Porokeratosis

Porokeratosis is a group of inherited skin disorders characterized by abnormal keratinization, leading to the formation of distinct lesions. The hallmark clinical presentation is a well-demarcated papule or plaque with a raised, slightly scaly border and a central depressed area that may be slightly atrophic or hyperkeratotic. The lesions can occur anywhere on the body, but are most commonly found on the extremities. They are typically asymptomatic, although some individuals may experience mild itching or burning.

There are several clinical variants of porokeratosis, distinguished by their morphology and distribution. Porokeratosis of Mibelli is the most common type, presenting as annular or linear plaques. Disseminated superficial actinic porokeratosis (DSAP) is prevalent in sun-exposed areas, particularly in fair-skinned individuals, and manifests as numerous small, scattered lesions. Other variants include linear porokeratosis, punctate porokeratosis, and porokeratosis palmaris et plantaris disseminata.

The underlying cause of porokeratosis is a defect in keratinocyte differentiation and proliferation, which leads to the formation of a characteristic histological finding known as the "cornoid lamella." This is a vertical column of parakeratotic cells, representing a stack of abnormal keratinocytes, overlying a depressed stratum granulosum. While the exact genetic mutations are still being investigated, several genes have been implicated in the pathogenesis of porokeratosis.

Diagnosis is primarily based on clinical appearance and confirmed by skin biopsy. Treatment is often challenging and focuses on managing the cosmetic concerns and preventing potential malignant transformation. Options include topical retinoids, cryotherapy, 5-fluorouracil, and surgical excision for isolated lesions. Sun protection is crucial, especially for individuals with DSAP, to minimize the development of new lesions. Malignant transformation, though uncommon, can occur within porokeratosis lesions, most frequently developing into squamous cell carcinoma. Regular dermatological follow-up is recommended for monitoring.