Scabies — SCE Dermatology MCQ
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Correct answer: A — Diagnose scabies clinically and treat empirically based on the classic history and distribution
The correct answer is A, diagnose scabies clinically and treat empirically based on the classic history and distribution. Scabies is a clinical diagnosis in the vast majority of cases: nocturnal pruritus, a symptomatic close contact (partner), and the classic distribution of finger webs, wrists and genitalia are highly specific for infestation with Sarcoptes scabiei. Dermoscopy and microscopy have imperfect sensitivity because classic scabies carries only a handful of mites on the whole body, so a negative scope does not exclude the diagnosis. UK guidance recommends treating on clinical grounds when the history and examination are typical, rather than delaying for confirmatory testing, because delay prolongs transmission to contacts and household members. Why the other options are wrong: C. Perform a skin biopsy: biopsy is unnecessary and invasive for a condition that is diagnosed clinically; it is reserved for atypical or crusted scabies where the diagnosis remains uncertain after standard assessment. E. Prescribe topical corticosteroid only: steroids suppress the itch and inflammatory response without killing the mite, allowing continued transmission and risking masked or worsened infestation (incognito scabies). D. Wait for symptoms to worsen before treating: deliberately delaying treatment increases mite burden, prolongs symptoms, and increases the risk of spread to other contacts; this is never appropriate management. B. Order blood tests for eosinophilia: eosinophilia is nonspecific, can be absent in scabies, and does not confirm or exclude the diagnosis, so it adds no diagnostic value here. Key point: a negative scrape or dermoscopy does not exclude scabies; a classic history, distribution and affected contact are sufficient to diagnose and treat empirically.
Reference: NICE Clinical Knowledge Summaries (CKS), Scabies, cks.nice.org.uk/topics/scabies (accessed 2024)