Skin nontumor

Infestations

Scabies (mite)



Minor changes: 8 September 2021

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PubMed Search: Scabies[TI] mite[TI]

See Also: Penis & scrotum chapter

Bethany R. Rohr, M.D.
Eric W. Hossler, M.D.
Page views in 2020: 4,709
Page views in 2021 to date: 4,829
Cite this page: Rohr BR, Hossler EW. Scabies (mite). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumorscabies.html. Accessed October 21st, 2021.
Definition / general
  • Scabies are 8 legged mites that infest the stratum corneum
  • Cause intense pruritus accompanied by a variety of cutaneous findings; infestation may lead to secondary impetiginization and psychological sequelae
Essential features
  • Obligate ectoparasite
  • Burrows into the stratum corneum of acral and intertriginous sites
  • Diagnosis is through visualization of burrows on clinical exam or through identification of mites, eggs or scybala on microscopy
Terminology
  • Itch mite, Sarcoptes scabiei var. hominis
ICD coding
  • ICD-10: B86 - scabies
Epidemiology
Sites
  • Finger and toe webs
  • Volar surfaces of wrists
  • Intertriginous areas
  • Areas under occlusion (i.e. waistbands)
  • Areola (females), genitalia (males)
  • Spares head (high sebaceous areas) in adults, immune competent (Dermatol Ther 2020;33:e13746)
  • May affect head in infants, immunocompromised
Pathophysiology
  • Skin to skin transmission or fomites
  • Classic scabies: mite load 5 - 15 mites (J Am Acad Dermatol 2020;82:533)
    • Th1 / Th2 immune response
  • Crusted scabies: 100s - 1,000s of mites
    • Th2 response
  • Mites burrow into stratum corneum
Etiology
Diagrams / tables

Images hosted on other servers:
Life cycle

Life cycle

Diagnostic criteria for scabies

Diagnostic criteria for scabies

Clinical features
  • Initial symptom onset 4 - 6 weeks post initial infection (J Am Acad Dermatol 2020;82:533)
  • Subsequent infection symptom onset within days (J Am Acad Dermatol 2020;82:533)
  • Classic presentation:
    • Extreme pruritus, nighttime worsening
    • Burrows
      • Small white serpiginous scaly linear papules on finger and toe webs
    • Erythematous scaly papules on intertriginous, areolar and genital skin and areas under occlusion
      • Excoriations common
  • Genital / scrotal erythematous nodules (IDCases 2020;22:e00947)
  • With or without pruritus in infants, immunosuppressed and patients on topical steroids (J Am Acad Dermatol 2020;82:533)
  • With or without secondary impetiginization or autoeczematization
  • Crusted scabies
    • Yellow to white hyperkeratotic plaques
  • With or without postscabetic pruritus for 4+ weeks posttreatment
    • Use topical corticosteroids, education
Diagnosis
  • Mineral oil scraping (low sensitivity)
  • Clinical exam (burrows on finger and toe webs, genital nodules)
  • Dermoscopy (delta wing jet sign) (Tidsskr Nor Laegeforen 2020;140:1)
  • Other noninvasive techniques: videodermoscopy, confocal microscopy, optical coherence tomography (J Am Acad Dermatol 2020;82:533)
  • Skin biopsy (shave or punch)
Laboratory
Prognostic factors
Case reports
Treatment
  • Permethrin 5% cream
    • First line
    • Close contacts treated simultaneously
    • FDA approved for > 2 months age
  • Oral ivermectin
  • Less commonly used (J Am Acad Dermatol 2020;82:533):
    • Benzyl benoate 10 - 25%
    • Precipitated sulfur 2 - 10%
    • Crotamiton 10%
    • Malathion 0.5%
    • Lindane 1%
Clinical images

Images hosted on other servers:
Penile nodules

Penile nodules

Web spaces

Web spaces

Genital papulonodules Genital papulonodules

Genital papulonodules

Areolar papules

Areolar papules

Burrow

Burrow

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Eric W. Hossler, M.D. and Bethany R. Rohr, M.D.
Crusted scabies

Crusted scabies

Numerous mites

Numerous mites

Crusted scabies Crusted scabies

Crusted scabies

Crusted scabies Crusted scabies

Crusted scabies


Crusted scabies

Crusted scabies

Scraping of adult mite

Scraping of adult mite

Scraping of an egg

Scraping of an egg

Ova and scybala

Ova and scybala

Mite anatomy

Mite anatomy

Intracorneal mite

Intracorneal mite


Adult mite

Adult mite

Ova on skin scraping

Ova on skin scraping

Setae

Setae

Mite on skin scraping

Mite on skin scraping

Rudimentary front legs

Rudimentary front legs

Virtual slides

Images hosted on other servers:
Scabies

Scabies

Scabies mineral scraping

Scabies mineral oil scraping

Crusted scabies

Crusted scabies

Crusted scabies clinical

Crusted scabies clinical

Positive stains
Videos

Probe of scabies burrow under dermoscopy

 

Ask a dermatologist: how do I get rid of scabies?

Sarcoptes scabiei var. hominis

Sample pathology report
  • Skin, anatomic location, (punch or shave) biopsy:
    • Scabies
Differential diagnosis
Board review style question #1
A biopsy from a patient with crusted scabies is likely to reveal which findings compared with typical scabies?

  1. Few mites
  2. Few ova
  3. Many ova but few mites
  4. Mites present in the upper dermis
  5. Numerous mites, ova and scybala
Board review style answer #1
E. Numerous mites, ova and scybala. Crusted scabies occurs in immunosuppressed patients and characteristically contains hyperkeratosis with numerous mites, ova and scybala. Scabies mites reside in the epidermis only.

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Reference: Scabies (mite)
Board review style question #2

Scabies invade into which level of the skin?

  1. Papillary dermis
  2. Reticular dermis
  3. Stratum corneum
  4. Stratum granulosum
  5. Stratum spinosum
Board review style answer #2
C. Stratum corneum

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Reference: Scabies (mite)
Board review style question #3
Scabies mites avoid which anatomic region, except in infants and immunosuppressed patients?

  1. Acral sites
  2. Genitals
  3. Head (face, scalp)
  4. Intertriginous areas
  5. Volar wrists
Board review style answer #3
C. Head (face, scalp); scabies typically avoid the face / scalp (highly sebaceous areas) in immunocompetent adults. The other listed sites are typical areas of involvement.

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Reference: Scabies (mite)
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