A 32-year-old man presents with lesions scattered between his fingers. The lesions appear excoriated, crusted, erythematous, scaling, and tender. On examination, the patient reveals that he had this itchy, bumpy rash for a month and that he had recently returned to the United States from a trip to India, where he was teaching children in underdeveloped regions of the country.
The patient complains mainly of itching that has not been relieved by over-the-counter topical medications such as hydrocortisone cream.
What is the diagnosis?
- seborrheic dermatitis
- pityriasis rosea
- insect bites
The correct answer is c) scabies.
Approximately 300 million people worldwide are infected with scabies each year. 1,2 Caused by the parasite Sarcoptes scabiei, scabies largely targets people in underdeveloped countries or those who live in overcrowded conditions with poor hygiene practices. 1
Lesions occur at the mite invasion site, developing from hypersensitivity to mite infection, chronic scratching, and secondary infections. These maculopapular lesions are found near the burrow sites—commonly areas with few hair follicles and where the skin layer is soft and thin, such as the axilla, elbows, finger webs, genitalia, buttocks, knees, waist, and toes. 1-8
Lesions that develop as a result of hypersensitivity to mites are edematous papules; lesions of chronic scratching due to pruritus and secondary infections appear excoriated, crusted, erythematous, scaling, and tender. 2,5-7
Scabies is transmitted through nonsexual and sexual contact. Nonsexual transmission can stem from handshakes, infected bedding, clothing, and toilet seats. The communicability period lasts until the infected person has been treated and all infected body surfaces and surrounding environment have been disinfested.
Making a Diagnosis
Scabies is diagnosed based on the patient’s clinical presentation, including history and physical findings. Ask patients the following:
- When did you first notice skin lesions, where are they located, and how long have you had them?
- Has the rash spread to any other areas of your body?
- Do you experience itching? If so, is it worse during the day or at night?
- Do you have any other symptoms?
- Do you know what may have caused the skin lesions?
- Do any of your family or friends have the same symptoms as you?
- Have you been treating your lesions and, if so, with what? Did you get relief?
Diagnosis can be microscopically confirmed when skin scrapings or extraction of burrows or papule material reveal fecal pellets, mites, or ova. 2,4,9 In case of secondary infection, group A streptococcus or Staphylococcus aureus is identified on hematologic culture. 5
To treat scabies, permethrin 5% cream is believed to be the safest of the scabicide preparations. It can be applied from the neck down to all areas of the body, and left in situ for 8 to 14 hours. 10,11 If live lice are still apparent, reapplication is necessary. 2,6,7
Lindane 1% lotion or cream, another topical treatment, is applied similar to permethrin. Lindane should not be used for patients with extensive dermatitis, infants or toddlers, or pregnant or breast-feeding women. 7,11
Last year, the Food and Drug Administration issued an advisory concerning the use of Lindane lotion and shampoo. A boxed warning emphasizes that it is a second-line treatment; updates information about its potential risks, especially in patients weighing less than 110 pounds; and reminds clinicians that reapplication of Lindane lotion or Lindane shampoo is not appropriate if itching continues after the single treatment.
Sulfur 10% in petroleum, crotamiton 10% cream, and ivermectin 0.8% cream are other effective, classic remedies for scabies. A single oral dose of ivermectin, 200 mcg/kg, is also used to treat scabies in HIV-infected individuals. Secondary and extensive infections unresponsive to therapy are treated with antibiotics. 6,11
Other Possibilities Discounted
Seborrheic dermatitis has maculopapular lesions that appear yellowish-red and greasy or white, dry, and scaly. People with this condition have a rash, pruritis, and excoriated erythematous skin in body folds, axillae, and groin. 7
Pityriasis rosea also resembles scabies and primarily affects the trunk; it is not contagious. These lesions are salmon pink or tawny-colored and oval-shaped. The large, oval-shaped herald and “Christmas tree”shape of the lesions make pityriasis rosea’s presentation somewhat unique. 7
Insect bites are characterized by erythematous-based papules and intense pruritis. Microscopically, insect bites present as urticaria in a zigzag pattern, especially on the legs and at the waist—similar to the patterns found in scabies. 7
1. Walker GJA, Johnston PW. Interventions for treating scabies. In the Cochrane Library, Issue 1, 2003. Oxford: Update Software. Available at http://www.update-software.com
. Accessed March 14, 2003.
2. Chosidow O. Seminar. Scabies and pediculosis. Lancet (North American Edition) 2000;355(9606):819-26.
3. Fitzpatrick TB, Johnson RA, Wolff K, et al. Color Atlas and Synopsis of Clinical Dermatology. 3rd ed. New York, NY: McGraw-Hill; 1997. p 842-9.
4. Rana-Mukkavilli G. Case & comment: medical mysteries to sharpen your diagnostic skills. What caused this young man’s pruritis? Patient Care Nurse Practitioner 2001;4(9):49.
5. Friday JH. Pruritis: scabies. In: Swartz JM, editor. Clinical Handbook of Pediatrics. 2nd ed. Baltimore, MD: Williams & Wilkins; 1999. p 549-56.
6. Kumar M. Scabies. In Emedicine
: Instant access to the minds of medicine. September 14, 2001. Available at http://www.emedicine.com/ped/topoc2047.htm
. Accessed March 24, 2003.
7. Uphold CR, Graham MV. Scabies. Clinical Guidelines in Family Practice. 3rd ed. Gainesville, FL: Barmarrae Books; 1998. p 279-80.
8. Zitelli B, Davis H. Atlas of Pediatric Physical Diagnosis. 3rd ed. St. Louis, MO: Mosby; 1997. p 239-40, 549-50.
9. Ralph D. Is it or isn’t it? Nurs Stand 2001;16(3):25.
10. Hansen RC. Scabies: treatable following a diagnosis. Healthline 1999;16(12):1-3.
11. Wilson BA, Shannon MT, Stang CL. Nurse’s Drug Guide 2002. Upper Saddle River, NJ: Prentice Hall; 2002.