Photodermatoses and Disorders of Keratinization (Ichthyoses, PRP) MCQs

Dermatology · 15 free questions with answers & explanations.

1. Polymorphic light eruption (PLE) is the most common idiopathic photodermatosis. Its action spectrum most commonly lies in:
2. Xeroderma pigmentosum (XP) is an autosomal recessive genodermatosis with markedly increased skin cancer risk. The primary defect is in:
3. Lamellar ichthyosis (autosomal recessive congenital ichthyosis) presents at birth as a 'collodion baby'. The gene most commonly mutated in the classic lamellar subtype encodes:
4. Pityriasis rubra pilaris (PRP) is a papulosquamous disorder. The PATHOGNOMONIC clinical hallmark is:
5. Xeroderma pigmentosum (XP) predisposes to early skin cancers due to defective repair of UV-induced DNA damage. Which specific DNA repair pathway is defective in the most common XP complementation groups (XP-A to XP-G)?
6. Pityriasis rubra pilaris (PRP) Type I (adult classic) has a distinguishing clinical sign that helps differentiate it from extensive plaque psoriasis. Which feature is characteristic of PRP?
7. X-linked ichthyosis (XLI) differs from ichthyosis vulgaris clinically and biochemically. Which deficiency characterises XLI and explains its pathogenesis?
8. Polymorphous light eruption (PMLE) is the most common photodermatosis. Which of the following correctly describes its immunopathogenesis?
9. A child with xeroderma pigmentosum (XP) has markedly increased sensitivity to UV radiation and a 1000-fold increased risk of skin cancer. The fundamental molecular defect in the most common form (XP group A) involves failure of which DNA repair pathway?
10. Pityriasis rubra pilaris (PRP) Type I (classic adult) is distinguished from psoriasis by which clinical feature?
11. Lamellar ichthyosis is caused by a defect in which enzyme, and its histological hallmark is:
12. Polymorphic light eruption (PMLE) is the most common photodermatosis. Its pathomechanism involves:
13. A neonate is born encased in a tight, shiny, parchment-like membrane that cracks and fissures on flexion. The membrane peels off in the first few weeks of life, and the subsequent course determines the underlying ichthyosis type. What is this neonatal presentation called, and the most common transient ultimate outcome?
14. A patient presents with salmon-coloured plaques with islands of normal skin (skip areas) on the trunk and erythroderma. Palmoplantar keratoderma is present. Follicular keratotic papules (nutmeg-grater texture) are seen on the dorsa of fingers. This is type I classic adult pityriasis rubra pilaris (PRP). The key histological feature that differentiates PRP from psoriasis is:
15. A patient with polymorphic light eruption (PLE) asks about long-term preventive measures. The mechanism by which hardening (photohardening) therapy prevents PLE flares in subsequent summer seasons is: