An Overview of Seborrheic Keratosis

Seborrheic keratosis, also known as seborrheic verruca or "skin barnacles," are benign skin tumors that can look disconcertingly like melanoma. Similar in characteristics to liver spots (senile lentigo), seborrheic keratosis develops in a type of skin cell known as a keratinocyte, which is on the outermost layer of skin (epidermis). The tumors can vary by location, size, and appearance, but are typically light tan to dark brown in color.

While most dermatologists are able to diagnose seborrheic keratosis by appearance alone, any abnormality may require a skin biopsy to ensure that cancer is not involved. Seborrheic keratoses can become inflamed or irritated, so treatment is sometimes considered for these reasons, as well as for aesthetic purposes.

The cause of seborrheic keratosis is unknown but is believed to have a genetic component as it tends to run in families. While sun exposure may darken a lesion, the condition should not be confused with freckles, solar keratosis (sun spots), or melasma (a condition in which sun exposure can give rise dark patches, especially in women).

Seborrheic keratosis is characterized by benign tumors referred to as lesions. The lesions may rest flat against the skin or be slightly raised. They tend to develop in groups and can sometimes pepper an entire area of skin (such as the back). The lesions may be round, oval, or irregularly shaped and range in size from a pinpoint to over an inch in diameter. Seborrheic keratosis is most commonly seen in older people.

Because only the top skin layer is involved, raised lesions often have a "pasted-on" appearance similar to a barnacle.

Smooth lesions often contain seed-like bumps that may be lighter or darker than the surrounding skin. The bumps, referred to as horn pearls, are simply keratinocytes that have died, consolidated, and formed horny spurs.

Seborrheic keratoses are not painful but tend to itch as you get older. If scratched or picked at, a lesion can become red and start to bleed.

Rarely does seborrheic keratosis become cancerous. If it does, it will most likely develop into basal cell carcinoma (BCC), the type that accounts for eight of every 10 skin cancers in America. BCC tumors tend to develop in sun-exposed parts of the body and grow very slowly. Unlike melanoma, BCC does not typically metastasize (spread to other parts of the body).

BCC can co-exist with seborrheic keratosis, so it is sometimes difficult to know if the keratotic lesion turned malignant or the cancer developed on its own.

Less commonly, squamous cell carcinoma (SCC) may arise from a keratotic lesion. SCC also tends to develop in sun-exposed areas but, unlike BCC, is more likely to move into deeper cells and metastasize. Some studies have suggested that immune suppression is likely linked to the development of SCC in people with seborrheic keratosis.

A dermatologist can usually diagnose seborrheic keratosis with either the naked eye or a lighted instrument known as a dermatoscope.

Despite our lack of understanding about the condition, variants of the lesions can be characterized based on their location and appearance:

• Common seborrheic keratosis involves basal cells situated in the innermost layer of the epidermis.
• Dermatosis papulosa nigra typically affects dark-skinned people, causing dark spots on the face.
• Inverted follicular keratosis is characterized by white or pinkish lesions.
• Reticular seborrheic keratosis involves multiple layers of basal cells and tends to be raised without horn pearls.
• Stucco keratosis usually appears as small dots on the shins, ankles, or feet.

If a lesion looks suspicious, the doctor may want to perform a biopsy to rule out skin cancer.

This may involve either a shave biopsy (in which the lesion is shaved to remove a tissue sample), a punch biopsy (where a hole-punch-type device removes a narrow cylinder of tissue), or an excisional biopsy (using a scalpel and sutures). Lab results are usually returned within one to two weeks.

If cancer is found, additional tests would be ordered to see if the malignancy has affected nearby lymph nodes or has spread to distant organs.

Seborrheic keratosis is typically not treated. If it is, it is either because a patient considers the lesion aesthetically undesirable, it is being irritated by clothing or jewelry, or is subject to bleeding or infection (usually because it is being scratched or picked at).

Among the treatment options:

• Electrocautery, in which tissue is burned with an electrical current, is a standard means of removing small benign lesions. The procedure typically requires a local anesthetic or numbing agent. Once the lesion is removed, it can take two to four weeks for the scab to fall off and the underlying tissue to heal.
• Liquid nitrogen, in which a lesion is exposed to -321-degree temperatures, is also well-suited for removing smaller lesions. The exposed tissue will quickly form a blister that crusts over and falls off after several days.
• Shave excision is a reasonable option for small- to medium-size barnacles. Using a razor and a local anesthetic, the growth is shaved off and the wound is covered with an aluminum chloride or silver nitrate compound to stop the bleeding. Electrocautery may be used to feather the edges and reduce the appearance of the scar.
• Electrodissection and curettage (ED&C) is a procedure commonly used to treat BCC and SCC. It involves the scraping of the cancerous tissue with a device known as a curette, followed by the electrocautery to destroy the underlying cells. It is performed under local anesthesia and typically repeated three times to ensure all cancer cells are removed.

If a procedure is performed for cosmetic purposes, extra care needs to be taken for people with darker skin, as the removal of a lesion may leave a visibly lighter scar.

Seborrheic keratosis can sometimes be difficult to distinguish from melanoma, especially when a lesion first appears. As such, you should never make assumptions about any spots, patches, or lesions that develop on your body. See a dermatologist, or, if you have widespread keratosis schedule an annual exam to check parts of the body you cannot see yourself.