The patient presenting with genital irritation should be asked the following:
- Exactly where is the irritation - penis, scrotum, toward the entrance of the vagina, on the labia majora, above the genitalia in the public area?
- Is there anything to see, such as a rash, warts, or public lice?
- Is there irritation elsewhere on the body?
The following are the commonest causes of genital irritation:
- Dermatoses - dermatitis, lichen simplex, lichen planus, lichen sclerosus, etc.
- Infection - candidiasis, early genital herpes (preulcerative stage), HPV infection (warts or VIN ), trichomoniasis, pubic lice.
These conditions are mostly covered in other sections (see Chapters 8 and 16). This chapter will focus on the two common parasitic infections: pubic lice and scabies.
19.1 PUBIC LICE (“CRABS” OR PEDICULOSIS)
The pubic louse (Phthirus pubis) may spread to any hairy part of the body with the exception of the scalp and eyebrows. Very occasionally the eyelashes may be involved. Transmission is by body contact although toilet seats and shared clothing have been implicated in a small number of cases. Pubic lice are very slow movers and live for only a day away from the host.
Irritation is the commonest presenting symptom and the severity will depend on the level of hypersensitivity to mite antigen. In a previously unexposed individual, symptoms may take up to 5 days to occur. Excessive scratching can sometimes lead to excoriation and secondary infection. A large infestation resulting in multiple bites over a short period of time may cause mild fever and general malaise.
A careful search for eggs (nits) and lice may be required in milder infections. To the uninitiated, lice resemble "freckles" or small brown "scabs" (Figure 19.1). Pubic lice move on average a maximum of only 10 cm a day so it is unusual to see any activity during a 5-minute consultation.
Clothing should be laundered in hot water or by dry cleaning.
The most widely used pediculosides are 0.5% malathion lotion, 1% permethrin cream, 0.2% phenothrin, and 0.5% or 1% carbaryl. Preparations are usually rubbed into the hairs and washed off 12 hours later. Although a second treatment is recommended after 1 week to kill any lice emerging from surviving eggs, the presence of eggs does not signify treatment failure. The possibility of itching persisting after successful treatment should be mentioned to the patient. If this proves a problem, consider using topical hydrocortisone or an oral antihistamine, such as one of the sedative preparations, at night.
Figure 19.1. Pubic lice and nits (seen as tiny brown ‘marks') - may be difficult to visualise in mild infections
Shaving the hair is unnecessary and may aggravate the irritation. Sexual contacts should be assessed and treated as appropriate. An infestation affecting the eyelashes may be effectively treated with permethrin or by applying Vaseline gently to the lashes.
The scabies mite (Sarcoptes scabei) is much smaller than the pubic louse and is only just visible to the naked eye. Transmission is by close personal contact and occasionally by wearing infected clothes. Although scabies is seen in school-age children, transmission within schools is uncommon. Outbreaks occasionally occur in nursing homes, hospitals, and other institutions. The incubation period for a first attack is up to 8 weeks with subsequent attacks producing symptoms within a few days because of previous sensitization.
Irritation tends to be generalized, sparing the head, and is worse at night.
Genital lesions are generally found only in men and appear as nodules on the penile shaft and scrotum. There is usually evidence of scabies elsewhere, particularly favored sites being the finger webs and sides of the fingers, flexor surfaces of the wrists, extensor surfaces of the elbows, anterior axillary folds, umbilicus, nipples, and buttock creases.
Classical lesions include the following:
• Short, wavy, dirty appearing burrows
• Small, erythematous, eczematous papules
• Small nodules (penis, scrotum) (Figure 19.2).
The scalp, face, and neck are spared in adults. Scratch marks are frequently seen and secondary eczematization and infection may mask the other features and make diagnosis rather more difficult.
Scabies is often diagnosed purely on clinical grounds: intense irritation, especially at night, characteristic lesions, and similar complaints in household members or sexual partners. Where possible, however, an attempt should be made to confirm the diagnosis which involves identifying the mite, eggs, or larvae under the microscope. First place a drop or two of Indian ink on to a suspected burrow and remove any excess with an alcohol wipe. This helps to "highlight" the burrow which should then be scraped gently with a scalpel blade and the material obtained transferred to a microscope slide. Apply a cover slip and examine with a microscope using low-power magnification.
Figure 19.2. Scabetic nodules
(1) All household members and sexual partners should be treated: they may remain asymptomatic for up to 8 weeks and during that time spread the disease unknowingly.
(2) All patients should be warned to expect continued irritation for as long as 3 months after successful treatment.
(3) Warn patients against overtreatment that can cause an irritant dermatitis.
(4) Lotions are easier to apply than creams.
(5) The lotion should be applied to all of the skin from the neck downward with particular attention to palms, soles, interdigital spaces, and genitals. This is most easily performed with a 3-5 cm paint brush and help is usually required to reach the more distant areas.
(6) Bathing before the lotion is applied is unnecessary and may increase systemic absorption of the scabicide.
(7) Antihistamines and crotamiton cream may help to relieve the irritation.
(8) Re-infection from bedlinen and clothing is no longer considered a risk.
The treatments available include 0.5% malathion lotion and 5% permethrin cream. These should be washed off after 24 hours.