
curettage; this also allows for histological evaluation. Occasionally, dark
brown or black seborrheic keratoses can mimic melanoma, and in other cases a
melanoma may arise adjacent to a seborrheic keratosis and mislead the
clinician. If there is ever a doubt that the growth could be a melanoma, a
biopsy is required. Thi allows for pathological confirmation of the diagnosis.
