What Causes Porokeratosis and How Is It Treated?

Medically reviewed by Cynthia Cobb, DNP, APRN on September 12, 2017Written by Marjorie Hecht on September 12, 2017

What is porokeratosis?

Porokeratosis is a rare skin disorder affecting fewer than 200,000 Americans. It typically presents as small, round patches on your skin that have a thin, raised border.

Although the condition is usually benign, a small number of people may develop skin cancer within a lesion.

The disease was first identified in 1893 by Italian doctors Respighi and Mibelli. Since then, several variations have been identified. The six main subtypes are:

  • classic Mibelli porokeratosis (PM)
  • disseminated superficial porokeratosis (DSP)
  • disseminated superficial actinic porokeratosis (DSAP)
  • porokeratosis palmaris et plantaris disseminata (PPPD), also known as porokeratosis of Mantoux
  • linear porokeratosis (LP)
  • punctate porokeratosis (PP)

Keep reading to learn more about the different subtypes, including who’s at risk, what treatment options are available, and more.

What are the different subtypes?

Classic Mibelli porokeratosis (PM)

  • Appearance: These small brownish bump(s) may increase in size over time. The bumps have a prominent border with a thin ridge, which means the edges are easily identified and the bumps are slightly raised.
  • Location: Although it usually appears on a limb, it can develop anywhere.
  • Commonality: This is the second most common subtype.
  • Age of onset: It usually develops in children and young adults.
  • Risk by gender: Men are twice as likely to develop this type.
  • Triggers: These bumps may appear after light therapy, such as electron beam therapy and radiation therapy, and as a side effect of long-term topical steroid use.
  • Skin cancer: There’s a small chance that these lesions may develop into skin cancer, particularly if they cover a large area of skin.

Disseminated superficial porokeratosis (DSP)

  • Appearance: These round brownish lesions develop over a wide area of skin.
  • Location: It can develop anywhere on the body.
  • Commonality: This subtype is very rare.
  • Age of onset: It primarily affects children ages 5 to 10.
  • Risk by gender: There isn’t a clear indicator that men or women are more at risk.
  • Triggers: This subtype doesn’t have any clear triggers.
  • Skin cancer: There isn’t any information available to suggest that this type may become cancerous.

Disseminated superficial actinic porokeratosis (DSAP)

  • Appearance: This type presents as flesh-colored or reddish-brown round, scaly rings. These rings may be up to half an inch in diameter. They may itch or sting.
  • Location: It usually appears on the arms, legs, shoulders, or back.
  • Commonality: This is the most common subtype.
  • Age of onset: It typically affects adults in their 30s and 40s.
  • Risk by gender: Women are twice as likely to be affected by this subtype.
  • Triggers: This subtype has a genetic component. It may also result from extensive sun exposure, electron beam therapy and radiation therapy.
  • Skin cancer: This subtype is usually benign. Fewer than 10 percent of people with DSAP develop skin cancer within a lesion.

Porokeratosis palmaris et plantaris disseminata (PPPD)

  • Appearance: If features many small, uniform lesions that are typically the color of your skin. Some may have yellowish pits in the center. The lesions usually have little to no border.
  • Location: It primarily affects the palms and soles.
  • Commonality: This subtype is rare.
  • Age of onset: Although it usually affects people in their late teens and early 20s, it can also develop later in life.
  • Risk by gender: Men are twice as likely to be affected by this subtype.
  • Triggers: This subtype doesn’t have any clear triggers.
  • Skin cancer: There isn’t any information available to suggest that this type may become cancerous.

Linear porokeratosis (LP)

  • Appearance: It features many small and uniform reddish-brown lesions that arrange in lines along a limb or one side of the trunk.
  • Location: It primarily affects the palms and soles.
  • Commonality: This subtype is rare.
  • Age of onset: This form typically begins in infancy or early childhood.
  • Risk by gender: Women are at a slightly higher risk for this subtype.
  • Triggers: This subtype doesn’t have any clear triggers.
  • Reaction to sun: There isn’t any information available to suggest that this type may become cancerous.

