Porokeratoses: an update on pathogenesis and treatment.

Porokeratoses (PK) are a group of uncommon dermatoses characterized by abnormal epidermal differentiation due to a disorder of the mevalonate metabolic pathway. Several clinical subtypes exist that can be associated with the same patient or affect different patients within a family and could, therefore, be different expressions of one disease. All PK subtypes share a common histopathologic finding, the cornoid lamella, a vertical stack of parakeratotic corneocytes embedded in an orthokeratotic horny layer. PK often affects immunosuppressed patients, in whom the course may parallel the level of immunosuppression. The pathogenesis of PK, which had long remained mysterious, has been recently unraveled after discovering pathogenic variants of genes involved in the mevalonate metabolic pathway. The disease is due to germline pathogenic variants of genes of this pathway but requires a second-hit event to manifest; therefore, PK is considered a dominantly inherited but recessively expressed condition. The prognosis of PK is usually favorable, even though the lesions progress to keratinocyte carcinomas in 7%-16% of patients. The treatment of PK was based on physical (ablative) procedures and various (topical or systemic) treatments, whose efficacy is nevertheless inconsistent and often temporary. The discovery of the metabolic pathway involved in the pathogenesis of PK paved the way for the elaboration of new topical treatments (combination of statins and cholesterol), which are more regularly efficacious compared with older treatments, even though the management of some patients with PK may still be challenging.