SCROTAL SKIN DISEASES II: SCABIES AND LICE
Scabies is a contagious, parasitic skin disorder caused by the mite Sarcoptes scabiei. Mites are small, eight-legged parasites (in contrast to six-legged insects), 1/3 mm long, that burrow into the skin and that are especially active at night, producing intense nocturnal itching. Furrows are readily visible on the scrotum, and a tiny burrow can be detected at the point where the skin has been invaded. The furrows vary in length and coloration and are usually curved or arciform, resembling a small beaded or dotted thread. At the distal, closed end of the tortuous channel, a small vesicle develops where the mite is lodged. Scraping the vesicle usually produces the mite and eggs that can be visualized in 10% NaOH solution. The vesicles quickly transform into papules, pustules, incrustations, and excoriations that obscure the burrows. Once secondary excoriation and pustules develop, the original skin lesions are more difﬁcult to recognize. In children, scabies is frequently complicated by impetigo of the buttocks. Skin-to-skin contact is the most common mode of spread and human scabies is not obtained from animal contact. Scabies is curable with permethrin, crotamiton, or lindane creams.
Pediculosis pubis is a result of infestation by the crab louse (Pthirus pubis). This ectoparasite feeds exclusively on blood and has an oral appendage that produces a skin lesion by suction. Unlike the body louse that lives in clothing, the crab louse resides on hairy body parts: in the genitalia, this louse attaches to pubic hair with its head buried in the hair follicle. Usually acquired during sexual contact, these lice rarely produce large skin lesions, and most commonly cause scratching. Because these organisms are most often spread through close or intimate contact, pediculosis is classiﬁed as a sexually transmitted disease (STD) that is not prevented with condom use. The skin may reveal a “bitten” appearance, showing small red points that may develop into papules. Scratching leads to excoriation, bleeding, and incrustation and a brownish discoloration of the skin. In addition, blue spots or macula cerulea up to 0.5 cm in diameter can occur on the skin as a result of the bite of the louse and is likely a consequence of a reaction between the louse saliva and the host blood. These blue spots do not disappear under pressure and are characteristic of pediculosis.
A careful search among the pubic hairs for nits, nymphs, and adults should be made in cases of pruritus. Lice and nits can be removed either with forceps or by cutting the infested hair with scissors and then examined with a microscope. Crab lice are also treated and killed with permethrin or lindane creams. A second treatment is recommended 10 days after the ﬁrst. It is also crucial that all bed linens be changed and put into well-sealed plastic bags for 2 weeks before washing to destroy the lice eggs that may be a source of reinfestation.