Porokeratosis
The hard protruding edges are characteristic.
References
Porokeratosis is an uncommon dermatologic disorder. It is a disorder of keratinization that presents with keratotic papules or annular plaques with an elevated border. It has a distinct histologic hallmark of cornoid lamella, which is a column of tightly fitted parakeratotic cells in the upper epidermis. There are multiple clinical variants of porokeratosis, including disseminated superficial actinic porokeratosis, classical porokeratosis of Mibelli, porokeratosis palmaris plantaris et disseminatum, and linear porokeratosis. Porokeratosis is a precancerous lesion that can undergo malignant transformation. Evaluation of porokeratosis is best with a biopsy of the elevated border. There are no standard guidelines for treatment.
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. The eruptive form of porokeratosis is associated with malignancy, immunosuppression, and a proinflammatory state. Risk factors for porokeratosis include genetics, immunosuppression, and ultraviolet light. The lesions in disseminated superficial actinic porokeratosis start as pink to brown papules and macules with a raised border in sun-exposed areas that can be asymptomatic or slightly pruritic. There are many options for the 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 precancerous. There is a 7.5 to 10% risk of malignant transformation to squamous cell carcinoma or basal cell carcinoma.
A 52-year-old man with no past medical history presented with an asymptomatic annular atrophic patch on the distal portion of the fourth toe of 2 years’ duration. The lesion began as a small keratotic papule that gradually enlarged centrifugally. He had received multiple treatments including cryotherapy, topical corticosteroids, antifungals, and antibiotics without improvement. Dermoscopic examination revealed a scaly atrophic erythematous central area with a sharply demarcated peripheral hyperkeratotic structure. A skin biopsy of the edge of the lesion revealed a cornoid lamella with a column of parakeratotic cells extending from an invagination of the epidermis with absence of granular layer. The clinicopathologic correlation was consistent with porokeratosis of Mibelli.
Often a biopsy is performed because it can look similar to actinic keratosis or squamous cell carcinoma.