Scabies lesions on the penis.
Scabies is an infestation of the skin by a small mite which is transmitted by close physical contact. The mite makes a shallow burrow into the skin and lays eggs in this burrow. Two to four weeks after infection, red itching bumps or blisters occur. These bumps are an allergic reaction to the insects.
New insects hatch from the eggs and can be spread to other areas of the skin by scratching. Scabies most often involves the genitalia, waist-line, hands and wrists. Scabies almost never involves the face or back.
The disease is transmitted mainly by close body contact (including sexual activity).
Scabies is a contagious skin disease caused by the itch mite Sarcoptes scabiei.
Fertilised female mites burrow into the horny layer of the skin, advance some 2 mm each day, deposit eggs (2-3 per day for 10 days) and then die.
The transfer of the female mite requires close personal contact rather than transient personal contact.
Transmission can occur while:
Primary infection: symptoms will appear around 4 weeks after infestation.
In people who have previously had scabies, the symptoms will appear more rapidly, often within hours of infestation. (Due to increased sensitivity.)
The primary lesion, the burrow, is often difficult to see. It is a thread-like furrow or ridge 5-15 mm long. Burrows mostly occur on the medial and flexor (inside) surfaces of the wrists, the sides and webs of the fingers and sometimes around the nipples, penis, scrotum and buttocks. A vesicle (small blister) may appear at the end of a burrow.
In sexually acquired scabies the lesions are often confined to the lower trunk, thighs and genitals.
After about a month the lesions become papular (raised) and irritable, presumably through host sensitisation. Intense itching occurs, especially when the person becomes warm in bed, after exercise, a hot shower or bath.
Usually by the time people seek attention, the eruption has been scratched, burrows disrupted and secondary infection has occurred.
In males, penile or scrotal lumps can be the main or only complaint. The lumps, which may or may not itch, are seen as inflamed, reddish-brown, indurated nodules up to 12mm across. They are commonly seen on the penis, especially the glans, and on the scrotum. Careful searching may reveal scabetic lesions in some of the usual sites.
In people who shower frequently, the clinical signs of scabies may be minimal and not typical, and burrows especially difficult to find.
The prior use of topical applications containing steroids frequently masks the clinical features and hinders accurate diagnosis.
The distribution of the rash, the presence of burrows, the multiplicity of lesions, the intense irritation (especially when in bed or while warm) and the possible infestation of those in close personal contact make for a clinical diagnosis of scabies.
The diagnosis is confirmed by finding a whole acarus, an identifiable part or some eggs. Preferably using good natural light and a binocular loupe, a search should be made among the lesions for burrows. If the overlying epidermis is thin, the mite can sometimes be seen at the anterior end of a burrow. The burrow should be opened with a triangular, cutting-edge needle on the point of which the mite can be transferred to a glass slide for low power microscopic examination.
If no burrows can be found and a mite cannot be isolated, microscopy of skin scrapings taken over old burrows or papules, under a drop of potassium hydroxide 10% solution, will sometimes show parts of an acarus or some eggs.
Definitive diagnosis requires identification of the mite, eggs, larvae or faeces. Microscopic evidence of scabies should be obtained prior to initiating treatment.
Clinical diagnosis is made by observing typical lesions of wrists, fingers, axillae, penis or thighs or on eliciting the classic pattern of pruritus (at night; after hot shower/bath). If associated with exposure to an infected person, the index of suspicion should be high even if they have non-specific symptoms.
Immunosuppressed patients may present with Norwegian scabies. Large numbers of mites are present. The condition may not be pruritic. Extensive crusting may be seen.
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| Microscopic appearance of Sarcoptes scabiei, the parasite which causes scabies. |
Scabies lesions on the penis. |
permethrin 5% cream
Pay particular attention to the areas between the fingers and toes, under finger and toenails, wrists, armpits, genitals, buttocks and perianal area. It is usually helpful for a second person to assist with the application of cream to areas that are not easily accessible.
Pregnant and lactating patients
permethrin 5% cream
Although classified as B2, permethrin has been used in pregnancy and lactation.
An alternative although much less effective treatment is
sulfur 10% in sorbolene cream
or
crotamiton 10% lotion or cream
Apply to entire body from the neck down, at night for 2 consecutive nights. Wash off 24 hours after the second application.
Immunosuppressed and HIV positive patients
These patients may prove resistant to topical therapy. Referral to a Dermatology or Infectious Diseases specialist may be necessary for treatment with systemic ivermectin. Norwegian scabies may also need ivermectin treatment.
Nil. Patients should attend for results of any investigations performed.