Punctate porokeratosis (PP)

  • Appearance: These small lesions look like seeds. They typically have a thin outer edge.
  • Location: It primarily affects the palms and soles.
  • Commonality: This subtype is rare.
  • Age of onset: It typically develops during adulthood.
  • Risk by gender: There isn’t a clear indicator that men or women are more at risk.
  • Triggers: You may develop this subtype if you’re already affected by another form of porokeratosis.
  • Reaction to sun: There isn’t any information available to suggest that this type may become cancerous.

What porokeratosis looks like

Tips for identification

If you have a small, scaly patch of skin with a ridge-like border, it may be a form of porokeratosis. Your doctor or dermatologist can help with identification.

Here are some of the key characteristics:

  • The lesions can appear anywhere on your skin, including in your mouth or on your genitals.
  • Some types cover large areas of skin (DSP, DSAP, and PPPD) and others are more localized (PM, LP, and PP).
  • Some lesions can be itchy.
  • The two most common types, PM and DSAP, tend to be on your arms and legs.
  • The most common subtype, DSAP, may get worse in the summer and subside in the winter.
  • LP and PPPD begin on palms and soles but can spread elsewhere.
  • People with PP often develop another type.

What causes porokeratosis and who’s at risk?

The exact cause of porokeratosis isn’t known, and some study results have been contradictory.

Contributing factors may include:

Although the exact cause isn’t clear, researchers have identified a set of risk factors for this condition.

Your individual risk is determined by your:

  • Genes. If you have a parent with porokeratosis, you may inherit the damaged gene linked to the disease and develop the same type of porokeratosis.
  • Skin color. Fair-skinned people are more likely to develop porokeratosis.
  • Gender. Men are twice as likely to develop PM as women are. Women are more likely to have DSAP.
  • Age. Certain types develop in children (PM, DSP, and LP), young adults (PPPD), or adults (DSAP).

You may also be more at risk if you’re regularly exposed to direct sunlight. DSAP, the most common type, affects areas of the body exposed to sunlight. In studies, researchers have found that artificial sunlight has produced DSAP lesions.

How is it diagnosed?

Porokeratosis is usually diagnosed by its appearance. The thin raised edge around the lesion is present in all types, and is a major clue. But there are rare occurrences of a similar ridge appearing alongside other kinds of skin lesions, so your doctor may perform a biopsy to rule out other diagnoses.

Your doctor may also do a biopsy if it looks like a lesion may have a cancerous growth.

What treatment options are available?

Porokeratosis typically doesn’t require treatment. In benign cases, your doctor will monitor the lesions and watch for signs of malignancy.

In some cases, your doctor may prescribe topical or systemic drugs to help reduce your symptoms. There’s also evidence that laser treatments have improved the appearance of porokeratosis.

If you wish to have the lesions removed, your doctor may recommend:

What’s the outlook?

There’s no magic bullet for improving porokeratosis lesions in the short term. Talk with your doctor about what treatment options are available and how they may fit into your lifestyle.

Over the years, your porokeratosis may expand to cover more of your skin. Some types of porokeratosis, such as PM, LP, and PPPD, start out small and grow in time over larger areas.

All types of porokeratosis except PP come with a risk of developing a cancerous growth in a lesion, usually a squamous cell carcinoma. An estimated 7.5 to 11 percent of people with porokeratosis go on to develop a cancerous growth.

How to protect your skin

Although porokeratosis is generally benign, you should keep a close eye on your lesions. If you notice any change in color or size, see your doctor.

The most important way to prevent porokeratosis from worsening or becoming malignant is to protect yourself from UV rays.

In addition to limiting direct sun exposure, you should always wear sunscreen with an SPF of 30. You should also wear UV-protectant clothing, a wide-brimmed hat, and sunglasses for added protection.

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