Crusted scabies — SCE Dermatology MCQ

Correct answer: D — Oral ivermectin plus topical scabicide and contact management

The correct answer is D, oral ivermectin plus topical scabicide and contact management. This presentation, widespread hyperkeratotic crusted plaques with minimal itch in an elderly, likely immunocompromised or institutionalised patient, alongside nocturnal pruritus in contacts, is classic for crusted (Norwegian) scabies, which carries an enormous mite burden and is highly contagious. UK guidance recommends combining oral ivermectin (200 micrograms/kg, repeated doses depending on severity) with a topical scabicide such as permethrin 5 percent to achieve adequate mite kill, since crusted lesions impede topical drug penetration alone. Because transmission occurs readily to staff and other residents via direct contact and shared linen, simultaneous treatment of close contacts and environmental decontamination (laundering, isolation precautions) is essential to control the outbreak. Why the other options are wrong: C. Topical emollient therapy alone: Emollients soften keratin but have no acaricidal effect, leaving the massive mite burden untreated and infectious. A. Single application of hydrocortisone cream: Steroids suppress the host immune response and pruritus, which can worsen crusted scabies by allowing mites to proliferate further; they do not kill mites. E. Oral flucloxacillin for presumed impetigo: There is no clinical description of secondary bacterial infection here, and antibiotics do nothing to eradicate the causative mite infestation. B. Phototherapy to reduce hyperkeratosis: Phototherapy has no recognised role in scabies eradication and does not address the underlying infestation or its transmissibility. Key point: Crusted scabies with minimal itch but staff developing nocturnal pruritus signals a high mite burden requiring combined oral ivermectin and topical scabicide plus treatment of all contacts to stop institutional spread.

Reference: British Association of Dermatologists, Management of Scabies in the UK (October 2023): oral ivermectin 200 micrograms/kg with topical permethrin 5% for crusted scabies, plus contact treatment; https://cdn.bad.org.uk/uploads/2023/10/Scabies-guidance-OCT-2023.pdf