Derm Dx: Small annular plaques on the legs - Clinical Advisor

Derm Dx: Small annular plaques on the legs

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A woman in her sixties presents complaining of a progressive rash on her legs. The rash consists of multiple small annular plaques. The patient does not complain of any pruritus or pain. She states that her mother had the same condition.

Porokeratosis of Mibelli was first described in 1893. The classic lesion is a hyperkeratotic annular papule or plaque with a raised thread-like border. At least several different types of porokeratosis have been described including, disseminated superficial actinic porokeratosis (DSAP), linear...

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Porokeratosis of Mibelli was first described in 1893. The classic lesion is a hyperkeratotic annular papule or plaque with a raised thread-like border. At least several different types of porokeratosis have been described including, disseminated superficial actinic porokeratosis (DSAP), linear porokeratosis, punctate porokeratosis and porokeratosis palmaris et plantaris disseminata.

This patient was diagnosed with DSAP, the most common form of porokeratosis, which consists of small annular papules with the thread-like raised border located on sun-exposed areas of the extremities. The lesions vary in appearance from skin-colored to red keratotic papules and may be asymptomatic or mildly pruritic.

Frequently, the border of these lesions spread, becoming elevated and thread-like as the center atrophies. This condition is most commonly seen on the lower extremities of adult women.

DSAP has also been reported to worsen during months of more concentrated sun exposure. It may be mistaken as multiple actinic keratoses, but examining the location of involvement can differentiate the lesions. Contrary to the typical facial location of actinic keratosis, DSAP almost never involves the face. Additionally, actinic keratoses lack the characteristic thread-like border. 

Risk factors for developing DSAP condition include exposure to UV light, family history and immunosuppression.  If inherited, porokeratosis is an autosomal dominant condition. The genetic alteration in DSAP has been linked to multiple loci on chromosomes 1, 12, 15 and 18. 

Porokeratosis of Mibelli, the classic form of the disorder, typically presents prior to adolescence. The lesions are skin-colored to brown keratotic papules with a raised keratotic border and can be localized to any part of the body, especially the extremities. 

Linear porokeratosis erupts in a Blaschkoid distribution involving the extremities. Porokeratosis palmaris et plantaris disseminata is a more rare form of porokeratosis. The lesions are more inconspicuous compared to the classic form, affecting the palms and soles with possible mucous membrane involvement. 

Punctate porokeratosis may present as small, discrete keratotic papules involving the palms and soles of children and often must be differentiated from Darier disease, punctate keratoderma, arsenical keratosis and Cowden disease. The risk of developing a squamous cell carcinoma within the lesion is greatest for linear porokeratosis.

The characteristic histologic feature of all forms of porokeratosis is the cornoid lamella, which is a column of parakeratosis with an absent underlying granular layer. 

Treatment for all forms of porokeratosis is difficult. Many modalities of treatment have been utilized for porokeratosis including topical retinoids, imiquimod, excision, cryotherapy, CO2 laser, curettage and dermabrasion with variable results.

These lesions have a high tendency to recur. In the case of DSAP, treatment options may also include systemic agents such as oral acitretin. In order to reduce the recurrence and progression rate, it is recommended to educate patients afflicted with this condition on the importance of adequate sun protection. 

Reid Green, BS, is a senior medical student at the University of Central Florida College of Medicine.

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.

References

  1. Bolognia J, Jorizzo JL, Rapini RP. “Chapter 52: Dermatologic Manifestations in Patients with Systemic Disease.” Dermatology. St. Louis: Mosby/Elsevier, 2008.
  2. James WD, Berger TD, Elston DM et al. ” Chapter 24: Endocrine Diseases.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunders Elsevier, 2006.
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