ABD ABD Photodermatology and UV Effects 2

Question 1

Porphyria cutanea tarda (PCT) is caused by deficiency of which enzyme in the heme biosynthesis pathway?

Accepted Answer

Uroporphyrinogen decarboxylase (UROD)

Answer

PCT results from deficiency of uroporphyrinogen decarboxylase (UROD), causing accumulation of uroporphyrins that absorb light and generate reactive oxygen species in the skin.

Question 2

Erythropoietic protoporphyria (EPP), the most painful photosensitivity disorder, is classically caused by mutations in which gene?

Accepted Answer

FECH (ferrochelatase)

Answer

Classic autosomal recessive EPP is caused by loss-of-function mutations in FECH (ferrochelatase), the terminal enzyme of heme synthesis, causing protoporphyrin IX accumulation.

Question 3

Which SPF value blocks approximately 97% of UVB radiation?

Accepted Answer

SPF 30

Answer

SPF 30 blocks approximately 97% of UVB radiation; SPF 15 blocks 93%, SPF 50 blocks 98%, and SPF 100 blocks 99%, showing diminishing returns at higher values.

Question 4

Chronic actinic dermatitis (CAD) is characterized by which predominant lymphocyte subset on histopathology?

Accepted Answer

CD8+ cytotoxic T cells

Answer

CAD characteristically shows a CD8+ cytotoxic T-cell predominant infiltrate, which distinguishes it from other eczematous dermatoses that are predominantly CD4+.

Question 5

UVB radiation (280-315nm) is primarily responsible for photocarcinogenesis through which mechanism?

Accepted Answer

Direct DNA damage forming cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts

Answer

UVB causes direct DNA damage by forming cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts between adjacent pyrimidines, producing C→T transition mutations.

American Board of Dermatology (ABD) Practice Test

American Board of Dermatology (ABD) Practice Test

ABD ABD Photodermatology and UV Effects 2