Disseminated superfi cial actinic porokeratosis in a patient with generalized vitiligo: A case report

Porokeratosis is a keratinization skin disorder inherited as an autosomal dominant [1]. Disseminated superficial actinic porokeratosis (DSAP) is characterized by annular keratotic papules or plaques with a characteristic thread-like ridge and central atrophy that expand peripherally on sunexposed skin [2]. A cornoid lamella is a distinctive histopathological feature of all its types [3]. Certain stimuli can hasten the appearance of porokeratosis, such as immunosuppression, radiation therapy, artificial ultraviolet radiation, and chronic sun exposure [4,5]. Herein, we present the case of a patient with generalized vitiligo in whom DSAP occurred mainly in a sun-exposed depigmented patch.


INTRODUCTION
Porokeratosis is a keratinization skin disorder inherited as an autosomal dominant [1]. Disseminated superficial actinic porokeratosis (DSAP) is characterized by annular keratotic papules or plaques with a characteristic thread-like ridge and central atrophy that expand peripherally on sunexposed skin [2]. A cornoid lamella is a distinctive histopathological feature of all its types [3]. Certain stimuli can hasten the appearance of porokeratosis, such as immunosuppression, radiation therapy, artificial ultraviolet radiation, and chronic sun exposure [4,5]. Herein, we present the case of a patient with generalized vitiligo in whom DSAP occurred mainly in a sun-exposed depigmented patch.

CASE REPORT
A 65-year-old male farmer presented to our dermatology clinic complaining of pruritic and hyperkeratotic skin on the back of the hands and fingers persistent for five years prior. He had had generalized vitiligo for the last twenty years with no special treatment and no history of treatment with phototherapy or immunosuppressive drugs. Upon examination, the patient looked healthy, apart from the vitiligo, which involved more than 70% of the body, including the face, extremities, and trunk. There were multiple annular plaques with sharplydefined thin edges and atrophic centers distributed bilaterally and symmetrically on the back of both hands, limited mostly to the depigmented skin (Figs. 1a and 1b). A punch biopsy was taken to show a cornoid lamella, the characteristic histopathological feature of porokeratosis (Fig. 1c). General laboratory investigations were within normal limits. The patient was advised to avoid sun exposure, apply sunscreen regularly in the daytime and topical retinoid at night, and attend regular follow-ups. Informed consent was taken from the patient and approval for the study was obtained from our institution.

DISCUSSION
Vitiligo is a common acquired pigmentary disorder that results from loss of melanin-producing cells.
Melanin protects the skin from the harmful effects of the ultraviolet radiation (UVR) in sunlight [6]. UVR is the main factor in chronic sun exposure that induces nonmelanoma skin cancer (NMSC) by mutation of the TP53 gene [7]. Accordingly, vitiliginous skin is more vulnerable to these influences in comparison with normally pigmented skin. People with vitiligo show the same and even a lower incidence of cutaneous malignancies than other populations [1,8,9]. Some ascribe this to the increased expression of the tumorsuppressing gene TP53 in vitiligo [10,11]. Others point to the increase in certain cytokines and decrease in others acting as protective factors in vitiligo skin [10]. Photoadaptation, thickening of the stratum corneum, and the altered activity of the immune system are other explanations [11,12].
In contrast, there were several cases mentioned in the literature in which NMSC arose on depigmented skin, whether protected from the sun [2,11] or sunexposed [13,14]. In our case, DSAP developed on sun-exposed vitiliginous skin, and this may be the first such case published in the literature so far. In our case, there were no specific risk factors apart from chronic sun exposure and a 30-year absence of photoprotection.

CONCLUSION
Although sun-exposed vitiliginous skin may have a lower chance to become affected by NMSC for different reasons, certain factors may increase this possibility, such as the age of the patient, the duration and extent of the vitiligo, the chronicity of sun exposure, the presence of immunosuppression, and a family history of other genetic diseases.

Consent
The examination of the patient was conducted according to the principles of the Declaration of Helsinki.
The authors certify that they have obtained all appropriate patient consent forms, in which the patients gave their consent for images and other clinical information to be included in the journal. The patients understand that their names and initials will not be published and due effort will be made to conceal their identity, but that anonymity cannot be guaranteed.