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.
