Scabies | Atlas Dermato

General information

Cutaneous infestation caused by the mite Sarcoptes scabiei var. hominis.
Highly contagious, primarily transmitted through prolonged, close skin-to-skin contact.
Transmission through contaminated clothing, bedding, or other fomites can occur but is particularly important in crusted scabies.
Incubation after a first infestation: usually 4–6 weeks before pruritus develops.
With reinfection: symptoms typically develop much more rapidly, usually within 1–4 days.
Outbreaks are facilitated by crowding and close contact, particularly in households, long-term care facilities, daycare centers, shelters, and correctional facilities.
Crusted scabies is a highly contagious form with an extremely high mite burden, particularly affecting selected elderly, neurologically impaired, or immunocompromised patients.

Intense pruritus +++, characteristically worse at night.
Pruritus may be generalized despite relatively localized skin lesions.
Multiple household members or close contacts with itching is an important diagnostic clue.
History of close contact with an affected individual or exposure during an institutional outbreak may be present.
Transmission may occur through prolonged sexual contact.
Pruritus primarily results from a hypersensitivity reaction to the mites, eggs, and their products.

Intensely pruritic erythematous papules, frequently excoriated.
Vesicles, pustules, and secondary crusting may occur.
Scabies burrow = characteristic lesion: a thin, serpiginous, grayish or brownish line representing the intraepidermal tunnel created by the mite.
Persistent scabetic nodules may occur, particularly in the genital, axillary, and inguinal regions.
Excoriations and crusting secondary to scratching are common.
Secondary bacterial infection/impetiginization may occur.
Crusted scabies: thick hyperkeratotic, scaly, and crusted plaques containing extremely large numbers of mites; pruritus may be mild or absent.

Interdigital web spaces +++.
Flexor surfaces of the wrists +++.
Elbows and axillae.
Waistline and periumbilical region.
Buttocks.
Genital region, particularly in men.
Nipples/areolae may be involved.
In immunocompetent adults, the face and scalp are generally spared.
In infants and young children, the face, scalp, palms, and soles may be involved.
In elderly or immunocompromised patients, involvement may be more diffuse or atypical.

Visualization of the scabies burrow.
Characteristic “delta-wing jet with contrail” sign: a brown triangular structure at the end of the burrow corresponding to the anterior portion of the mite.
The burrow represents the “contrail” extending behind the mite.
Dermoscopy can help locate the mite and guide skin scraping when confirmation is required.

Often a clinical diagnosis based on nocturnal pruritus, typical distribution, affected contacts, and/or characteristic burrows.
Dermoscopy can directly identify the mite within a burrow.
Skin scraping with microscopy demonstrating mites, eggs, or fecal pellets confirms the diagnosis.
A negative scraping does not exclude scabies, because mite burden is relatively low in classic scabies.
Assess household members and close contacts for additional cases.

Atopic dermatitis.
Contact dermatitis.
Prurigo.
Arthropod/insect bites.
Papular urticaria.
Pediculosis.
Folliculitis.
Dermatitis herpetiformis.
Other causes of generalized pruritus, particularly when specific lesions are absent.

Permethrin 5% cream = first-line topical therapy in many guidelines.
Apply thoroughly to the entire body from the neck down, including interdigital spaces, between the toes, under the nails, umbilicus, genital region, and buttocks.
Leave on for approximately 8–14 hours, then wash off.
Repeat approximately 7 days later to eradicate newly hatched mites.
In infants, young children, older adults, or when the scalp is involved, treatment should also include the scalp and appropriate facial areas while avoiding the eyes and mouth.
Alternative or appropriate treatment in selected patients: oral ivermectin 200 µg/kg, generally repeated 7–14 days later.
Treat household members and close contacts simultaneously, even when asymptomatic when indicated by exposure and local recommendations.
Wash recently used clothing, towels, and bedding using a hot cycle and hot dryer; items that cannot be washed can be sealed away for several days.
Pruritus may persist for several weeks after successful treatment and does not necessarily indicate treatment failure.
Crusted scabies generally requires combined oral ivermectin + topical permethrin using repeated doses/applications, along with contact precautions and specialist-directed management.