Dermatologic Manifestations of Scabies Workup

  • Author: Kelly M Cordoro, MD; Chief Editor: Dirk M Elston, MD   more...
 
Updated: Dec 9, 2009
 

Laboratory Studies

The diagnosis is confirmed by light microscopic identification of mites, larvae, ova, or scybala (fecal pellets) in skin scrapings, as in the image below.

Scabies preparation demonstrating a mite and ova. Scabies preparation demonstrating a mite and ova. Courtesy of William D. James, MD.

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 of scabies.

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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.[7]

Immunosuppression, either medication or disease related, may be associated with crusted scabies.

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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.[8]

  • 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 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.

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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, as in the image below.

In crusted scabies, sections show multiple mites (In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum. The epidermis is spongiotic (hematoxylin and eosin; original magnification, 100X).

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, as in the image below. Biopsy of older lesions is nondiagnostic, demonstrating only excoriation and scale crusts.

In routine scabies, a single mite is seen. EosinopIn routine scabies, a single mite is seen. Eosinophilic spongiosis may be present (hematoxylin and eosin; original magnification, 400X).

Crusted scabies demonstrates massive hyperkeratosis of the stratum corneum with innumerable mites in all stages of development, as demonstrated in the image below. 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.

In crusted scabies, sections show multiple mites (In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum. The epidermis is spongiotic (hematoxylin and eosin; original magnification, 100X).

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.

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Contributor Information and Disclosures
Author

Kelly M Cordoro, MD  Assistant Professor of Pediatric and Adult Dermatology, Department of Dermatology, University of California, San Francisco 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.

Catharine Lisa Kauffman, MD, FACP  Georgetown Dermatology and Georgetown Dermpath

Catharine 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.

Specialty Editor Board

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.

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.

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.

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 Investigator; Genentech Grant/research funds investigator; Centocor Consulting fee Consulting; Abbott Grant/research funds investigator; Abbott Consulting fee Consulting; Novartis investigator; Pfizer Grant/research funds investigator; Celgene Consulting fee DMC Chair; NIAMS and NHLBI Grant/research funds investigator

Chief Editor

Dirk M Elston, MD  Director, Department of Dermatology, Geisinger Medical Center

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

References

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Scabies mite scraped from a burrow (original magnification, 400X).
A typical linear burrow on the flexor forearm. Courtesy of Kenneth E. Greer, MD.
A subtle linear burrow accompanied by erythematous papules on the sole of the foot in a child with scabies. Courtesy of Kenneth E. Greer, MD.
Erythematous papules and papulovesicles on the flexor wrist. Courtesy of Kenneth E. Greer, MD.
Scabies on the penile shaft and glans. Courtesy of William D. James, MD.
Scabietic papules on the penile shaft and scrotum. Courtesy of Kenneth E. Greer, MD.
Widespread eruption on the back of an infant with scabies. Courtesy of Kenneth E. Greer, MD.
Nodular scabies in an infant. Courtesy of Kenneth E. Greer, MD.
Nodular scabies. Courtesy of Kenneth E. Greer, MD.
Crusted scabies. Courtesy of William D. James, MD.
Crusted scabies. Courtesy of Kenneth E. Greer, MD.
Scabies preparation demonstrating a mite and ova. Courtesy of William D. James, MD.
Scabies. Erythematous vesicles and papules are present on torso extremities, some with adjacent linear excoriations.
In routine scabies, a single mite is seen. Eosinophilic spongiosis may be present (hematoxylin and eosin; original magnification, 400X).
Scabies mite in the stratum corneum. Courtesy of William D. James, MD.
In crusted scabies, sections show multiple mites (arrows) within the hyperkeratotic stratum corneum. The epidermis is spongiotic (hematoxylin and eosin; original magnification, 100X).
Scabies. Courtesy of William D. James, MD.
Scabies in the interdigital web spaces. Courtesy of William D. James, MD.
Papulovesicles and nodules on the palm in a patient with scabies. Courtesy of Kenneth E. Greer, MD.
 
 
 
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