Psoriasis Exacerbation — SCE Dermatology MCQ

Correct answer: E — Streptococcal-triggered guttate exacerbation superimposed on chronic plaque psoriasis (dual pattern)

The correct answer is E, streptococcal-triggered guttate exacerbation superimposed on chronic plaque psoriasis (dual pattern). Guttate psoriasis classically follows a streptococcal throat infection, with small drop-like papules erupting acutely, and when this occurs in a patient with pre-existing chronic plaque disease the two morphologies coexist rather than one replacing the other. The positive Group A Streptococcus throat swab confirms the recognised infective trigger, and the sudden widespread onset over days (rather than the slow evolution of established plaques) is the discriminating clinical feature pointing to a new guttate flare rather than simple progression of her baseline disease. This dual pattern is well described and does not require stopping methotrexate; management focuses on treating the streptococcal infection and optimising psoriasis therapy. Why the other options are wrong: A. Pityriasis rosea: this typically follows a herald patch with oval, collarette-scaled lesions along skin cleavage lines, is linked to HHV-6/7 reactivation, and would not explain a positive streptococcal throat swab or superimposition on existing plaques. D. Normal psoriasis progression: chronic plaque psoriasis evolves gradually over months to years; a sudden widespread guttate eruption is an acute event, not the expected natural course of stable, long-standing disease. B. Drug reaction to methotrexate: methotrexate is an effective psoriasis treatment, not a recognised cause of an acute guttate flare, and the temporal link to a positive strep swab makes an infective trigger far more likely than a drug effect after five stable years. C. Secondary syphilis: this can mimic guttate psoriasis but presents with a papulosquamous rash on palms/soles, systemic symptoms, and positive serology, not a streptococcal throat culture. Key point: an acute guttate eruption on a background of stable chronic plaque psoriasis, with a positive strep throat swab, represents a streptococcal-triggered dual-pattern flare, not disease progression or an unrelated dermatosis.

Reference: NICE Clinical Knowledge Summaries (CKS), Psoriasis: Diagnosis, https://cks.nice.org.uk/topics/psoriasis/diagnosis/ - guttate psoriasis is described as an acute eruption often preceded by streptococcal throat infection, distinct from chronic plaque psoriasis, with the two patterns able to coexist.