Diagnostic dilemma: crusted scabies superimposed on psoriatic erythroderma in a patient with acquired immunodeficiency syndrome

A 45-year-old man with AIDS presented with extensive erythema and scaling involving the face, trunk, and upper and lower extremities, and mild nail dystrophy. The patient had been diagnosed with psoriasis 2 years previously, and at the time of presentation was using emollients and topical corticosteroid creams with little improvement. He was receiving zidovudine, lamivudine, trimethoprim/sulfamethoxazole, acyclovir, rifabutin, and hydroxyzine. Pertinent laboratory data included CD4 lymphocytes (10 cells/mm(3)), viral load (32,000 copies per mL) white blood cell count (3.4 x 10(3)/microL), hemoglobin (13.5 g/dL), and platelets (204 x 10(3)/microL). Because of the extensive eruption and lack of response to topical agents, the patient was started on acitretin 25 mg daily. The patient had shown no signs of improvement 4 weeks later and was noted to have brownish gray crusted plaques involving the beard area, neck, upper part of the back, arms, trunk, genitals, and thighs in addition to his erythroderma (Figure 1 and Figure 2). Microscopic examination of scales from the upper part of the back revealed numerous scabies mites and eggs. He was then treated with lindane shampoo on the scalp and beard area and permethrin 5% cream to the body. The patient returned 2 weeks later with some improvement after thrice-weekly applications of this regimen; however, scrapings from the trunk once again revealed live scabies mites. Microscopic examination of scales that had fallen on the examination table revealed multiple mites and eggs. The patient was then given permethrin 5% cream, which he applied 3 times a week for 2 weeks, and 1 dose of oral ivermectin, 200 micro/kg. This resulted in a marked decrease in crusting and scaling. With resolution of the scabies lesions, the patient displayed marked erythema and scaling of the trunk and extremities consistent with generalized psoriasis (Figure 3). Treatment with acitretin resulted in gradual resolution of the erythroderma. A few months later, the patient presented with nodules on the upper part of the back, which on biopsy revealed a scabies mite (Figure 4).