February 2015 Dermatology Clinic
A woman, aged 52 years, presents with a rash on her legs, noting that round brown spots appeared on the front of her shins and multiplied over a course of a few months. The lesions are not painful but are itchy at times. The patient has a history of outdoor tanning on the weekends as a teenager and young adult.
Physical examination reveals light brown and orange macules, patches, and plaques, many of which had a raised keratotic peripheral border. Most of the rash was on her anterior shins, but some lesions were also on the posterior shins. Full skin examination showed multiple lentigines on the face, trunk, and extremities, and actinic keratoses on the face.
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Porokeratosis is a disorder of keratinization. The subtype, disseminated superficial actinic porokeratosis (DSAP), is an autosomal dominant inherited disorder expressed in the sun-exposed areas of fair skinned adults. It is considered a premalignant condition, because of its association with skin cancer and its immunohistochemical similarities to actinic keratosis and squamous cell carcinoma.
The typical appearance of DSAP is a symmetrical distribution of brown annular plaques with a thickened raised border and a lightly atrophic center. The lesions are most commonly distributed on the extensor surfaces of the legs (84%) and extensor surfaces of the arms (78%).1 The trunk and face are rarely affected. The lesions are usually asymptomatic, although some patients complain of intermittent associated pruritus.
Although DSAP has classically been shown to be expressed after outdoor sun exposure, the condition can also be induced by the use of indoor tanning beds. In addition, 1 case study reports induction of DSAP following ultraviolet (UV) B phototherapy for the treatment of psoriasis2 and another report describes the appearance of DSAP after treatment with a combination of psoralen and UVA (PUVA).3 In the rare cases in which DSAP appears in areas not exposed to UV radiation, it is usually associated with immunosuppression and malignancy.4
DSAP typically appears between the third and fourth decade of life. Both sexes are affected, but women typically have more lesions on the legs, and men have more lesions on the arms.
The malignant potential of DSAP has been documented, but the exact risk is unknown. One study showed a 7.5% rate of malignancy5 developing within a preexisting porokeratosis. The risk for developing malignancy appears to be higher in larger and longstanding lesions.
Histologic examination of a skin biopsy specimen reveals a cornoid lamella, which consists of a vertical column of tightly packed parakeratotic cells. This corresponds to the clinical peripheral raised keratotic edge. In addition, epidermal atrophy, solar elastosis, and an inflammatory dermal infiltrate are also often noted.
The clinical differential diagnosis for DSAP include other annular rashes, such as tinea corporis, tinea versicolor, nummular eczema, and psoriasis. Other hyperpigmented lesions and rashes on the legs that are often confused with DSAP include lentigines, macular seborrheic keratosis, and Schamberg disease.
Treatment of DSAP is often challenging and frustrating to both patient and clinician. Protection from the sun and close observation for malignant transformation with annual skin exams is often sufficient for those that do not seek improvement of the rash. However, many patients request treatment due to associated pain or pruritus or for cosmetic benefit. Suggested topical treatments include vitamin D analogues such as calcipotriol and tacalcitol, retinoids, immunomodulators, and 5-fluorouracil; these often require weeks of treatment. Muellenhoff and Tran suggested treatment with a topical gel of 3% diclofenac sodium.6
Surgical care may involve cryotherapy, laser, electrodessication and curettage, or dermabrasion, but these procedures may result in unacceptable scarring. In a small study, Schmook et al. compared the effectiveness of imiquimod, photodynamic therapy, and cryotherapy. They found cryosurgery with 1 freeze-thaw cycle to be the most effective technique for DSAP.7 Lebwohl et al. recommended cryotherapy as a first-line treatment.8
With any treatment choice, patients should be educated regarding the need for strict sun and UV protection to avoid new lesions. They should also be instructed to observe the existing lesions for any changes, which may indicate malignant transformation. In addition to monitoring their skin for new or changing lesions, patients should undergo an annual full-skin examination by a dermatology provider.
The patient above was educated regarding the diagnosis and its clinical implications. We discussed the need for strict sun protection and regular skin examinations. Although the lesions were intermittently itchy, the patient elected not to treat the condition, but rather to closely observe for signs of malignant transformation.
Esther Stern, NP-C, is a family nurse practitioner at Advanced Dermatology & Skin Surgery, P.C., in Lakewood, N.J.
- Schwarz T, Seiser A, Gschnait F. Disseminated superficial “actinic” porokeratosis. J Am Acad Dermatol. 1984;11(4 Pt 2):724-730.
- Cockerell CJ. Induction of disseminated superficial actinic porokeratosis by phototherapy for psoriasis. J Am Acad Dermatol. 1991;24(2 Pt 1):301-302.
- Allen AL, Glaser DA. Disseminated superficial actinic porokeratosis associated with topical PUVA. J Am Acad Dermatol. 2000;43(4):720-722.
- Crittenden S, Burch A. Disseminated superficial porokeratosis in an immunocompetent patient. J Am Acad Dermatol. 2013;68(4 Suppl 1):AB197.
- Sasson M, Krain AD. Porokeratosis and cutaneous malignancy. A review. Dermatol Surg. 1996;22(4):339-342.
- Muellenhoff MW, Tran T. Topical 3% diclofenac sodium gel, a novel treatment of disseminated superficial actinic porokeratosis. J Am Acad Dermatol. 2004;50(3):P40. Available at eblue.org/article/S0190-9622(03)03496-0/fulltext
- Schmook T, Kraft J, Ulrich C, Stockfleth E. Disseminated superficial actinic porokeratosis: Report of 7 patients successfully treated with cryotherapy. J Am Acad Dermatol. 2005;52(3):P159. Available at eblue.org/article/S0190-9622(04)03417-6/fulltext
- Martin-Clavijo A, Kanelleas A, Vlachou C, Berth-Jones J. Porokeratoses. In Lebwohl MG, Heymann WR, Berth-Jones J, Coulson I, eds. Treatment of Skin Disease. 3rd ed. St. Louis, Mo.: Saunders Elsevier; 2010:584-587.
All electronic documents accessed on January 29, 2015.