Disseminated superficial actinic porokeratosis is the most common subtype of porokeratosis, a keratinization disorder. There are 6 subtypes of porokeratosis identified in the literature: DSAP, disseminated superficial porokeratosis, classic porokeratosis of Mibelli, porokeratosis plantaris palmaris et disseminata, linear porokeratosis, and punctate porokeratosis.6 Disseminated superficial actinic porokeratosis has a female predominance (1.8:1 ratio)7 and generally appears in the third or fourth decades of life. Clonal proliferations of atypical keratinocytes have been implicated in the etiology of DSAP; however, the exact pathogenesis is unclear. Risk factors for DSAP include genetic susceptibility (eg, autosomal-dominant inheritance pattern), exposure to UV radiation, and drug-related immunosuppression or immunodeficiency.7 Other proposed etiologic risk factors include trauma and infection.8 Clinical diagnosis of DSAP is confirmed by the histological presence of a cornoid lamella (a thin column ofparakeratotic cells), a thinning epidermis, an absent or thinned granular cell layer, and a prominent dermal lymphocytic infiltrate.9,10
Disseminated superficial actinic porokeratosis clinically presents as small atrophic scaly papules and/or patches with raised peripheral ridges symmetrically dispersed on sun-exposed areas of the arms, legs, back, and shoulders. Although these lesions are extensive, they typically spare the mucous membranes, palms, and soles11; only a small percentage of cases report facial lesions,12 which often are asymptomatic but cosmetically bothersome. Additionally, approximately half of patients report symptoms of pruritus and/or stinging,13 thus treatment of DSAP is mainly indicated for symptomatic relief and cosmetic purposes. Malignant degeneration14,15 occurs in approximately 7.5% to 11% of porokeratosis cases,10,16 warranting treatment for preventative measures.
Management of DSAP is dependent on the extent of the disease and the level of concern for malignant transformation. Localized disease can be treated with cryotherapy, CO2 laser, and/or ablative techniques (eg, excision, curettage, dermabrasion) with variable degrees of success but high risk for scarring.1 More extensive disease requires treatment with topical retinoids, topical 5-fluorouracil, imiquimod cream 5%, diclofenac gel 3%, topical vitamin D3 analogues, and photodynamic therapy.1 Several other therapies have been reported in the literature with partial and/or complete success, including systemic retinoids (eg, acitretin), Q-switched ruby laser, Nd:YAG laser, fractional photothermolysis, Grenz rays, pulsed dye laser, fractional photothermolysis, topical corticosteroids, and fluor-hydroxy pulse peel.6 Although there is an extensive array of therapies for DSAP, treatment results are variable with mostly limited success. Successful treatment of DSAP is difficult and often requires the use of multiple modalities.
Ingenol mebutate is the active compound found in the sap of Euphorbia peplus used for the topical treatment of various skin conditions, including AKs.17 Ingenol mebutate gel 0.05% once daily for 2 days has been approved by the US Food and Drug Administration for the topical treatment of AKs. The mechanism of action of ingenol mebutate in AK therapy is not yet fully understood. In vivo and in vitro models have demonstrated both an induction of local lesion cell death and promotion of lesion-specific inflammatory response.18 When used in the treatment of AKs, ingenol mebutate gel 0.05% may cause a mild to moderate localized inflammatory response (eg, erythema, flaking/scaling, crusting, vesiculation/pustulation, erosion/ulceration, edema).
Our case is a rare report of successful treatment of DSAP with ingenol mebutate gel 0.05%. We found that treatment with ingenol mebutate gel 0.05% resulted in clinical improvement of DSAP lesions with minimal discomfort and good cosmetic response. This 2-day regimen is easy to use and patient friendly, improving medication compliance in such a cumbersome disease. We hope this case suggests that ingenol mebutate gel 0.05% could be a useful treatment alternative for DSAP, but future clinical studies should be conducted.