AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

Section 2 of 11  

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Background

Porokeratosis is a clonal disorder of keratinization characterized by 1 or more atrophic patches surrounded by a clinically and histologically distinctive ridgelike border called the cornoid lamella. Five clinical variants of porokeratosis are recognized: classic porokeratosis of Mibelli (PM), disseminated superficial actinic porokeratosis (DSAP), porokeratosis palmaris et plantaris disseminata (PPPD), linear porokeratosis, and punctate porokeratosis. Several other variants have been described, including hyperkeratosis types, a pruritic papular variant, and an unusual verrucous variant that is localized to the buttocks and mimics psoriasis. Occasionally, a patient may develop more than one type of porokeratosis.

Pathophysiology

Clonal hyperproliferation of atypical keratinocytes leads to the formation of the cornoid lamella, which expands peripherally and forms the raised boundary between abnormal and normal keratinocytes. Local or systemic changes in immune function may allow the development of atypical clones of keratinocytes. Loss of heterozygosity has been proposed as a mechanism for linear porokeratosis associated with a personal or family history of DSAP.

Several risk factors for the development of porokeratosis have been identified; these factors include genetic inheritance, ultraviolet radiation, and immunosuppression. Immunosuppression associated with porokeratosis may be secondary to a disease process such as HIV infection or lymphoma or an iatrogenic suppression such as with immune-modulating drugs used to prevent organ transplant rejection or to treat autoimmune diseases. An autosomal dominant mode of inheritance has been established for familial cases of all forms of porokeratosis. Sun exposure is thought to cause DSAP, although the typical sparing of facial skin is unexplained. Excessive natural or artificial ultraviolet radiation, electron beam therapy, and extensive radiation therapy are well-established trigger factors. Immunosuppression may induce new lesions or cause preexisting lesions to flare.

The formation of squamous or basal cell carcinomas has been reported in all forms of porokeratosis. Chromosomal instability and reduced immune surveillance with overexpression of p53 are hypothesized to play a role in the development of cutaneous malignancies within porokeratosis.

Frequency

United States

DSAP is relatively common. The other forms of porokeratosis are rare.

Mortality/Morbidity

• Most lesions are asymptomatic. Ulcerative lesions have been described. Giant PM in a facial or acral location may cause destruction of underlying soft tissue or pseudoainhum with amputation.
• Malignant degeneration has been reported in all forms of porokeratosis, with risks of 7.5% and 11% determined from two published review of the literature. Large lesions, lesions of long-standing duration, and the linear type of porokeratosis were found to be at greatest risk. A squamous cell carcinoma developing within a large PM lesion, associated with extensive metastases and hypercalcemia, has been reported.

Race

• Porokeratosis most commonly occurs in fair-skinned individuals. It is rare in darker-skinned populations.

Sex

• PM and PPPD affect men twice as often as women.
• DSAP is 3 times as likely to develop in women compared with men.
• Linear porokeratosis is seen with equal incidence in men and women.

Age

• PPPD and linear porokeratosis may be seen at any age, from birth to adulthood.
• PM usually develops in childhood (see Media File 1).
• Disseminated superficial porokeratosis (DSP) generally develops in the third or fourth decade of life.

CLINICAL

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History

• Classic porokeratosis (Mibelli)
• • During childhood, a small, asymptomatic or slightly pruritic lesion develops, expanding over a period of years.
  • Less commonly, lesions may develop during adulthood and enlarge rapidly, usually in the clinical setting of immunosuppression.
  • Occasionally, patients have a history of an antecedent trauma, such as a burn wound.
• Disseminated superficial (actinic) porokeratosis
• • Multiple, brown, annular, keratotic lesions that develop predominantly on the extensor surfaces of the legs and the arms characterize DSAP. They are usually asymptomatic, but they may itch slightly (see Media File 2). Sunless tanning lotions containing dihydroxyacetone cause the cornoid lamellae to darken and become more clinically prominent. Dermoscopy reveals a "white track" structure with brown pigmentation on the inside of the track that can be seen at the edge of an individual lesion, corresponding to the cornoid lamella. Centrally, a white area with red dots, globules, and lines is present that corresponds to capillary vessels; it is more easily observed through the atrophic epithelium.
  • Facial lesions are seen in approximately 15% of patients, but the face may be the only area of involvement.
  • Patients are typically women in their third or fourth decade of life, with a history of excessive ultraviolet exposure.
  • Patients may have a history of phototherapy for psoriasis.
  • Nonactinic forms may be seen following electron beam total skin irradiation, organ transplantation, hepatitis C virus–related hepatocellular carcinoma, HIV infection, renal failure, or in association with other causes of immunosuppression.
• Linear porokeratosis: During infancy or early childhood, a unilateral, linear array of papules develops. The patient may notice changes consistent with malignant degeneration later in life.
• Porokeratosis palmaris et plantaris disseminata
• • Small, relatively uniform lesions are first seen on the palms and the soles, and, then, they develop in a generalized distribution, including the mucosal membranes.
  • The lesions may itch or sting, but they are usually asymptomatic.
  • The onset is typically during adolescence or early adulthood, and males are affected twice as often as females.
• Punctate porokeratosis: Multiple, asymptomatic, tiny, hyperkeratotic papules with thin, raised margins develop on the palms and the soles during adulthood.

