Disseminated Superficial Actinic Porokeratosis
Porokeratosis, which was first described by Mibelli and Respighi in 1893, is a genetic dermatologic condition that has at least 4 recognized variants: porokeratosis palmaris et plantaris disseminate, linear porokeratosis, porokeratosis of Mibelli, and disseminated superficial actinic porokeratosis (DSAP).1 DSAP is the most common form of porokeratosis and was differentiated as a separate variant by Chernosky in 1966.2 It is a disorder of keratinization that is characterized by multiple keratotic papules that appear in sun-exposed areas of the skin.3
DSAP is inherited in an autosomal-dominant fashion and is incompletely penetrant; development of symptoms may depend on other environmental factors. Mutations in genes related to keratinocyte differentiation and proliferation have been identified as causes for the disease.4 Histologically, porokeratosis shows cornoid lamella (characteristic columns of parakeratotic cells), dyskeratotic cells, the absence of a granular cell layer, and an irregularly thin epithelium in the affected area.3 The cornoid lamella of DSAP lacks the central groove and is smaller than the cornoid lamella observed in classic porokeratosis.2 Other histologic findings include perivascular mononuclear lymphocytic infiltrate in the dermal layer. Because histology is similar among all types of porokeratosis, DSAP can also be differentiated based on other clinical factors, such as the location and appearance of lesions and age at onset. DSAP is slightly more common in women than in men (1.76:1). It is predominantly observed in lighter skin pigmentation and is most common in whites, particularly those of Italian heritage.3
Clinically, DSAP first presents as scattered cone-shaped plaques measuring 1 to 3 mm in diameter in follicular locations.2 As these lesions grow, they develop atrophic, erythematous, or keratotic centers and well-defined, raised, hyperkeratotic rims that may be round or irregular. Over time, they can grow to >3 cm in diameter.4 They usually appear on areas of the body that are exposed to sunlight, including the limbs, shoulders, and back. The face is affected in only 15% of patients, despite its exposure to the sun.3 Because ultraviolet (UV) sunlight is an exacerbating factor, patients often experience worsening of symptoms during the summer months.1
Although DSAP can develop during adolescence, it usually appears during the third or fourth decades of life and progresses slowly afterward. The phenotype of the disease is variable; some patients with DSAP are asymptomatic with lesions that are mistaken for other forms of sun damage,2 while approximately one-third of patients experience pruritus or pain with their lesions.3 In addition to UV exposure and genetic predisposition, risk factors for DSAP include immunosuppression, with new cases arising in patients following organ transplant and those with AIDS.1,3 DSAP is usually benign but has been associated with the development of cutaneous malignancies in 3.4% of patients; the most common malignant lesions originating from porokeratosis are epidermoid carcinoma, carcinoma in situ, and basal cell carcinoma.5
The differential diagnosis of DSAP includes actinic keratosis, Darier disease, psoriasis, hereditary punctate keratoderma, porokeratotic eccrine ostial and dermal duct nevus, and lichen nitidus. Certain clinical factors such as the location of the plaques, age at onset, exacerbating factors, and appearance of the rash are important for the differentiation of DSAP from these other conditions. For example, porokeratotic eccrine ostial and dermal duct nevus is characterized by keratotic plaques on the extremities but is present at birth or within the first few years of life.6 In addition, the characteristic cornoid lamella on histology differentiates porokeratosis from other skin disorders. Imaging techniques such as optical coherence tomography and fluorescence confocal microscopy are also used to diagnose DSAP and differentiate it from actinic keratosis.3
A variety of methods have been used to treat DSAP, although controlled trials are lacking and data are mostly limited to case reports. The size, location, and malignancy of the lesions dictate the treatment approach. For many patients, use of moisturizers, avoidance of sunlight, and regular skin checks are sufficient methods for disease control. However, treatment modalities for more complicated cases include topical treatments, systemic treatments, laser therapy, and surgical approaches.3
Topical treatments such as 5-fluorouracil, retinoids, glucocorticoids, and salicylic acid have been used with varying degrees of success. For example, 5-fluorouracil is not always an appropriate method of treatment for DSAP because it results in an inflammatory reaction. Systemic treatments such as oral retinoids have been used successfully for DSAP, but relapse may occur and prolonged use is associated with adverse effects. The use of CO2 laser therapy or ruby laser therapy can improve the appearance of DSAP-associated lesions, but recurrence is common.7 In patients with only a few large plaques or malignant lesions, surgical removal may be the treatment method of choice, although this results in scarring.3
After discussion of the various treatment options, the patient opted for short-term therapy with oral retinoids. At follow-up evaluation, his symptoms were noted to have improved.
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