Mpox — DTM&H MCQ

Correct answer: A — PCR from lesion swabs for mpox virus

The correct answer is A, PCR from lesion swabs for mpox virus. The clinical picture of fever, inguinal lymphadenopathy and umbilicated genital and perianal lesions at different stages, in a returning traveller from an endemic African region, is classic for mpox. UKHSA guidance specifies that viral swabs in transport medium should be taken from the base of a vesicle or blister (or open sore) for mpox PCR, as this is the definitive diagnostic test. Umbilication and lesions at multiple stages simultaneously reflect the crops of pox-like lesions typical of mpox, distinguishing it from varicella (uniform stage) and from bacterial or treponemal ulcers. PCR of lesion material has the highest sensitivity and specificity and directly confirms orthopoxvirus infection. Why the other options are wrong: D. Blood film for malaria species as the diagnostic lesion test: malaria causes fever but never produces umbilicated skin or genital lesions, so a blood film cannot explain the rash and lymphadenopathy described. E. Urine microscopy for schistosome eggs: schistosomiasis causes haematuria or Katayama fever, not vesiculopustular umbilicated genital lesions with lymphadenopathy. B. Stool ova and parasite microscopy: intestinal parasites do not cause umbilicated skin lesions or acute lymphadenopathy of this pattern. C. Serum amylase for mumps: mumps causes parotitis, not genital ulceration, and amylase is a nonspecific marker unrelated to skin lesion diagnosis. Key point: Umbilicated skin and mucosal lesions at different stages with lymphadenopathy in a traveller should prompt lesion swab PCR for mpox, as this is the confirmatory test recommended in UK guidance.

Reference: UKHSA, Mpox (monkeypox): guidance, GOV.UK, cited via University Hospitals of North Midlands pathology guidance: viral swabs in viral transport medium from the base of a vesicle/blister requested for mpox PCR (https://www.uhnm.nhs.uk/our-services/pathology/tests/mpox-monkeypox/)