Physical

• Classic porokeratosis (Mibelli)
• • The lesion develops as a small, light brown, keratotic papule that slowly expands to form an irregularly shaped, annular plaque with a raised, ridgelike border. This border may be hypertrophic or verrucous and is usually greater than 1 mm in height. A thin furrow is typically seen in the center of the ridge, causing a Great Wall of China effect. The lesion is slightly hypopigmented or hyperpigmented, minimally scaly, slightly atrophic, hairless, and anhidrotic. The size may vary from a few millimeters to several centimeters.
  • Lesions may be found anywhere, including the mucous membranes, although they most commonly occur on the extremities. Generally few lesions are observed. A verrucous variant that is localized to the buttocks and resembles psoriasis has been reported in several patients.
• Disseminated superficial (actinic) porokeratosis
• • Dozens of small, indistinct, light brown patches with a threadlike border are seen on the extensor surfaces of the arms and the legs.
  • Dermoscopy shows a "white track" structure at the periphery of the lesion, with a brownish pigmentation on the inner side and with a double white track in some parts of the lesion. This corresponds to the cornoid lamella. The center may show a white homogeneous area, corresponding to acanthotic epithelium, or red dots, globules, and lines corresponding to enlarged capillary vessels that can be seen because the epithelium is atrophic.
  • Facial lesions are seen in approximately 15% of patients.
  • Nonactinic DSP may have a generalized distribution, sparing the palms and the soles.
  • Bullous and pruritic variants have been described.
• Linear porokeratosis
• • Grouped, linearly arranged, annular papules and plaques with the characteristic raised peripheral ridge are seen unilaterally on an extremity, the trunk, and/or the head and neck area. The lesion commonly follows a dermatomal distribution.
  • Multiple linear groups may be seen in one patient, typically on the same side. They may be seen in association with other forms of porokeratosis.
  • Individual lesions within the linear grouping have a well-developed border, often with a central furrow similar to that seen in classic PM.
  • Clinical changes consistent with the development of a basal or squamous cell carcinoma are more common in linear porokeratosis than in other forms of porokeratosis.
• Porokeratosis palmaris et plantaris disseminata
• • The lesions are small, superficial, relatively uniform, with a slightly hyperpigmented, atrophic center and a minimally raised peripheral ridge. Mucosal lesions are small, annular or serpiginous, and pale.
  • Squamous cell carcinoma has been reported to develop within lesions of PPPD.
• Punctate porokeratosis
• • Dozens of discrete or grouped seedlike hyperkeratotic lesions with characteristic thin, raised ridgelike margins develop on the palms and the soles. Patients usually have other forms of porokeratosis as well, most commonly the linear or Mibelli types.
  • Punctate porokeratosis may be clinically and histologically indistinguishable from punctate porokeratotic keratoderma, which is considered to be a cutaneous sign of an internal malignancy.

Causes

Risk factors for porokeratosis include genetic inheritance, ultraviolet light exposure, and immunosuppression. One study found that approximately 10% of patients who had undergone renal transplantation developed porokeratosis.

• Classic porokeratosis (Mibelli)
• • Autosomal dominant inheritance and immunosuppression are the usual causes.
  • PM has been seen following radiation therapy, at burn wounds, and at hemodialysis sites.
• Disseminated superficial (actinic) porokeratosis
• • Sun exposure and/or artificial ultraviolet radiation exposure in a patient who is genetically predisposed causes DSAP. Exacerbations have been reported following prolonged sun exposure, repeated tanning bed exposure, electron beam radiation therapy, and therapeutic phototherapy or photochemotherapy for psoriasis. Drug-induced photosensitivity may play a role. Protection from ultraviolet radiation may lead to spontaneous resolution.
  • Immunosuppression predisposes patients to both DSAP and nonactinic DSP. Because of this, a viral etiology has been hypothesized.
• Linear porokeratosis
• • No definite inheritance pattern has been established.
  • Loss of heterozygosity has been proposed as a genetic mechanism and may explain the higher risk of malignant degeneration seen in linear porokeratosis in comparison to other forms of porokeratosis.
• Porokeratosis palmaris et plantaris disseminata
• • Familial PPPD is transmitted in an autosomal dominant mode with variable penetrance.
  • Acquired PPPD may be caused by immunosuppression, or it may be a cutaneous marker of internal malignancy.
• Punctate porokeratosis: This condition has no unique inheritance pattern and is usually associated with other forms of porokeratosis.

