Skin Disorders
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Infestations of the Skin

Definition

Scabies: Infestation of the epidermis by Sarcoptes scabiei, a microscopic insect like mite that burrows in the skin and reproduces.

Pediculosis (lice): Infestation by Pediculus humanus capitis (head louse); Pediculus humana corporis (body louse/cootie), or Phthirus pubis (pubic louse/crab).

History

Symptoms Scabies: Dry, red bumps with intense itch, especially at night. Affects the arms, legs, and trunk.

Pediculosis (lice): The patient has bugs in his or her hairs. Complain of itching, with or without red-dots rash on head, body, or groin.

Age

Scabies: Any but mostly children. Pediculosis (lice): Any, but mostly school age.

Onset

Scabies: Acute.

Pediculosis (lice): Acute with symptoms, or slow with another person noticing the condition.

Duration

Scabies: Weeks to months until treated. Pediculosis (lice): Weeks to months.

Intensity

Scabies: From a few papules around hands or fingers to widespread pruritic papules of extremities and trunk. Periods of exacerbation with calm but progressive symptoms.

Pediculosis (lice): Many mites, nits, papules, bites or no symptoms or signs.

Aggravating Factors

Scabies: Scratch, heat.

Pediculosis (lice): Poor hygiene, contact with infested person or use of or contact with fomite.

Alleviating Factors

Scabies: Treatment including antipruritics.

Pediculosis (lice): Fastidious cleansing and appropriate treatment.

Associated Factors

Scabies: Friend or family member may have similar, same complaints. Blacks are more resistant.

Pediculosis (lice): Rare in Blacks; common in Pan-Americans, Caribbean natives, and Caucasians. Also found in American Indians and Orientals.

Physical Examination

General

Scabies: Red, dry papulovesicles that begin about the hands, wrists, ankles, or lower legs with steady spread to wide periaxillary shoulder area, around the waist, in the groin, and on the buttock. May note burrows or dry short track lines with terminal papule. The mite is in the papule. The female nipple and the male penis are a common site of infestation with larger papules. Rare on face and the face is the last area affected in children. Significant excoriation common. Purulence and inflammation is common with seconday infection.

Pediculosis (lice): Head lice mites have elongated insect looking bodies, are small but visible, and move on the scalp and in the hair very quickly. Most common sites are behind the ears and over the occiput, but can occur anywhere on scalp in the hair. Ova attach as white nits to the base of hair shafts. Most common in girls and women. The body louse has a larger elongated body, moves slower, and is found usually on the trunk

and thighs of men. Nits attach to clothing seams, not hair. Bites occur as red papules and weals, lead to excoriations and some times pyodermas. The pubic louse has a wider body and looks like a small crab. They are light, almost translucent and found in the pubic area, but may be in axillary hair, eyebrows, or eyelashes. Tan nits are readily visible on close inspection. Also leave steel gray spots on chest, abdomen, and thighs (maculae caeruleae).

Pathophysiology

Scabies: Acquired by direct contact. The S. scabiei mite secretes enzymes that dissolve stratum corneum cells and burrows under the stratum corneum and into the epidermis to lay eggs and secrete waste. The mite and its products, (ova, egg casings, feces, or scybala) are sensitizing and lead to the intense pruritis and reactive papulovesicles.

Pediculosis (lice): Infestation is by direct contact with use of contaminated combs, brushes, clothes, beds, hats, etc. Lice feed by biting the skin and sucking blood. This infestation may lead to allergic reactions such as eczemas and urticarias. They cement, with secretions, their eggs to hair shafts as nits or to clothing as body louse. The body louse may vector epidemic typhus fever, relapsing fever, or trench fever to its host. Head and pubic lice do not vector disease.

Diagnostic Studies

Laboratory: Not applicable.

Radiology: Not applicable.

Other

Scabies: KOH preparation or oil: Viewed under the microscope, mites, mite parts, eggs, or feces is diagnostic but not always demonstrable.

Skin scraping: Of papulovesicles and/or burrows and tracks and/or recover scrapings from under nails and smear on slide.

Biopsy: Rarely necessary.

Pediculosis (lice): Not applicable.

Differential Diagnosis

Traumatic: Not applicable.

Infectious

Scabies: Folliculitis: Not nearly as pruritic and dry. No burrows or tracks, different locations more typical (except buttocks).

Pediculosis (lice): Not applicable.

Metabolic: Not applicable.

Neoplastic: Not applicable.

Vascular: Not applicable.

Congenital: Not applicable.

Acquired

Scabies: Not applicable.

Pediculosis (lice): Fleas: Do not stay on the body long, but bite 2 to 4 times in an area and move on and off.

Chiggers: Bite several times in infested area and leave feces dots in hair or skin. Involve extremities and or trunk. Any other mites bite and run leaving no nits or tracks or feces.

Treatment

Scabies: Lindane 1 percent lotion applied 2 nights in a row for 12 hours, then rinsed and repeated one time a week thereafter. Should be applied everywhere except the face. From the jaws downward, Eurax cream applied overnight for 3 nights and repeated the following week. (Safest for infants and pregnant patients.) Lindane can be used in infants but only for 2 hours and care to avoid putting fingers in mouth. Elimite cream applied once overnight and may be repeated a week later, has had some success and is safe.

Pediculosis (lice): Must treat all contacts and fomites. Lindane 1 percent shampoo for head, lotion or creams for rest of body. Protect eyes, nose, mouth, and all body orifices. Apply liberally on the head and chest for capitis, entire body for other infestations. Leave creams or lotions on body overnight 10 to 12 hours then rinse and repeat a week later. Nits should be picked off or combed out with special combs. Can be softened with vinegar or 3 percent acetic acid solution. Clothing and bedding should be hot laundered and/or isolated in plastic bag 3 weeks or more. Furniture should be sprayed with pyrethrins or permethrins with RC spray. Carpets, rugs, chairs, and sofas should be vacuumed. Fomites such as brushes, combs, etc., should be isolated 3 weeks or more and super heated or frozen in freezer for 1 week. Treat all contacts concurrently. Antipruritics may be needed and helpful (e.g., HC 1 percent with menthol 1 percent cream or lotion). Antihistamines, analgesics, and systemic corticosteroids may be used judiciously. OTC pyrethrin preparations: RID, A200, RC, or permethrins such as Nix may be effective.

Pediatric Considerations

Scabies: Abuse of lindane can cause neurologic damage.

pediculosis (lice): Use lindane for only 2 to 3 hours in infants. Infants should be held or monitored to prevent them from placing fingers in the mouth.

Obstetrical Considerations

Scabies: Lindane can be used but with strict obedience to directions. Best to use Eurax.

Pediculosis (lice): Great care and monitoring using any of the topical preparations as pediculicides.

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