Boy’s progressing rash could delay surgery

THE CASE

A preoperative evaluation is requested for a 15-year-old boy who is a renal transplant patient maintained on oral mycophenolate mofetil and tacrolimus. His parents are worried that an itchy rash on his hands and feet, which has been progressing over the last 4 months, will result in postponement of his surgery.

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Etiology/Epidemiology

Crusted scabies, also known as keratotic scabies or Norwegian scabies from its first being described in Norway in the mid-1800s,¹ is a rare and severe form of infestation by Sarcoptes scabiei that most commonly affects individuals with impaired cellular immunity. It has also been reported in patients with Down syndrome and other mental or nervous system disorders.²

Clinical presentation

Crusted scabies typically presents with disseminated, ill-defined, erythematous, scaly patches, with thousands or even millions of scabies mites present in the skin. Lesions are foul smelling, with thickening of the skin, flaky crusts, and fissures developing in the affected areas. It can affect all parts of the body, but is most pronounced on the palms, soles, head, and scalp. The nails can become dystrophic and thickened. Over time and without treatment, the disease can spread to involve the entire surface of the skin.

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Unlike classic scabies, crusted scabies usually presents without intense pruritus because of the decreased cell-mediated, inflammatory response. When pruritus is present, it tends to be most prominent at nighttime. Fissures and excoriations associated with crusted scabies predispose patients to the development of secondary bacterial infections by providing a portal of entry for bacteria in already immunocompromised individuals.³

Crusted scabies is extremely contagious, and can be passed readily through physical contact. Because of the high number of scabies mites, even negligible contact (ie, through linen or clothing) with an infested person can result in infestation. However, in a person with an intact immune system, contact with crusted scabies will cause more typical scabies, with a low ectoparasite load of a few dozen live mites and intense pruritus.

Persons at increased risk for crusted scabies infection include immunocompromised individuals, such as those with HIV/AIDS, patients on systemic steroids and/or other immunosuppressive medications, those with Down syndrome, patients with neurological disorders, and the elderly.

Diagnosis

The diagnosis of crusted scabies is generally a clinical one; the lesions and history are characteristic, especially when other household members develop an itchy skin eruption with more typical findings. Well-defined burrows may not be evident on physical exam because of the abundance of scaling, flaking, and fissuring. Microscopic examination of skin scrapings usually demonstrates multiple mites. Organisms are also readily identified on dermoscopy with the characteristic “delta wing” sign, which represents the triangular shape of the mite inside a burrow. It is important to note that the absence of a delta wing sign does not exclude scabies. Often, a trial with antiscabietic medication is both diagnostic and therapeutic.

The differential diagnosis must consider psoriasis, atopic dermatitis, seborrheic dermatitis, lichen planus, pityriasis rosea, tinea, papular urticaria, systemic lupus, and Langerhans cell histiocytosis because all can present with skin findings similar to crusted scabies.

Management

Crusted scabies is treated with a combination regimen of topical permethrin or benzoyl benzoate along with oral ivermectin. It is also recommended that all close contacts be treated as well to avoid reinfestation. Patients may require multiple treatments over 2 to 3 weeks.

Next: Helping kids cope with skin disease

Patient outcome

Both parents and one sibling also complained of an itchy rash, and all members of the family were treated with 2 applications of permethrin 5% cream spaced by a week. The patient was given topical 5% permethrin daily for 7 days and oral ivermectin on days 1,2,8,9, and 15. His lesions began to regress on day 3 of treatment. His operation was postponed for 2 weeks until the completion of his treatment.

REFERENCES

1. Chan HL. Crusted (Norwegian) scabies. Australas J Dermatol. 1981;22(2):71-74. 

2. Nagsuk P, Moore R, Lopez L. A case report of crusted scabies in an adult patient with Down syndrome. Dermatol Online J. 2015;21(8).

3. Lin S, Farber J, Lado L. A case report of crusted scabies with methicillin-resistant Staphylococcus aureus bacteremia. J Am Geriatr Soc. 2009;57(9):1713–1714.

Ms Oyerinde is a 4th-year medical student at the University of Illinois College of Medicine at Chicago. Dr. Cohen, section editor for Dermcase, is professor of Pediatrics and Dermatology, Johns Hopkins University School of Medicine, Baltimore. The author and section editor have nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article. Vignettes are based on real cases that have been modified to allow the author and editor to focus on key teaching points. Images also may be edited or substituted for teaching purposes.