Porokeratoses: an update of clinical, aetiopathogenic and therapeutic features.

Porokeratoses represent a group of uncommon, acquired or hereditary dermatoses, due to a keratinization disorder whose origin is still unclear; they could be due to the expansion of a clone of abnormal epidermal keratinocytes. Several clinical forms exist, of which the most common is disseminated superficial actinic porokeratosis; other forms include Mibelli, disseminated superficial, linear, palmoplantaris punctata and palmaris, plantaris et disseminata. These may coexist in the same patient or in different members of the same family. Porokeratoses manifest clinically with annular or linear, well-circumscribed keratotic plaques and share a common histological hallmark, the cornoid lamella, a vertical stack of parakeratotic corneocytes within the horny layer resting on a shallow depression of the underlying epidermis. Porokeratoses may be seen in the setting of various immunodeficiencies, namely in organ-transplant recipients, in whom the course of the disease may parallel the degree of immunosuppression. The overall prognosis of porokeratoses is favourable but is shadowed by the possibility of malignant transformation of the lesions (usually into squamous cell carcinoma); this happens in less than 10% of cases but may prove fatal. Although several surgical or medical (local or systemic) treatments have been tried, none of them has shown consistent and long-term efficacy.