Disseminated superficial actinic porokeratosis (DSAP) is a disease of disordered keratinization. Disseminated superficial actinic porokeratosis is one of six variants of porokeratosis. It has more extensive involvement than most other variants. These other variants include linear porokeratosis, porokeratosis of Mibelli, punctate porokeratosis, porokeratosis palmaris et plantaris disseminata, and disseminated superficial porokeratosis. Porokeratosis ptychotropica, facial porokeratosis, giant porokeratosis, hypertrophic verrucous porokeratosis, reticulate porokeratosis and eruptive pruritic papular porokeratosis are other rare variants. The eruptive form of porokeratosis is associated with malignancy, immunosuppression, and proinflammatory state. The lesions appear all over the body. A feature that is seen in all of these variants is the cornoid lamella. It is seen on histology as a column of parakeratotic cells and is characterized by a raised ridge circumscribing the porokeratotic lesions. Risk factors for porokeratosis include genetics, immunosuppression, and ultraviolet light. The lesions in disseminated superficial actinic porokeratosis start out as pink to brown papules and macules with a raised border in sun-exposed areas that can be asymptomatic or be slightly pruritic. There are many options for treatment of disseminated superficial actinic porokeratosis including topical diclofenac, photodynamic therapy (PDT), 5-fluorouracil (5-FU), imiquimod, vitamin D analogs, retinoids, and lasers. These lesions are considered pre-cancerous. There is a 7.5% to 10% risk of malignant transformation to squamous cell carcinoma or basal cell carcinoma.
Genetics, ultraviolet radiation, trauma, infection, immunosuppression (including posttransplant) are causes of porokeratosis. There is a form of disseminated superficial actinic porokeratosis that is familial. Familial DSAP has an autosomal dominant inheritance pattern with incomplete penetrance. Mutation in mevalonate kinase gene (MVK) on chromosome 12q24 were seen in patients with disseminated superficial actinic porokeratosis. MVK gene codes for mevalonate kinase, an enzyme that is part of the cholesterol synthesis pathway, that offers protection against ultraviolet light-induced cell death. Disseminated superficial actinic porokeratosis has a high incidence and is the most common form of porokeratosis. The possibility for malignant transformation is due to overexpression of p53 and is seen more commonly in lesions that have been present for a long time, larger lesions, lesions in the elderly, or lesions in patients that are immunocompromised.
There is a slight female predominance. It is seen more commonly in the 30s and 40s.
Skin biopsy should be done to include the border of the lesion. A column of parakeratotic cells is seen correlating to the raised border. This column is called the cornoid lamella. The granular layer underneath this column can be thin or not present. Spongiosis can be present.
Lesions appear as asymptomatic or pruritic erythematous or brown circular macules, papules, or plaques with a raised hyperkeratotic border surrounding the lesions and an atrophic and hypopigmented center. It occurs bilaterally and symmetrically. Lesions most commonly present in the third or fourth decade and occur in areas exposed to sunlight. The legs, forearms, shoulders, and back are the areas most commonly affected. The face can rarely be involved. The palms and soles are spared. Disseminated superficial actinic porokeratosis usually worsens when it is exposed to sunlight and pruritus can intensify.
Disseminated superficial actinic porokeratosis can be diagnosed clinically due to the characteristic appearance of the lesions. A skin biopsy can be performed if there is doubt. Dermoscopy can be a useful tool for evaluating disseminated superficial actinic porokeratosis.
Nicola et al. proposed dermoscopic features seen in porokeratotic lesions.
Treatment options include the following.
Diclofenac is a NSAID that inhibits COX-2. The medication was approved for actinic keratosis and has been used to treat disseminated superficial actinic porokeratosis with variable results. It has a good safety profile.
Ingenol mebutate is used in the treatment of actinic keratosis and can be used for disseminated superficial actinic porokeratosis lesions. It can help with the hyperkeratosis but not the atrophy or hypopigmentation.
Topical Vitamin D analog
Vitamin D3 analogs have shown good responses after being used for 6 to 8 weeks. Vitamin D3 analogs are known to induce the transcription of genes that are responsible for differentiation and proliferation of the keratinocytes.
5-FU inhibits thymidylate synthase and stops DNA synthesis, therefore, inhibiting fast proliferating cells. Its use results in a very severe and robust inflammatory reaction in some patients including erythema, ulcerations, and dermatitis. The clinical response is usually temporary.
Imiquimod works by recruiting the body's immune cells through activation of toll-like receptors 7 and 8 and the induction of cytokines. It has been used mostly for porokeratosis of Mibelli and porokeratosis palmaris et plantaris. It can induce an inflammatory response similar to 5-FU.
Photodynamic therapy has been used to treat actinic keratosis, basal cell carcinoma, and squamous cell carcinoma in situ. A photosensitizer is applied that gets uptaken by atypical keratinocytes. The photosensitizers used are 5-aminolevulinic acid (ALA) and methyl aminolevulinate (MAL). The atypical keratinocytes are destroyed when a light is applied because the photosensitizers generate reactive oxygen species. Some studies show that MAL might be better than ALA because it is more lipophilic.
Retinoids are vitamin A derivatives and are used in disorders where there is abnormal keratinocyte proliferation. Topical retinoids are preferred over systemic retinoids. Systemic retinoids have more side effects and are teratogenic. Relapse is common.
Cryotherapy and Other
Cryotherapy, excision, curettage, and dermabrasion have been shown to have some good response. It is however limited and is not used for extensive disease. Cryotherapy leaves a scar and recurrence is common.
Carbon dioxide (CO2), Q-switched ruby (QSRL), Neodymium:yttrium-aluminum-garnet (Nd:YAG), fractional photothermolysis (FP) lasers, and Grenz ray have been used to treat Disseminated superficial actinic porokeratosis. The carbon dioxide laser uses pulsed or scattered infrared light with wavelengths between 9.4 micrometers and 10.6 micrometers and works on the water inside cells. Vaporization of the liquid causes tissue destruction. Its use can leave hyperpigmentation. QSRL uses melanin as its target. It reduces hyperpigmentation but does not destroy the cornoid lamella. It has greater penetration than Nd:YAG. Nd:YAG laser is used at 532 nm for pigmented lesions. It removes the superficial papillary dermis. It was shown to decrease the hyperpigmentation and obliteration of the cornoid lamella. FP induces small zones of thermal necrosis that doesn't create too much damage, redness, or pain and allows for faster healing. Grenz ray uses electromagnetic radiation like x-rays. It inhibits proliferation by inhibiting DNA synthesis.
Medications that suppress the immune response, such as topical corticosteroids, are not usually effective because disseminated superficial actinic porokeratosis is not an inflammatory disease but using these medications can help with the associated pruritus.