Scabies is caused by cutaneous ectoparasitic infection by the mite Sarcoptes scabiei var hominis. The infection is highly contagious via direct skin-to-skin contact or indirectly through infested bedding, clothing or fomites.1,2 Scabies occurs at all ages, in all ethnic groups, and at all socioeconomic levels.1 Analysis by the Global Burden of Disease estimates that 200 million individuals have been infected with scabies worldwide. The World Health Organization has declared scabies a neglected tropical disease.3
Crusted scabies is a severe and rare form of scabies, with hyperinfestation of thousands to millions of mites, and more commonly is associated with immunosuppressed states, including HIV and hematologic malignancies.1,2,4 Crusted scabies has a high mortality rate due to sepsis when left untreated.3,5
Occasionally, iatrogenic immunosuppression contributes to the development of crusted scabies.1,2 Iatrogenic immunosuppression leading to crusted scabies most commonly occurs secondary to immunosuppression after bone marrow or solid organ transplantation.6 Less often, crusted scabies is caused by iatrogenic immunosuppression from other clinical scenarios.1,2
We describe a patient with iatrogenic immunosuppression due to azathioprine-induced myelosuppression for the treatment of granulomatosis with polyangiitis (GPA) who developed crusted scabies that clinically presented as erythroderma. Crusted scabies should be included in the differential diagnosis of erythroderma, especially in the setting of iatrogenic immunosuppression, for timely and appropriate management.
An 84-year-old man presented with worsening pruritus, erythema, and thick yellow scale that progressed to erythroderma over the last 2 weeks. He was diagnosed with GPA 6 months prior to presentation and was treated with azathioprine 150 mg/d, prednisone 10 mg/d, and sulfamethoxazole 800 mg plus trimethoprim 160 mg twice weekly for prophylaxis against Pneumocystis jirovecii pneumonia.
Three weeks prior to presentation, the patient was hospitalized for pancytopenia attributed to azathioprine-induced myelosuppression (hemoglobin, 6.1 g/dL [reference range, 13.5–18.0 g/dL]; hematocrit, 17.5% [reference range, 42%–52%]; white blood cell count, 1.66×103/μL [reference range, 4.0–10.5×103/μL]; platelet count, 146×103/μL [reference range, 150–450×103/μL]; absolute neutrophil count, 1.29×103/μL [reference range, 1.4–6.5×103/μL]). He was transferred to a skilled nursing facility after discharge and referred to dermatology for evaluation of the worsening pruritic rash.
At the current presentation, the patient denied close contact with anyone who had a similar rash at home or at the skilled nursing facility. Physical examination revealed diffuse erythroderma with yellow scale on the scalp, trunk, arms, and legs (Figure 1). The palms showed scattered 2- to 3-mm pustules. The mucosal surfaces did not have lesions. A punch biopsy of a pustule from the right arm revealed focal spongiosis, parakeratosis, and acanthosis, as well as a perivascular and interstitial mixed inflammatory infiltrate with lymphocytes and eosinophils. Organisms morphologically compatible with scabies were found in the stratum corneum (Figure 2). Another punch biopsy of a pustule from the right arm was performed for direct immunofluorescence (DIF) and was negative for immunoglobulin deposition. Mineral oil preparation from pustules on the palm was positive for mites.