Scabies (pediatric) - Anogenital in
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Synopsis
Scabies is a parasitic infestation of the epidermis. It is caused by the obligate human parasite Sarcoptes scabiei var hominis and is transmitted via direct skin-to-skin contact (usually 10-20 minutes' contact) and rarely by fomites such as bedding and clothing. Scabies affects all ethnic groups and socioeconomic levels. Scabies is most common in young children, and the highest prevalence is seen in children younger than 2 years. It is extremely contagious, spreading between individuals who share close contact or living spaces. Frequent outbreaks occur in schools, group homes, and orphanages where direct contact with infested individuals is common. The most common predisposing factors are overcrowding, poverty, poor nutrition, and being undomiciled. Other predisposing conditions include immunocompromised status, HIV infection, and severe intellectual or physical disability. The highest prevalence of infestation is seen in tropical regions such as Central America, the Northern Territory of Australia, and the Pacific Islands.
Infestation begins with the female mite, which burrows within the stratum corneum of the host and lays its eggs. The eggs develop into larvae, nymphs, and adults. The average number of adult female mites in an infested individual is 10-15, but this number can be much larger in those who are immunocompromised. If separated from human hosts, the mite can survive at most a few days. Symptoms and signs typically develop approximately 3 weeks after the primary infestation.
Clinically, scabies infestation manifests in 3 ways: classic, nodular, or crusted (previously called Norwegian scabies).
- Classic scabies in children presents with pruritic papules affecting flexural areas, including the axillary folds, wrists, and dorsal ankles; the interdigital web spaces of the hands and feet; anogenital area; and truncal areas, especially around the nipples and periumbilical areas (the circle of Hebra). It is accompanied by itch, which is classically worse at night, especially just after getting into bed.
- Nodular scabies, a clinical variant of classic scabies, is less common in children than in adults. It is considered a hypersensitivity reaction to the mite and manifests with erythematous nodules.
- The crusted variant of scabies is most common in individuals who are immunocompromised. It presents with widespread scaly, crusted, or hyperkeratotic papules and plaques. Scales may have a powdery texture. Pruritus may be severe but is usually minimal or absent. Nail dystrophy can be present. It is extremely contagious due to the high mite burden; there may be up to a million mites on a single individual.
Codes
ICD10CM:B86 – Scabies
SNOMEDCT:
128869009 – Infestation by Sarcoptes scabiei var hominis
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Differential Diagnosis & Pitfalls
- Papular urticaria – A hypersensitivity reaction to a variety of bites, such as mosquitoes, fleas, bedbugs, and mites. There may be a seasonal occurrence. Recurrent episodes of excoriated papular and urticarial lesions on the exposed parts of the extremities (extensor aspect) are the cardinal features. Absence of burrows and family history of itching differentiate this from scabies.
- Atopic dermatitis – Eczematous lesions with oozing on the face and flexural areas (cubital and popliteal fossa). Lichenification is seen in chronic dermatitis. Burrows are absent, and lesions are not seen in the web spaces.
- Impetigo – Erythematous vesiculopustular lesions that rupture, forming the pathognomonic honey-colored crust. Lesions may involve the face, neck, and extremities. Scabies may sometimes be impetiginized, so a good history may distinguish primary versus secondary impetigo.
- Erythema toxicum neonatorum – Appears in the first 2-4 days of life and spontaneously resolves within hours to days. Tzanck smear from a pustule reveals numerous eosinophils.
- Transient neonatal pustular melanosis – Presents at birth with fragile pustules and hyperpigmented macules. Pustules spontaneously resolve within 2 weeks.
- Neonatal herpes – Discrete or grouped vesicles on an erythematous base, possibly with systemic symptoms. Tzanck smear from the vesicle reveals multinucleated giant cells.
- Congenital cutaneous candidiasis – Presents at birth, may affect the nails, may be associated with placental lesions and inflammation. Potassium hydroxide (KOH) preparation of vesicular contents reveals yeast and pseudohyphae.
- Cutaneous candidiasis – Affects the intertriginous areas, especially the groin or neck, in the form of confluent erythematous patches with multiple, small satellite pustules. KOH test from a pustular lesion reveals budding spores and pseudohyphae.
- Infantile acropustulosis – Thought by many authors to be precipitated by scabies.
- Eosinophilic folliculitis of infancy – Extremely pruritic; scalp involvement may differentiate from scabies.
- Folliculitis
- Nummular dermatitis
- Langerhans cell histiocytosis
- Insect bites
- Tinea corporis
- Dermatitis herpetiformis
- Eczema herpeticum
- Pityriasis rosea
- Viral exanthems
- Prurigo nodularis
- Leukemia or lymphoma cutis
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References
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Last Reviewed:02/15/2023
Last Updated:04/06/2023
Last Updated:04/06/2023
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Scabies (pediatric) - Anogenital in
See also in: Overview