Porokeratosis represents a heterogeneous group of hereditary and acquired disorders of clonal hyperproliferation of keratinocytes[5]. The characteristic ridge-like, keratotic border called "cornoid lamella" confirms the diagnosis of porokeratosis. Several clinical variants of porokeratosis have been described, all of which share this distinctive feature.
DSAP is the most common type of porokeratosis. It presents as keratotic papules with a well-demarcated elevated border, usually ranging from 3 to 10 mm in diameter. They are typically skin-colored to tan–brown to pink–red in color. DSAP usually occurs in the third or fourth decade of life, and patients frequently report a history of extensive exposure to ultraviolet radiation. For this reason, it usually happened in sun-exposed areas, most commonly the shins and extensor forearms. Lesions on our patient face are the typical DSAP. Although 15% of DSAP patients have facial lesions, exclusively facial DSAP is an unusual clinical presentation[6]. Ppt is an unusual psoriasiform variant of porokeratosis[7–9]. This type of porokeratosis typically presents with pruritic, red to brown, keratotic, or verrucous papules and plaques on the buttocks or genital skin[9]. Sometimes,the lesions could coalesce. Due to clinical similarities, Ppt are often mistaken for psoriasis[10] and chronic eczema. In this case, skin biopsy is a useful measure to identify the diagnosis. For our patient, the verrucous plaques on his scrotum, buttocks and limbs were diagnosed as Ppt according to the pathologic findings.
There are reports of coexistence of multiple types of porokeratosis in the same individual[2, 11–20]. Co-occurrence of DSAP with Ppt is rare. To our knowledge,this is the fifth case in published English literature to date [8, 21–23](Table 1).
The pathogenesis of porokeratosis is poorly understood. Risk factors include genetic susceptibility, exposure to ultraviolet radiation, and immunosuppression. Some studies have found mutations in the phosphomevalonate kinase pathway genes, namely MVD, MVK, PMVK, and FDPS in patients with porokeratosis[24–25]. At least one mutation in the mevalonate pathway genes was reported to be found in up to 98 percent of the familial and over 70 percent of sporadic porokeratosis cases[4]. Among the above five patients, two had genetic results. Jia-Mei Peng et al identified a novel MVK missense mutation (c.1039G > C, p.Gly347Arg) in the family with coexisting DSAP and Ppt[23]. In our patient's family, another MVK missense mutation (c.155G > A, p.Ser52Asn) was found. Although this mutation was reported to be benign before, we suggest it is a novel mutation associated with porokeratosis. Functional analysis of this mutation in vitro and in vivo should be performed in further study. Base on the two cases, we imagine that the mutation of phosphomevalonate kinase pathway genes, especially MVK gene may play an important role in the pathogenesis of DSAP coexisting with Ppt.
Patients with porokeratosis has a 7.5–10% risk of malignant transformation to squamous cell carcinoma or basal cell carcinoma[26]. Thus, clinical surveillance with regular skin examinations and patient education about the warning signs of skin cancer and sun protection are necessary aspects of the management of all patients with porokeratosis. However, some patients with function impairments or appearance requirements want to eradicate the lesions of porokeratosis. The treatment of porokeratosis is various, but the disease is easy to recur. We chose microwave knife to remove the hyperkeratotic plaques on patient's scrotum. The patient didn't have any function impairment caused by treatment and did not develop aggravation or recurrence during 6-years follow-up. This indicates that microwave knife is an effective and safe therapy for porokeratosis.