INTRODUCTION
Porokeratosis is a rare group of acquired or hereditary dermatoses characterized by pruritic, linear, or annular plaques with a keratotic border.1,2 Although the pathophysiology remains unclear, the development of porokeratosis is thought to result from abnormal expansion of epidermal keratocytes.3-5 Disease occurrence has been linked to multiple etiologies including ultraviolet light exposure, inflammatory states, immunosuppression (ie, transplantation patients), malignancy, repeated minor frictional trauma (ie, tight clothing), and genetics.1,6,7 Six main variants of porokeratosis exist: linear subtype, punctate subtype, disseminated superficial actinic porokeratosis (DSAP), porokeratosis of Mibelli (PM), porokeratosis palmaris et plantaris disseminata (PPPD), and porokeratosis eccrine ostial and dermal duct nevus.8 Recently, a familial form of DSAP has been identified through mutations in the mevalonate kinase gene (MVK) on chromosome 12q24 responsible for production of intermediate products in the cholesterol synthesis pathway. The MVK gene codes the enzyme mevalonate kinase which plays an integral role in UV light protection.7,9 This discovery prompted the exploitation of the statin class of medications by targeting the inhibition of the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase in the treatment of DSAP.
Porokeratosis most commonly afflicts the trunk and extremities but can also appear on the face and genitourinary regions.10 Although the onset of disease can occur at any age, presentation during the fifth decade of life is most common. It affects both sexes evenly.11 DSAP is the most common porokeratosis, with greater cutaneous involvement than other variants. Unlike other porokeratosis, DSAP presents earlier, within the third or fourth decade of life with a slight predominance in females.12 Skin lesions range from asymptomatic to pruritic circular pink to brown macules, papules, or plaques surrounded by a raised border. DSAP most commonly affects the forearms, shoulders, legs, and back with bilateral distribution; face involvement is rare, and palms and soles are typically spared.13,14 These lesions are precancerous, with a 7.5-10% risk of malignant transformation to squamous cell carcinoma (SCC) or basal cell carcinoma (BCC).15,16 Linear porokeratosis (LP) and giant keratosis are the variants most susceptible to malignant transformation.17 Diagnosis can be made clinically, and confirmed with skin biopsy. Pathognomonic histopathologic features of porokeratosis include cornoid lamellation, with an absent granular layer and dyskeratotic cells in the upper spinous zone.6,10,11
Porokeratosis most commonly afflicts the trunk and extremities but can also appear on the face and genitourinary regions.10 Although the onset of disease can occur at any age, presentation during the fifth decade of life is most common. It affects both sexes evenly.11 DSAP is the most common porokeratosis, with greater cutaneous involvement than other variants. Unlike other porokeratosis, DSAP presents earlier, within the third or fourth decade of life with a slight predominance in females.12 Skin lesions range from asymptomatic to pruritic circular pink to brown macules, papules, or plaques surrounded by a raised border. DSAP most commonly affects the forearms, shoulders, legs, and back with bilateral distribution; face involvement is rare, and palms and soles are typically spared.13,14 These lesions are precancerous, with a 7.5-10% risk of malignant transformation to squamous cell carcinoma (SCC) or basal cell carcinoma (BCC).15,16 Linear porokeratosis (LP) and giant keratosis are the variants most susceptible to malignant transformation.17 Diagnosis can be made clinically, and confirmed with skin biopsy. Pathognomonic histopathologic features of porokeratosis include cornoid lamellation, with an absent granular layer and dyskeratotic cells in the upper spinous zone.6,10,11
