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Porokeratosis
  • Porokeratosis is a rare skin disorder characterized by skin lesions with a thin center surrounded by a distinctive ridge-like border.
  • Risk factors include genetic inheritance, exposure to ultraviolet light, and immunosuppression.
  • Five main types differ in appearance, location, and age of onset.
  • Single or combination topical, oral, or surgical therapies are beneficial but not curative.

The name porokeratosis, meaning scaly pore, was originally given to areas of abnormal skin tissue, or lesions, thought to develop from the pores of sweat glands.

We know now that porokeratosis was misnamed—it has no relation to pores. It’s a rare skin disorder that affects the maturation of skin cells, producing lesions with distinctive raised borders.

Here we will describe the different types of porokeratosis, as well as their treatment, complications, and prevention. But let’s begin by explaining how this condition really develops and the factors that contribute to it.

What is Porokeratosis?

As skin cells mature, they harden by accumulating a protein called keratin, a process called keratinization. Porokeratosis is a disorder of this process, resulting in the development of anywhere from a few to numerous skin lesions. They can be identified by their thin center surrounded by a distinctive ridge-like border made of protein-keratin, called the cornoid lamella.

Porokeratosis is classified as a rare disease, according to the Genetic and Rare Diseases Information Center of the National Institutes of Health. This means that each type affects fewer than 200,000 people in the United States.

What Causes Porokeratosis?

Although researchers still don’t know its underlying cause, they’ve identified the main risk factors contributing to its development:

Genetic Inheritance

All types can occur in family members, but sporadic genetic defects also occur (no family history).

Exposure to Ultraviolet (UV) Light

Porokeratosis is associated with a history of intense or long-term exposure to UV light.

Weakened Immune System

New or worsening lesions can develop with immunosuppression caused by therapy (e.g., chemotherapy, radiation therapy, organ transplant medications) or disease (e.g., AIDS, cancer, chronic renal failure, Crohn’s, diabetes, liver disease).

Sometimes people develop porokeratosis after skin trauma (e.g., burn wounds) or infections.

You’re more vulnerable to developing it if you have fair skin.

Keratosis Pilaris

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How Is Porokeratosis Diagnosed?

Porokeratosis is usually diagnosed by its appearance. According to East Greenwich, RI, dermatologist Caroline Chang, the characteristic rims surrounding the lesions are “well visualized with the assistance of a dermatoscope (polarized skin magnifier).”

Your doctor may also take a sample of the affected area to do a skin biopsy if necessary.

Types of Porokeratosis

There are five main types of porokeratosis. All types are rare, although the first two occur more frequently. You can develop more than one at once, or a second type after the first.

1) Disseminated Superficial Actinic Porokeratosis (DSAP)

  • Appearance: A few to numerous individual lesions or patches; skin-colored, brownish red, or brown; up to half an inch in diameter with a center surrounded by a raised brown ring.
  • Location/pattern: Commonly on sun-exposed areas, especially arms or legs, but forehead and cheeks in a small percentage of people. For those with a rare non-actinic variant, lesions can develop anywhere but spare the palms and soles.
  • Symptoms: Usually no symptoms, but may itch or sting.
  • Age when emerges: Usually adults in 30s or 40s; rarely affects children.
  • Frequency by sex: Affects women twice as often as men.
  • Contributing factors/associations: Genetic inheritance, especially if it occurs in female relatives, but can be sporadic; induced or worsened by immune suppression or extensive exposure to UV light; lesions often appear in summer and improve/disappear in winter; non-actinic form less likely to worsen with sun exposure.
  • Risk of cancer: Usually benign; squamous cell carcinoma occasionally develops but is uncommon (less than 10% of people with DSAP).

2) Classic Porokeratosis of Mibelli (PM)

  • Appearance: Initially small brownish lesions; remain unchanged or slowly grow over the years into larger plaques with a hairless center surrounded by a rim; less commonly, adult-onset lesions grow rapidly: “giant porokeratosis” lesions can grow to 8 inches.
  • Location/pattern: Typically on limbs, but can be anywhere, including hands, feet, neck, shoulders, face, genitals, and mucous membranes.
  • Symptoms: Usually no symptoms, but may itch.
  • Age when emerges: Usually childhood or young adulthood; lesions can be present at birth.
  • Frequency by sex: Affects men twice as often as women.
  • Contributing factors/associations: In adults, usually following immune suppression; can be triggered by UV exposure; occasionally associated with trauma (e.g., burn wound).
  • Risk of cancer: Squamous or basal cell carcinomas can develop, but more likely in older adults.

