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Psoriasis — SCE Dermatology MCQ

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HardPhotobiologyPsoriasisSCE Dermatology

A patient with genetically confirmed xeroderma pigmentosum has widespread inflammatory psoriasis unresponsive to topical treatment. Which phototherapy principle is correct?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Avoid NB-UVB because defective DNA repair creates extreme UV-cancer risk

Explanation lettering: D = shown as A · E = shown as C · C = shown as D · A = shown as E

B is correct. Xeroderma pigmentosum is an absolute or near-absolute contraindication to therapeutic ultraviolet exposure because defective nucleotide-excision repair creates extreme UV mutagenesis and skin-cancer risk. Lower starting dose does not remove cumulative DNA damage, and PUVA adds rather than corrects phototoxic injury. Home phototherapy still requires specialist prescription, calibrated equipment, dosimetry and governance. NICE also advises against routine maintenance phototherapy in psoriasis. A non-UV systemic or targeted strategy should be selected with specialist attention to cancer surveillance and comorbidity.

Reference: BAD and British Photodermatology Group NB-UVB guideline: https://doi.org/10.1111/bjd.21669