Genital Porokeratosis: A Distinct Clinical Variant?

Sir,

Porokeratosis (PK) is a primary disorder of epidermal keratinization which presents with typical annular lesions with a hyperkeratotic raised border. The localized variants include classic PK of Mibelli, linear PK, and punctate PK.[1] PK of the genitalia is a rare entity with most cases reported in the 4th-5th decade. It has traditionally been included within porokeratosis of Mibelli or as a plaque form, although most published cases share some differential characteristics that suggest defining genital PK as a distinct clinical variant.[2] A 22-year-old married man presented with multiple pruritic lesions over scrotum since 4 years. They began as lentil sized lesions 4 years back and progressed in size and number spreading to involve the penis since 6 months. There was no response to various topical medicaments including steroids and antifungals. There was no family history of similar complaints and no history suggestive of immunosuppression. Cutaneous examination revealed multiple well-defined skin colored scaly annular plaques approximately 6 to 14 mm in diameter present over the scrotum and shaft of penis with a slightly depressed center surrounded by a peripheral hyperkeratotic ridge [Figure 1]. On stretching the skin the peripheral ridge revealed a circumferential furrow which was further delineated by performing the ink test using gentian violet stain [Figure 2]. Examination of the perianal, gluteal cleft and groin was within normal limits. With the differential diagnosis of PK, lichen planus, granuloma annulare and psoriasis a punch biopsy was taken from the raised peripheral edge. Routine investigations revealed no abnormality. Hematoxylin and eosin staining of the biopsy specimen showed the presence of cornoid lamella [Figure 3]. A diagnosis of porokeratosis was established.[3] The patient was started on capsule isotretinoin 20 mg once a day and twice daily application of fluticasone propionate cream. At 6 weeks follow up the pruritus had decreased and there was slight flattening of the annular plaques [Figure 4]. Although PK can nearly involve any area of the body, genital PK is considered extremely rare. Genital PK has traditionally been included within porokeratosis of Mibelli and its true incidence is still undetermined. Repeated trauma (friction or scratching) might explain a part of pathogenesis.[1] Chen et al.[1] compiled all 11 published cases of porokeratosis confined to the genitalia and found all cases were described only in men except for 1 case reported in the natal cleft of a female. Three cases were associated with itching, one case had decreased CD4/CD8 without HIV and no malignant transformation was found In any of the reported cases. The authors postulated that these aforementioned features differentiate PK localized to genitalia from PKM.[1] Several therapeutic options have been described, such as cryotherapy, CO2 laser therapy, oral retinoids, and topical treatment with vitamin D3 analogues, keratolytic agents, 5-fluorouracil under occlusion, and, more recently, imiquimod under occlusion, and photodynamic therapy, with variable results.[2] The presence of multiple scaly annular pruritic plaques localized to the genitalia in a young male made a diagnosis of papulosquamous disorders a likely possibility. However, a positive ink test with presence of characteristic cornoid lamella on histopathology confirmed a diagnosis of porokeratosis. We report this case to suggest consideration of genital porokeratosis as a distinct clinical entity and its inclusion in the list of differential diagnosis of annular plaques localized to the genitalia. Additionally, due to paucity of data regarding the risk of malignant transformation in this entity, regularfollow up of these patients is warranted.

Figure 1

Multiple annular plaques over the penis and scrotum with slightly atrophic center and a raised border

Figure 2

Positive ink test with retention of the gentian violet dye in the thread-like border aiding in its clear delineation

Figure 3

Hematoxylin and Eosin staining (×100) revealed the presence of a keratin-filled invagination of the epidermis. The center of this keratin-filled invagination had a parakeratotic column and the epidermis beneath this column revealed absence of the granular layer and irregular arrangement of keratinocytes suggestive of a cornoid lamella

Figure 4

The plaques on the penile shaft and scrotum give a smooth and flattened appearance after 6 weeks of treatment