Papules on the soles of the feet

Scabies is caused by the Sarcoptes scabiei mite and is typically transmitted by direct contact.1 The intense pruritus with which it typically presents can be so debilitating that the disease is embedded in historic accounts, from the Ancient Greek physicians...

Submit your diagnosis to see full explanation.

Scabies is caused by the Sarcoptes scabiei mite and is typically transmitted by direct contact.¹ The intense pruritus with which it typically presents can be so debilitating that the disease is embedded in historic accounts, from the Ancient Greek physicians to the French revolutionaries, who supposedly had “the itch.”² Although it is primarily a cutaneous infection, the potential for secondary bacterial skin infection links scabies to further complications such as lymphadenopathy, acute poststreptococcal glomerulonephritis, and rheumatic fever.³

The prevalence of scabies is higher in children than in adolescents and adults.⁴ The Global Burden of Disease Study of 2010 estimated a worldwide prevalence of 100 million cases, with the high disease burden in the Pacific region.⁴ Few quality, population-based studies are available despite the high disease burden; scabies was added to the World Health Organization’s list of neglected tropical diseases in 2013.^3,4

Populations at increased risk include children, the elderly, and immunocompromised individuals.^1,4 Scabies is also associated with malnutrition, reduced access to health care, poverty, and domestic crowding.^1,4

Clinically, patients have an intense pruritus that typically spares the head and neck.⁵ The pruritus can occur within 4 to 6 weeks of a first infestation, or within 24 hours of a reinfestation.⁵ A hyperinfestation of scabies may indicate an immunocompromised state.⁵ Lesions occur at the sites of mite infestation but can also result from hypersensitivity to mites or secondary to chronic rubbing and scratching.⁵ Lesions typically appear as erythematous papules (and sometimes pustules) and burrows. Intraepidermal burrows and papules may be visible as linear or serpiginous ridges commonly found in the finger webs, wrist flexures, elbows, or armpits, or on the breasts or in the genital region, and in the palms and soles of infants.^1,5 Patients may be aware of similar symptoms in other household members.⁵

Histologically, primary lesions are characterized by epidermal hyperkeratosis, acanthosis, spongiotic edema, and vesiculation.⁶ Dermal perivascular and diffuse cell infiltrates are mainly composed of mononuclear cells and sometimes eosinophilic granulocytes.⁶ Secondary lesions have acanthuses and a perivascular inflammatory infiltrate composed of mononuclear cells.⁶ The number of circulating eosinophils and serum immunoglobulin E concentrations may correlate with the severity of the skin lesions.⁶ However, the most diagnostic and specific findings are the visualization of the mites, ova, or scybala (mite feces) in the stratum corneum.

The differential diagnosis is broad and ranges from localized or generalized pruritus to eczema, delusions of parasitosis, adverse drug reactions, allergic contact dermatitis, or pruritus secondary to a metabolic condition.⁵ The intense pruritus can lead to excoriation and secondary bacterial infection, resulting in impetigo.¹

Diagnosis is reached clinically and can be confirmed by visualization of the mites, mite eggs, or mite feces through microscopy (this can be easily and cheaply performed in any office setting with a basic light microscope).⁵ Microscopy can be performed by lightly scraping an area of burrows with a #15 blade, wiping the blade on a glass slide containing a layer of mineral oil, placing a coverslip over the slide, and viewing it under the microscope. An evidence-based diagnostic criteria is currently being formulated by the International Alliance for the Control of Scabies (Melbourne, Australia).⁴

Several treatment options are effective; the standard is to treat individuals and household members at the same time.⁴ Topical treatment with 5% permethrin, 10% or 25% benzyl benzoate, or 1% benzene hexachloride is effective, although drawbacks include expense of the medication and compliance with application over extensive body surface areas.^4,5 In most areas, the first-line therapy is topical treatment with 5% permethrin. Permethrin should be applied on all skin from the neck down, and should not be washed off for at least 12 hours; this routine should be repeated 7 days later. Alternatively, 2 doses of oral ivermectin (200 mg/kg) can also be effective (first dose on day 1 and second dose on day 14).⁵ Mass administration of a topical treatment or oral medication such as ivermectin to an entire community has been effective in treating outbreaks in remote areas and localized outbreaks in institutions.⁴ However, treatment expense remains a drawback and the lack of safety data for ivermectin prevents use in young children and pregnant women.⁴

Pruritus can persist for several weeks after mite eradication.⁵ The rate of reinfestation through community or household contacts remains high and control measures such as laundering all bed linen must be implemented.⁴

In this case, scabies was suspected because multiple family members appeared to have the same rash. A skin scraping was performed, and a mite was visualized under microscopy. The patient and all household members were treated with permethrin, which led to the resolution of the rash.

Laraib Safeer, BS, is a medical student at the Baylor College of Medicine, and Christopher Rizk, MD, is a dermatology resident at the Baylor College of Medicine.

References

1. Banerji A. Scabies. Paediatr Child Health. 2015;20:395-402.
2. Weisshaar E, König A, Diepgen TL, Eckart WU. About itching and scabies. Pruritis in medical history—from the ancient world to the French revolution [article in German]. Hautarzt. 2008;59:1000-1006.
3. Thomas J, Peterson GM, Walton SF, Carson CF, Naunton M, Kavya EB. Scabies: an ancient global disease with a need for new therapies. BMC Infect Dis. 2015;15:250.
4. Romani L, Steer AC, Whitfeld MJ, Kaldor JM. Prevalence of scabies and impetigo worldwide: a systematic review. Lancet Infect Dis. 2015;15:960-967.
5. Wolff K, Johnson RA, Saavedra AP, Roh EK, eds. Fitzpatrick’s Color Atlas and Synopsis of Clinical Dermatology. 8th ed. New York, NY: McGraw-Hill Education; 2017.
6. Falk ES, Eide TJ. Histologic and clinical findings in human scabies. Int J Dermatol. 1981;20:600-605.