ABD Photodermatology and UV Effects Flashcards

PUVA therapy combines a photosensitizing psoralen with which wavelength of UV light?

Answer: UVA (320-400nm)

PUVA (psoralen + UVA) uses oral or topical psoralens photoactivated by UVA to form monoadducts and crosslinks with DNA pyrimidines, inhibiting keratinocyte and T-cell proliferation.

Solar urticaria is best classified as which type of photosensitivity disorder?

Answer: Idiopathic photodermatosis

Solar urticaria is classified as an idiopathic photodermatosis characterized by immediate urticarial wheals within minutes of sun exposure that resolve within hours.

UV-triggered lupus erythematosus flares are mediated through which mechanism?

Answer: UVB and UVA-induced keratinocyte apoptosis exposing nuclear antigens

Both UVB and UVA trigger lupus flares by inducing keratinocyte apoptosis, which translocates nuclear antigens (Ro/SSA, La/SSB) to the cell surface, amplifying autoimmune responses.

Xeroderma pigmentosum (XP) is caused by defects in which DNA repair pathway?

Answer: Nucleotide excision repair (NER)

XP is caused by mutations in NER genes (XPA through XPG, plus XPV/POLH), resulting in inability to remove UV-induced DNA photoproducts and a >1,000-fold increased skin cancer risk.

Narrowband UVB (NB-UVB) phototherapy uses which specific wavelength range?

Answer: 311-313nm

NB-UVB uses 311-313nm wavelength, which maximizes therapeutic efficacy for psoriasis, vitiligo, and atopic dermatitis while minimizing erythemogenic and carcinogenic effects.

The minimal erythema dose (MED) is defined as the smallest dose of UV radiation that produces which finding 24 hours after exposure?

Answer: Barely perceptible erythema with defined borders

The MED is the minimum UV dose producing barely perceptible erythema with clearly defined borders at the irradiated site when read 24 hours after exposure.