Three-year-old displaying rash on feet.
A 3-year-old girl presents to the clinic with a history of “itchy rash on hands and feet” that started 2 days earlier. On examination, the patient displays multiple small, erythematous papules on the palms, sides, and webs of her hands and fingers, and on the palms of her feet. The mother notes that the pruritus became worst the night before, and caused her child not to sleep well. The mother also states that she is also feeling itchy, but thought it was “all in her head.” The patient attends daycare while the mother is at work.
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Scabies is a highly contagious parasitic infection that has plagued humans throughout history, and is described both in the Bible and in Aristotle’s writing.1 The term “scabies” is credited to Roman physician Celcius,1 but the causal relationship between the scabies mite and the skin manifestations was not described until 1687 by Giovan Cosimo Bonomo and Diacinto Cestoni.2
The incidence of scabies is higher in developing counties, especially among those in the lower socioeconomic classes, but scabies can affect anyone regardless of sex, age, or ethnicity.2-7 It is estimated to affect 300 million people a year worldwide.3-5 Some areas of the world experience seasonal increases in incidence during the winter, possibly because mites survive away from their host better in cooler environments.2,3
Sarcoptes scabiei is the mite responsible for this condition.2-8 Scabies transmission occurs predominately via direct contact with an infected individual.3,6-8 Theoretically, scabies can also occur via fomites, but studies have shown that clinically, this mode of transmission is rare.2,3 Because scabies can also infect animals, such as domestic pets, animal-to-human transmission is rare but possible.5 Genital scabies infection occurs via sexual transmission.3
Once in contact with a new host, the pregnant female parasite burrows into the upper stratum of the epidermis and lays eggs.7,8 The larvae will mature and repeat the cycle in about 2 weeks.7 In classic cases of scabies, an individual is host to 10 to 12 mites.2,7 In crusted scabies, a severe infestation that affects immunocompromised individuals, counts can reach into the millions.2 The risk of contracting scabies is higher in environments where people are in close contact with infected individuals. This can occur in healthcare settings such as hospitals and nursing homes, in crowded housing situations, and in prisons.2,3,5,6
Classical scabies presents as pruritic, erythematous papules that symptomatically worsen at night.2,3,7,8 Because of its highly contagious nature, patients with scabies may present with several family members also experiencing similar symptoms.7 The papules may progress to vesicles and bullae.2 These symptoms occur as a hypersensitivity response to the infestation.3
During the primary infection, symptoms are delayed in onset as the adaptive immune response is generated. If an individual is reinfected, symptoms occur within a day.2 The most common locations are the finger webs, wrists, elbows, axillae, buttocks, genitalia, and breasts.3,7 In adults, the head is generally spared, but in infants, the face and scalp are commonly affected.3,7 Because neonates cannot scratch, they present as poorly feeding and irritable, with pinkish-brown nodules.7 The most specific clinical sign for scabies are burrows, which appear as short, wavy lines.2,3,7
Because this is a pruritic condition, excoriations are commonly seen and can lead to eczematization, crusting, and impetiginization.2,3 Superinfection with Streptococcus can lead to acute glomerulonephritis.2,6 Crusted scabies is a hyperkeratotic skin disease that presents with exfoliating scales.2 Predisposing conditions associated with this hyperinfestation are immunocompromising infections (HIV, human T-cell leukemia virus), neurological conditions, and institutionalization among elderly individuals.2,5,7
The differential diagnosis includes many of the other pruritic dermatoses. In developed countries, eczema, tinea, and atopic dermatitis are more common than scabies, whereas in developing countries, pyoderma is more likely. Crusted scabies appears to be very similar to psoriasis. Scabies can also mimic a variety of systemic diseases such as lupus erythematosus, bullous pemphigoid, Langerhans cell histiocytosis, urticaria pigmentosa, and seborrheic dermatitis.2
