Crusted Scabies on the Scalp Mimicking Seborrheic Dermatitis

Abstract

(See page 844 for the Photo Quiz.)Diagnosis: Crusted ScabiesAn 85-year-old woman presented to dermatologic clinic for scalp scaling of several week's duration. The clinical picture is shown as Figure 1. Skin scrapings showed multiple scabies mites under microscopic examination (Figure 2). Crusted scabies was diagnosed. We prescribed crotamition cream and 1% γ-benzene hexachoride. The hyperkeratotic plaques resolved 2 weeks later.Crusted scabies, first described by Danielson and Bock in 1848 [1], is thought to represent an inadequate host response to the Sarcoptes scabei mite, resulting in hyperinfestation with thousands of mites. The condition usually occurs in individuals with underlying immunosuppressive diseases, including human immunodeficiency virus infection, human T-cell lymphotropic virus 1 infection, and leukemia, but has also been seen in healthy patients [2]. Clinically, crusted scabies presents as a psoriasiform dermatitis with an acral distribution and an erythematous scaly eruption on the face, neck, scalp, and trunk. Crusted scabies is highly contagious and causes outbreaks among family members of the infected patient and among patients in hospital wards when inadequate preventive measures are instituted. However, the plaques of crusted scabies can sometimes be misdiagnosed as psoriasis, eczema, Darier’s disease, contact dermatitis, ichthyosis, or an adverse drug reaction. When the lesion presents on the scalp, it can simulate seborrheic dermatitis [3]. Due to the large numbers of scabies mites present in crusted scabies, using skin scraping to achieve diagnosis is easier than in classic scabies. Practitioners should keep this diagnosis in mind, especially with high-risk patients. The treatment was similar to that of classic scabies, but crust and scale removal is necessary for the scabicides to adequately penetrate.