Porokeratosis is a disorder of epidermal keratinization which is characterized by the presence of cornoid lamellae. Since the original description of the plaque form of Mibelli, various types of porokeratosis have been reported.

The purposes of this study were aimed at evaluating the clinical and biological features of porokeraosis.

The hospital charts and slides of 29 patients with porokeratosis were reviewed. Only the cases showing characteristic cornoid lamellae by histopathological examinations were included.

Female patients outnumbered the male ones (M:F = 1:2.2). Ages of the onset of porokeratosis varied from infancy to 68 years. Disseminated superficial actinic porokeratosis (DSAP) was the predominant type (22 cases). The Mibelli type was seen in 3 cases and the linear type in 4 cases. Only one case had a family history of porokeratosis. Two patients had complained of pruritus in the lesions, which were the DSAP and linear type, respectively. In that linear type, squamous cell carcinoma developed. Eight patients had other associated diseases. Although 6 patients were treated with CO₂ laser, topical isotretinoin or cryotherapy, the lesions tended to recur, persist or even progress.

Porokeratosis showed various clinical features. DSAP was the predominant type. Two patients complained of itching of the lesions, which were the DSAP and linear types, respeciively. Within that linear type, squamous cell carcinoma developed. We speculate that pruritus might be an ominous sign of malignant transformation of the porokeratosis. We suggest that the Mibelli type and linear type of porokeratosis should be either excised or destroyed, or in widespread cases close follow-up should be mandatory.