When diagnosing skin rashes with pruritus, it is important to have scabies on the differential diagnosis list and to perform a thorough physical examination, especially on patients coming to the hospital from a long-term care facility or from resource-poor settings. A recent study performed by Hong et al found that 65% of patients admitted to the hospital through the emergency department with scabies were not diagnosed on admission.4
Diagnosis can be made clinically, but historically, superficial skin scrapings have been examined in an attempt to identify mites, eggs, or remnants.3 This method of diagnosis is controversial because of its low sensitivity; thus, less-invasive methods are being studied.2 Epiluminescence microscopy and dermoscopy has been shown to be valuable diagnostic tools.6,8 The adhesive tape test is an alternative to skin scraping in resource-poor settings and when attempting to diagnose noncooperative children.8 Biopsies are rarely performed, but histologic examination typically reveals a nonspecific, delayed hypersensitivity reaction.3 If a mite is visualized, it is surrounded by eosinophils, lymphocytes, and histiocytes.2
In the United States, permethrin cream (5%) is used as first-line therapy.2,7 Benzyl benzoate cream (19% or 25%) is used in developing countries, and studies report high efficacy.2,3 It is more affordable, but must be applied more frequently and is associated with skin irritation.2 Lindane cream was historically prescribed, but has potential neurotoxic effects, such as numbness, tremor, and convulsions, and is now considered a second-line treatment option.2,2,5 For pregnant patients, permethrin is still considered first-line therapy, as very little is absorbed systemically, and it is rapidly detoxified.7
If topical treatments cause intolerable adverse effects or a patient is noncompliant, oral ivermectin may be used off-label.2,3 Oral ivermectin is also used in combination with topical permethrin and a keratolytic to treat crusted scabies.2 Other alternatives that are still being studied include essential oils (tea tree oil, neem oil, lippie oil, Eupatorium adenophorum oil) and turmeric.2,5 It is crucial that all the people who have been in close contact with the infected person are also treated simultaneously to avoid reinfection.2,3 Although indirect person-to person-transmission is rare, it is still common practice to recommend washing clothes and bed linens used by the infected individual.3
Symptoms should resolve during a 6-week treatment period. If not, compliance should be addressed, and reinfestation considered.7
In this case, because of a strong clinical suspicion of scabies, microscopic examination of scrapings was performed. Upon examination, mites were observed. Both the patient and her mother were prescribed permethrin cream and were instructed to wash all bedding and clothing worn during the last 3 days.
Eleanor Johnson, BA, and Yelena Dokic, BSA, are medical students at Baylor University, and Christopher Rizk, MD, is a certified dermatologist at Elite Dermatology in Houston, Texas.
1. Roncalli RA. The history of scabies in veterinary and human medicine from biblical to modern times. Vet Parasitol. 1987;25(2):193-198.
2. Heukelbach J, Feldmeier H. Scabies. Lancet. 2006;367(9524):1767-1774.
3. Chosidow O. Clinical practices. Scabies. N Engl J Med. 2006;354(16):1718-1727.
4. Hong MY, Lee CC, Chuang MC, Chao SC, Tsai MC, Chui CH. Factors related to missed diagnosis of incidental scabies infestations in patients admitted through the emergency department to inpatient services. Acad Emerg Med. 2010;17(9):958-964.
5. Mounsey KE, McCarthy JS, Walton SF. Scratching the itch: new tools to advance understanding of scabies. Trends Parasitol. 2013;29(1):35-42.
6. Dupuy A, Dehen L, Bourrat E, et al. Accuracy of standard dermoscopy for diagnosing scabies. J Am Acad Dermatol. 2007;56(1):53-62.
7. Johnston G, Sladden M. Scabies: diagnosis and treatment. BMJ. 2005;331(7517):619-622.
8. Walter B, Heukelbach J, Fengler G, Worth C, Hengge U, Feldmeier H. Comparison of dermoscopy, skin scraping, and the adhesive tape test for the diagnosis of scabies in a resource-poor setting. Arch Dermatol. 2011;147(4):468-473.