Scabies

Key Points
Skin condition which may affect various areas of the body. Classic distribution includes the finger webs, wrists, underarms, and groin.
Caused by an infestation of mites
Consists of irregular tracks at the site of infestation, accompanied by an itchy, red papular rash on the torso and limbs

Scabies is a skin condition which may affect various parts of the body. The condition consists of the formation of irregular grey tracks which are the burrows of mites, often in areas with skin folds, on the wrists, and soles of the feet, which is followed by the formation of an itchy, red papular rash on the torso and limbs. The condition is also accompanied by moderate to severe itching, which worsens at night. Additionally, itchy nodules may develop in the armpits or groin in some cases and may persist for weeks after the infestation has be resolved. Affected infants may also experience acropustulosis, the formation of blisters on the palms and soles. The condition also carries with it an increased risk of secondary infection.

Crusted scabies occurs in patients are unable to scratch or are immunosuppressed. The number of mites is drastically larger, and typically consists of a very scaly rash, which may affect much of the body including the scalp and the palms and soles. The condition typically affects those persons whose immune systems are compromised, elderly persons, or those with neurological or mental disorders. It is most frequently seen in nursing home settings.

Scabies is caused by an infestation of the human itch mites, Sarcoptes scabeii. Female mites that have bred successfully burrow into the skin (causing tracks), and lay eggs. The generalized rash occurs as an allergic and irritant reaction to the mites themselves. The condition is typically spread via skin to skin contact, though it may be acquired from infected materials such as bedding, and may affect anyone. This is a human mite so it cannot be caught from animals. Scabies tends to be species specific when it comes to their host. We just don't taste good to the dog scabies mite. The dog scabies mite causes sarcoptic mange and is not usually spread to humans; however, dog mites may occasionally bite us but these mites won't live on our skin.

Differential Diagnosis (Other conditions with similar appearance)Acropustulosis of infancy
Insect Bites
Asteatotic Eczema
Kyrle disease
Atopic Dermatitis
Lice
Bedbug Bites

Diagnosis
Key Points
Initial diagnosis based on clinical and microscopic examination
Dermoscopy may be performed to confirm diagnosis and rule out other conditions

Scabies is initially diagnosed based on a clinical and microscopic examination of the affected area. Dermoscopy may be performed to confirm the diagnosis and to rule out similar appearing conditions.

Treatment
Eliminate infestation
Treatment typically consists of administration of chemical insecticides.
Symptoms may persist for weeks after treatment in most cases. The mites are dead but the rash may take a few weeks to resolve.

The primary goal in treating scabies is to eliminate the infestation. This is typically accomplished with the administration of oral ivermectin, topical application of permethrin, or aqueous malathion lotions. These treatments typically eliminate the infestation within 3 days, though a follow up treatment is highly recommended. Most medications kill the living mites but do not kill the eggs; therefore, a repeat treatment is necessary in 7 to 14 days. Scabicides are typically applied on all skin areas from the chin down. Care should be taken to reduce risk of re-infestation by laundering all bedding and vacuuming carpets and furniture. Vacuum bags should be disposed of after the cleaning is complete. The condition typically takes 2-6 weeks to completely resolve after treatment.