eMedicine Specialties > Dermatology > Parasitic Infections

Scabies: Differential Diagnoses & Workup

Author: Kelly M Cordoro, MD, Fellow and Clinical Instructor, Department of Pediatric Dermatology, University of California at San Francisco; Assistant Professor (On Educational Leave), Assistant Program Director for Resident Medical Education, Department of Dermatology, University of Virginia School of Medicine
Coauthor(s): Barbara B Wilson, MD, Edward P Cawley Associate Professor, Department of Dermatology, University of Virginia School of Medicine; C Lisa Kauffman, MD, FACP, Professor, Chief, Division of Dermatology, Departments of Medicine and Pathology, Georgetown University Medical Center
Contributor Information and Disclosures

Updated: Nov 12, 2008

Differential Diagnoses

Acropustulosis of Infancy
Insect Bites
Asteatotic Eczema
Kyrle Disease
Atopic Dermatitis
Lice
Bedbug Bites
Lichen Planus
Chickenpox
Neurotic Excoriations
Contact Dermatitis, Allergic
Papular Urticaria
Contact Dermatitis, Irritant
Parapsoriasis
Dermatitis Artefacta
Prurigo Nodularis
Dermatitis Herpetiformis
Psoriasis, Guttate
Dermatologic Manifestations of Renal Disease
Psoriasis, Pustular
Dyshidrotic Eczema
Seabather's Eruption
Eosinophilic Pustular Folliculitis
Syphilis
Erythroderma (Generalized Exfoliative Dermatitis)
Urticaria, Cholinergic
Folliculitis
Vesicular Palmoplantar Eczema
Gianotti-Crosti Syndrome (Papular Acrodermatitis of Childhood)
Id Reaction (Autoeczematization)

Other Problems to Be Considered

Pruritus with or without rash
Adverse cutaneous drug reaction
Fiberglass dermatitis
Dermatographism
Dermatitis herpetiformis
Animal scabies
Delusions of parasitosis
Metabolic pruritus
Paraneoplastic Pruritus

Nodular scabies
Urticaria pigmentosa (in young child)
Lymphoma

Crusted scabies
Psoriasis
Seborrheic dermatitis
Langerhans cell histiocytosis

Workup

Laboratory Studies

  • The diagnosis is confirmed by light microscopic identification of mites, larvae, ova, or scybala (fecal pellets) in skin scrapings (see Media File 12).
  • In rare cases, mites are identified in biopsy specimens obtained to rule out other dermatoses. Characteristic histopathology in the absence of actual mites also may suggest the diagnosis.

Other Tests

  • Elevated immunoglobulin E titers and eosinophilia may be demonstrated in some patients with scabies.
  • Clinically inapparent infection can be detected by amplification of Sarcoptes DNA in epidermal scale by polymerase chain reaction.2
  • Immunosuppression, either medication or disease related, may be associated with crusted scabies.

Procedures

  • Skin scraping: Place a drop of mineral oil on a glass slide, touch a No. 15 blade or a 7-mm curette to the oil, and scrape infested skin sites, preferably primary lesions such as vesicles, juicy papules, and burrows (see 3 ).
    • The skin scrapings are placed on a glass slide, covered with a coverslip, and examined under a light microscope at 40X magnification.
    • Multiple scrapings may be required to identify mites or their products. Persistence is key to accurate diagnosis.
  • Burrow ink test: The tip of a fountain pen is rubbed along the site of a possible burrow. The ink penetrates the burrow, distinguishing it from the surrounding tissue. The excess ink is wiped off with an alcohol pad. This technique is particularly useful in children and individuals with very few burrows.
  • Alternative to burrow ink test: Topical tetracycline solution is an alternative to the burrow ink test. After application and removal of the excess tetracycline solution with alcohol, the burrow is examined under a Wood's light. The remaining tetracycline within the burrows fluoresces a greenish color. This method is preferred because tetracycline is a colorless solution and large areas of skin can be examined.
  • Crusted scabies: Add 10% potassium hydroxide (KOH) to the skin scraping. This dissolves excess keratin and permits adequate microscopic examination.

Histologic Findings

The histologic features of scabies are distinctive enough to suggest the diagnosis, although they are common to a variety of arthropod reactions. If a burrow is excised, mites, larvae, ova, and feces may be identified within the stratum corneum. A superficial and deep dermal infiltrate composed of lymphocytes, histiocytes, mast cells, and eosinophils is characteristic. Spongiosis and vesicle formation with exocytosis of eosinophils and occasional neutrophils is present. Biopsy of older lesions is nondiagnostic, demonstrating only excoriation and scale crusts.

Crusted scabies demonstrates massive hyperkeratosis of the stratum corneum with innumerable mites in all stages of development. Psoriasiform hyperplasia of the underlying epidermis with spongiotic foci and occasional epidermal microabscesses is present. The dermis shows a superficial and deep chronic inflammatory infiltrate with admixed interstitial eosinophils.

Nodular scabies reveals a dense, mixed, superficial, and deep dermal inflammatory cell infiltrate. Lymphoid follicles may be present, and the infiltrate occasionally extends into the subcutaneous fat. Mite parts may be seen on serial sectioning in up to 20% of cases.

More on Scabies

Overview: Scabies
Differential Diagnoses & Workup: Scabies
Treatment & Medication: Scabies
Follow-up: Scabies
Multimedia: Scabies
References
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References

  1. Haubrich WS. Medical Meanings: A Glossary of Word Origins. Philadelphia, Pa: American College of Physicians; 1997:200.

  2. Bezold G, Lange M, Schiener R, Palmedo G, Sander CA, Kerscher M, et al. Hidden scabies: diagnosis by polymerase chain reaction. Br J Dermatol. Mar 2001;144(3):614-8. [Medline].

  3. Johnston G, Sladden M. Scabies: diagnosis and treatment. BMJ. Sep 17 2005;331(7517):619-22. [Medline].

  4. Aubin F, Humbert P. Ivermectin for crusted (Norwegian) scabies. N Engl J Med. Mar 2 1995;332(9):612. [Medline].

  5. Huffam SE, Currie BJ. Ivermectin for Sarcoptes scabiei hyperinfestation. Int J Infect Dis. Jan-Mar 1998;2(3):152-4. [Medline].

  6. Elgart GW, Meinking TL. Ivermectin. Dermatol Clin. Apr 2003;21(2):277-82. [Medline].

  7. Brodell RT, Helms SE. Bedside testing: the diagnostic cornerstone of dermatology. Compr Ther. Mar 1997;23(3):211-7. [Medline].

  8. Burgess I. Sarcoptes scabiei and scabies. Adv Parasitol. 1994;33:235-92. [Medline].

  9. Burkhart CG, Burkhart CN, Burkhart KM. An epidemiologic and therapeutic reassessment of scabies. Cutis. Apr 2000;65(4):233-40. [Medline].

  10. Fitzpatrick TB, Austen KF, Wolff K, et al, eds. Dertmatology in General Medicine. 4th ed. New York, NY: McGraw-Hill; 1993:1812-3.

  11. Elgart ML. Scabies. Dermatol Clin. Apr 1990;8(2):253-63. [Medline].

  12. Fitzpatrick TB, Johnson RA, Wolff K. Inset Bites and Infestations. In: Fitzpatrick TJ, Johnson RA, Wolff K, Polano MK, Suurmond R, eds. Color Atlas and Synopsis of Clinical Dermatology. 3rd ed. New York, NY: McGraw-Hill; 1997:836-61.

  13. Guldbakke KK, Khachemoune A. Crusted scabies: a clinical review. J Drugs Dermatol. Mar 2006;5(3):221-7. [Medline].

  14. Karthikeyan K. Treatment of scabies: newer perspectives. Postgrad Med J. Jan 2005;81(951):7-11. [Medline].

  15. McCarthy JS, Kemp DJ, Walton SF, Currie BJ. Scabies: more than just an irritation. Postgrad Med J. Jul 2004;80(945):382-7. [Medline].

  16. Molinaro MJ, Schwartz RA, Janniger CK. Scabies. Cutis. Dec 1995;56(6):317-21. [Medline].

  17. Orkin M, Maibach HI. Scabies treatment: current considerations. Curr Probl Dermatol. 1996;24:151-6. [Medline].

  18. Paller AS. Scabies in infants and small children. Semin Dermatol. Mar 1993;12(1):3-8. [Medline].

  19. Schleicher SM, Stewart P. Scabies: the mite that roars. Emerg Med. 1997;6:54-8.

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Further Reading

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Keywords

human scabies, seven-year itch, 7-year itch, itch mites, pruritic eruption, Sarcoptes scabiei, S scabiei, Sarcoptes scabiei var hominis, S scabiei var hominis, skin infestation, skin mite, pruritic skin disease, pruritus, crusted scabies, Norwegian scabies, mite infestation

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Contributor Information and Disclosures

Author

Kelly M Cordoro, MD, Fellow and Clinical Instructor, Department of Pediatric Dermatology, University of California at San Francisco; Assistant Professor (On Educational Leave), Assistant Program Director for Resident Medical Education, Department of Dermatology, University of Virginia School of Medicine
Kelly M Cordoro, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, Association of Professors of Dermatology, Dermatology Foundation, Medical Society of Virginia, National Psoriasis Foundation, Society for Pediatric Dermatology, and Women's Dermatologic Society
Disclosure: Nothing to disclose.

Coauthor(s)

Barbara B Wilson, MD, Edward P Cawley Associate Professor, Department of Dermatology, University of Virginia School of Medicine
Barbara B Wilson, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, Medical Society of Virginia, and Sigma Xi
Disclosure: Nothing to disclose.

C Lisa Kauffman, MD, FACP, Professor, Chief, Division of Dermatology, Departments of Medicine and Pathology, Georgetown University Medical Center
C Lisa Kauffman, MD, FACP is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Royal Society of Medicine, Society for Investigative Dermatology, and Women's Dermatologic Society
Disclosure: Nothing to disclose.

Medical Editor

Daniel J Hogan, MD, Clinical Professor of Internal Medicine (Dermatology), NOVA Southeastern University; Investigator, Hill Top Research, Florida Research Center
Daniel J Hogan, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Contact Dermatitis Society, and Canadian Dermatology Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Paul Krusinski, MD, Director of Dermatology, Professor, Department of Internal Medicine, Fletcher Allen Health Care, University of Vermont
Paul Krusinski, MD is a member of the following medical societies: American Academy of Dermatology, American College of Physicians, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

CME Editor

Joel M Gelfand, MD, MSCE, Medical Director, Clinical Studies Unit, Assistant Professor, Department of Dermatology, Associate Scholar, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania
Joel M Gelfand, MD, MSCE is a member of the following medical societies: Society for Investigative Dermatology
Disclosure: AMGEN Consulting fee Consulting; AMGEN Grant/research funds None; Genentech Consulting fee Consulting; Centocor Consulting fee Consulting; Centocor Grant/research funds None; Covance Consulting fee Consulting; Shire  Consulting

Chief Editor

William D James, MD, Paul R Gross Professor of Dermatology, University of Pennsylvania School of Medicine; Vice-Chair, Program Director, Department of Dermatology, University of Pennsylvania Health System
William D James, MD is a member of the following medical societies: American Academy of Dermatology and Society for Investigative Dermatology
Disclosure: elsevier Royalty Other; american college of physicians Honoraria Other

 
 
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