DIFFERENTIALS

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Other Problems to be Considered

Linear verrucous epidermal nevus
Porokeratotic eccrine ostial and dermal duct nevus

WORKUP

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Lab Studies

• Generally, no laboratory studies are required.
• Screening for diseases causing immunosuppression (eg, HIV, hematologic malignancies) and/or renal failure is appropriate when new lesions of PM or DSP are seen or when sudden exacerbation of any form of porokeratosis develops.

Histologic Findings

The cornoid lamella is the histopathologic hallmark of all forms of porokeratosis. It is essential that the specimen be taken from the peripheral, raised, hyperkeratotic ridge to demonstrate this finding.

The cornoid lamella consists of a thin column of tightly packed parakeratotic cells within a keratin-filled epidermal invagination. The parakeratotic column extends at an angle away from the center of the lesion and develops from the interfollicular epidermis, but it may involve the ostia of hair follicles or sweat ducts. Within the parakeratotic column, the horny cells appear homogeneous and possess deeply basophilic pyknotic nuclei. In the epidermis beneath the parakeratotic column, the keratinocytes are irregularly arranged and have pyknotic nuclei with perinuclear edema. No granular layer is seen within the parakeratotic column, while the keratin-filled invagination of the epidermis has a well-developed granular layer. The papillary dermis beneath the cornoid lamella contains a moderately dense, lymphocytic infiltrate and dilated capillaries. Dermal amyloid deposits have been described in some cases of DSAP.

Specimens taken from the center of the lesion show atrophy, with areas of liquefaction degeneration in the basal layer, colloid-body formation and flattening of rete ridges. The dermis may be edematous or fibrotic with telangiectasia. Amyloid deposition may be seen in the papillary dermis, both centrally as well as beneath the cornoid lamellae. The cornoid lamella is prominent in PM but less distinct in DSAP, DSP, and PPPD. At the ultrastructural level, vacuolization of keratinocytes, clumping of keratin filaments, and a paucity of lamellar bodies are found. Intercellular lamellar sheets are incompletely formed and may be responsible for defective desquamation.

Immunohistochemical studies show that keratinocytes beneath the cornoid lamella stain in a pattern similar to that observed in squamous cell carcinomas. Keratinocytes central to the cornoid lamella stain in a pattern identical to that of premalignant lesions, such as actinic keratosis. Keratinocytes peripheral to the cornoid lamella stain normally.

TREATMENT

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Medical Care

The approach to treatment must be individualized, based on the size of the lesion and the anatomical location, the functional and aesthetic considerations, the risk of malignancy, and the patient's preference. Protection from the sun, use of emollients, and watchful observation for signs of malignant degeneration may be all that is needed for many patients. If lesions are widespread and medical treatment is desired, several medications have potential benefit.

• Topical 5-fluorouracil: Topical 5-fluorouracil can induce remission in all forms of porokeratosis. Treatment must be continued until a brisk inflammatory reaction is obtained. Enhancement of penetration, which heightens the response, may be achieved by occlusion or the addition of topical tretinoin. Concurrent use of topical steroids may ease discomfort without reducing long-term improvement. Recurrences may be seen.
• Topical vitamin D-3 analogues: Both calcipotriol and tacalcitol have been shown to be effective after 3-6 months of treatment of DSAP.
• Topical imiquimod 5% cream: This has been shown to be effective for treating PM.
• Oral retinoids (isotretinoin, etretinate, and acitretin): The use of oral retinoids in patients who are immunosuppressed, who are at higher risk for malignant degeneration, may reduce the risk of carcinoma in porokeratotic lesions.
• • Oral isotretinoin at 20 mg daily combined with topical 5-fluorouracil is reported to be effective for DSAP and PPPD, but it causes burning, itching, and painful erosions.
  • Reports of etretinate efficacy are conflicting. Etretinate at doses of 75 mg/d for 1 week followed by 50 mg/d has been shown to be helpful in linear porokeratosis and symptomatic PM. Higher doses of 1 mg/kg/d were reported to exacerbate lesions of DSAP after 4-6 weeks of treatment. Even when etretinate therapy is successful, relapses may occur. Digitate keratoses were reported to develop after the use of etretinate for DSAP.
  • Acitretin, a second-generation monoaromatic retinoid that is the active metabolite of etretinate, is likely to have results similar to those of etretinate. However, no studies have reported the effect of acitretin on porokeratosis.

