Chronic plaque psoriasis — SCE Dermatology MCQ

Correct answer: B — Combined potent corticosteroid and vitamin D analogue

The correct answer is B, combined potent corticosteroid and vitamin D analogue. This man has limited chronic plaque psoriasis (well-demarcated, silvery-scaled plaques on extensor surfaces and lower back, 4% body surface area, no nail or joint involvement) that has failed to settle with emollients alone. NICE guidance identifies a once-daily potent corticosteroid combined with a once-daily vitamin D analogue (applied separately, up to four weeks) as the recommended first-line topical step-up for trunk and limb plaque psoriasis once emollients alone are insufficient. This combination reduces scale and erythema faster than either agent alone while limiting the corticosteroid exposure needed, matching this patient's limited, uncomplicated presentation. Why the other options are wrong: E. Oral methotrexate as first-line therapy: Systemic therapy is reserved for extensive (typically over 10% body surface area), functionally or psychologically disabling, or treatment-resistant psoriasis, or when there is psoriatic arthritis; none apply here. D. Topical fusidic acid to plaques: This is an antibacterial for infected skin lesions; there are no signs of secondary bacterial infection, and it has no effect on psoriatic plaque pathology. C. Permethrin cream repeated in one week: This is scabicide treatment for scabies, which presents with intense itch and burrows in finger webs, not well-demarcated silvery plaques on extensor surfaces. A. Topical antifungal cream for 4 weeks: The distribution and morphology are typical of psoriasis, not dermatophyte infection, which would show an active advancing edge with central clearing rather than uniform silvery scale. Key point: Once emollients fail in limited plaque psoriasis, step up to a once-daily combined potent corticosteroid plus vitamin D analogue before considering systemic agents.

Reference: NICE Clinical Knowledge Summary / NG153: Psoriasis - Management. Recommends a potent corticosteroid applied once daily plus a vitamin D or vitamin D analogue applied once daily (separately) for up to 4 weeks as first-line topical treatment for trunk/limb psoriasis. cks.nice.org.uk/topics/psoriasis/