Crusted (Norwegian) Scabies: Nine-Month Course With Iatrogenic Immunosuppression

A 90-year-old female with a history of chronic obstructive pulmonary disease was referred for a 9-month history of a diffuse intensely itchy rash. Previous biopsies had demonstrated dermatitis. Her pruritus and rash progressed despite multiple therapeutic interventions, beginning with intensive topical treatments and then the initiation of systemic corticosteroids and mycophenolate mofetil. Additionally, patch testing was done with the concern of contact dermatitis and avoidance of common contact allergens was recommended. She was referred for a recalcitrant dermatitis. On physical exam, she was markedly uncomfortable (rating her itching as 10/10) and reported specific discomfort of the face and groin. She was erythrodermic (>90% of her skin). Scattered thick and hyperkeratotic crusted plaques were noted involving her scalp, face, groin and extremities (Figures 1). A mineral oil preparation demonstrated multiple mites, eggs, and feces (Figure 2). A biopsy was obtained showing superficial mixed dermal inflammation with eosinophils and numerous Sarcoptes scabiei mites (Figure 3). Oral ivermectin 200 micrograms/kg on days 1, 2, 7, 8, and 15 was initiated in addition to topical permethrin 5% daily for 7 days and then twice weekly until symptoms resolved. Additionally, prednisone was slowly tapered.

Scabies is an infestation of the skin with the parasitic arthropod Sarcoptes scabiei variety hominis with sensitization to the mite occurring several weeks before pruritus, the predominant symptom of infestation, develops.⁴ The adult mite measures between 0.2 and 0.4 mm and the mites may cause a spectrum of disease depending on the immune status of an individual.^5,6 While patients with ordinary scabies may be infested with 10-15 mites, those with crusted (Norwegian) scabies may carry up to millions of mites.⁷ An estimated 7000 mites are shed into the environment over 2 days from a patient with CS with the mite and eggs surviving for 3 and 10 days, respectively.⁵ Clinically, the patients exhibit hyperkeratotic crusts with scaly, flaky, or tightly adherent debris.⁷ While ordinary scabies typically presents with burrows in the axillae, groin, and finger webs, patients with CS may have the hyperkeratotic scaly erythema over buttocks and significant subungual debris that may be seen in other dermatitic conditions.⁵Historically, the mortality rate of CS was up to 50% secondary to bacterial sepsis.⁸ This high fatality rate may be, in part, explained by a high rate of immunosuppression associated with CS patients.⁹ In a study of 78 patients with CS, more than half had identifiable factors for immunosuppression.⁹ HIV,1 human T-lymphotrophic virus-1,¹⁰ adult T-cell leukemia/lymphoma,³ leprosy,⁹ epidermolysis bullosa,¹¹ IgA deficiency,¹² Langerhans cell histiocytosis,¹³ neutropenia,¹⁴ myelodysplasia,¹⁴ and pregnancy¹⁵ have all been reported in association with CS.As seen with our patient, iatrogenic immunosuppression has been described as a causative factor for the progression of CS. Children and adults treated with topical immunomodulators,¹⁶