Surgical Care

Surgical treatment is essential for porokeratosis lesions that have undergone malignant transformation. No studies showing the value of prophylactic nonexcisional surgical treatment in reducing the incidence of malignancy within porokeratosis have been reported. Surgical modalities other than excision may improve cosmesis and/or function but are frequently followed by relapses.

• Excision is most appropriate when malignant degeneration develops.
• Cryotherapy is helpful for porokeratosis lesions with minimally raised cornoid lamellae, such as DSAP and PPPD. It is a minimally invasive method of inducing resolution for large numbers of lesions.
• Electrodesiccation and curettage can be used to treat small lesions or when cryosurgery is ineffective.
• Diamond fraise dermabrasion has been used with conflicting reports of efficacy. It was effective in improving the appearance of linear porokeratosis in one patient, but a child with a large PM lesion had recurrence after treatment.
• Laser therapy
• • A rapid recurrence reportedly followed carbon dioxide laser ablation.
  • The 585 nm flashlamp-pumped pulsed dye laser was shown to help one patient with linear porokeratosis. Another patient with PM with an underlying hemangioma had good improvement of the hemangioma but no change in the porokeratosis after treatment.
  • The frequency-doubled Nd:YAG laser was shown to be helpful for one patient with DSP.
• Ultrasonic surgical aspiration was shown to be effective in the treatment of vulvar porokeratosis in one patient.
• Photodynamic therapy with methyl aminolevulinate was reported to be successful for treatment of DSAP.

MEDICATION

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The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Drug Category: Antimetabolites

These agents inhibit cell growth and proliferation.

Drug Category: Vitamin D analogues

These agents regulate calcium-induced keratinocyte differentiation. Tacalcitol has been used, but it is not available in the United States.

Drug Category: Retinoids

These agents decrease the cohesiveness of abnormal hyperproliferative keratinocytes and may reduce the potential for malignant degeneration. They modulate keratinocyte differentiation and have been shown to reduce the risk of skin cancer formation in patients who have undergone renal transplantation.

FOLLOW-UP

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Further Inpatient Care

• Inpatient care is rarely necessary.

Further Outpatient Care

• Regularly monitoring patients for the development of malignant transformation is essential, especially in the setting of immunosuppression. Squamous cell or basal cell carcinomas can be aggressive in patients who are immunosuppressed.

Complications

• The development of cutaneous malignancy is the most important complication to watch for.
• Functional impairment due to involvement of critical anatomical locations may develop. Prophylactic excision should be considered in appropriate situations.

Prognosis

• The prognosis is generally excellent. This is especially true for DSP. Clinical settings of concern include the following:
• • Patients who develop PM or linear porokeratosis because of immunosuppression are at higher risk for the development of a squamous or basal cell carcinoma within the lesion. These cutaneous malignancies often behave aggressively, with the potential for extensive local tissue destruction (basal cell carcinoma) and distant metastasis (squamous cell carcinoma).
  • Linear porokeratosis is associated with a higher risk of malignant degeneration.
  • PM circumferentially involving the digits may induce pseudoainhum.

Patient Education

• Patients must practice strict sun precautions. These measures include wearing protective clothing; applying sunblock; avoiding exposure to midday sunlight; and discontinuing exposure to artificial ultraviolet light, such as tanning beds and therapeutic phototherapy.
• Patients must periodically examine their skin for lesions suggestive of malignancy. A qualified physician should promptly evaluate any change in a porokeratosis lesion.
• Family members should be examined for porokeratosis if familial porokeratosis is suspected.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to screen for immunosuppression or renal failure in a patient who presents with sudden exacerbation of preexisting lesions or who develops PM, linear porokeratosis, PPPD, or nonactinic DSP is a pitfall.
• Failure to screen for an internal malignancy in adult patients who develop PPPD is a pitfall.
• Failure to monitor for malignant transformation in all patients with porokeratosis, especially in patients with linear porokeratosis and in patients who are immunosuppressed, is a pitfall. Early detection and margin-controlled excision is important because these malignancies may be aggressive.

MULTIMEDIA

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Media file 1:  Porokeratosis of Mibelli on the lower leg in a renal transplant recipient.
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Media type:  Photo

Media file 2:  Disseminated superficial actinic porokeratosis on the lower legs of a female patient.
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Media type:  Photo

Media file 3:  A 42-year-old woman with multiple lesions on the pretibial aspects of the legs.
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Media type:  Photo

REFERENCES

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Article Last Updated: Mar 9, 2007