3) Linear Porokeratosis (LP)

  • Appearance: Papules and plaques bordered by a ring, with streaks of reddish-brown patches.
  • Location/pattern: Usually numerous grouped patches in lines along arms or legs, or on one side of trunk, head, or neck; patches can occur in one area (localized) or multiple areas (generalized).
  • Symptoms: Can itch or cause pain.
  • Age when emerges: Most often in infancy or early childhood, but sometimes in adulthood.
  • Frequency by sex: Equally frequent in males and females.
  • Contributing factors/associations: Considered a variant of DSAP; occasionally family history of LP or DSAP.
  • Risk of cancer: Higher risk of developing basal or squamous cell skin cancer than in all other types; more likely in older adults.

4) Porokeratosis Palmaris Et Plantaris Disseminata (PPPD)

  • Appearance: Numerous small, relatively uniform lesions.
  • Location/pattern: Palms and soles, but may spread anywhere, including mucous membranes.
  • Symptoms: Usually no symptoms, but sometimes itching, tenderness, or discomfort on soles.
  • Age when emerges: Any age from birth to adulthood.
  • Frequency by sex: Affects males twice as often as females.

5) Punctate Porokeratosis

  • Appearance: Numerous tiny bumps with thin raised margins.
  • Location/pattern: Palms and soles, but may slowly spread to other areas.
  • Symptoms: Usually no symptoms, but sometimes itching or discomfort on soles.
  • Age when emerges: Late childhood or early adulthood.
  • Frequency by sex: Unknown.
  • Contributing factors/associations: Other types of porokeratosis often develop.

Psoriasis

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What Are the Complications of Porokeratosis?

Most lesions are benign. On rare occasions (about 7.5% of patients), basal or squamous cell carcinoma — types of skin cancer — may develop. The greatest risk of developing a malignancy occurs in lesions that are large, have existed for a long time, or are linear.

But, as Dr. Rhonda Klein of the Connecticut Dermatology Group emphasizes, with DSAP, the “risk of progression to malignancy with porokeratosis is incredibly small.”

How Is Porokeratosis Treated?

For many people, all that is required is sun protection, moisturizers, and observation for malignancy.

But if you’re concerned about the appearance of your lesions, or if you experience dryness, itching, or pain, you may wish to explore treatment options with your dermatologist.

Various therapies can be helpful, especially for individual small lesions. Unfortunately, as Dr. Chang notes, “they usually recur after treatment is completed.”

Although there is no permanent cure, according to Dr. Klein, “a combination of oral treatments (imiquimod, fluorouracil, retinoids, etc.), excision and cryotherapy, fractional laser resurfacing, etc.” can be beneficial.

Topical Therapy

  • 5-Fluorouracil: May be effective for all types, but lesions may recur.
  • Vitamin D3 analog (e.g., calcipotriene, tacalcitol): May be effective for DSAP.
  • Retinoids (tretinoin, tazarotene): May reduce appearance of rims; may improve absorption of other topical therapies.
  • Diclofenac gel: May be effective for DSAP.
  • Imiquimod: May be effective for PM.
  • Calcineurin inhibitors (tacrolimus): May be effective for LP.

Oral Therapy

  • Retinoids (isotretinoin, acitretin): Isotretinoin may be effective for DSAP and PPPD when combined with topical 5-fluorouracil; acitretin may be effective for LP.

Surgical and Other Therapies

  • Excision: Essential with suspicion of malignancy; not useful for multiple lesions.
  • Cryotherapy (cold therapy): Has been effective for DSAP and PPPD; possibly used for small superficial basal and squamous cells.
  • Electrodessication and curettage (scrape and burn): Can be used to treat small lesions or if cryosurgery ineffective.
  • Laser therapy: Various types have been effective for DSAP, PM, and LP.
  • Photodynamic therapy: Has been effective for DSAP and LP; can be used for multiple lesions on a larger surface area; possibly used for small superficial basal and squamous cells.

What Can I Do to Prevent Porokeratosis?

Dr. Chang encourages sun avoidance for all skin disorders, but notes in particular that “those with DSAP should practice sun avoidance/protection to prevent progression of the disease.”

You cannot change your genetic inheritance, but you can take steps to prevent the development or recurrence of porokeratosis and reduce your risk of skin cancer. The American Academy of Dermatology offers these tips to protect your skin from UV light:

  • Seek shade, especially between 10 am and 2 pm.
  • Wear protective clothing and a wide-brimmed hat and sunglasses.
  • Generously apply a broad-spectrum, water-resistant sunscreen with a sun protection factor (SPF) of 30 or higher on all exposed skin, even on cloudy days. Reapply every 2 hours, or after swimming or sweating.
  • Avoid artificial tanning beds.
  • Perform regular skin self-exams.

If you notice a change in a porokeratosis lesion, ask your doctor for a prompt evaluation.

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