A 45-year-old man presents with photosensitive blistering, skin fragility, and hypertrigmented skin over the dorsum of both hands. Urine porphyrins are markedly elevated with predominant uroporphyrin. Regarding photoprotection in this patient, which statement is correct?
- A Standard chemical sunscreens with high SPF provide adequate protection
- B Photoprotection is unnecessary as the lesions are mediated by infrared radiation
- C UVA-blocking sunscreens alone are sufficient to prevent lesions
- D Protection requires visible light blocking measures as the action spectrum peaks around 400-410 nm ✓
Correct answer: D. Protection requires visible light blocking measures as the action spectrum peaks around 400-410 nm
Explanation
The action spectrum for PCT peaks in the Soret band (400-410 nm), which lies in the visible light spectrum. Standard chemical sunscreens block UV but not visible light, so they are ineffective. Physical blockers containing zinc oxide or titanium dioxide, along with window film and protective clothing, are required. This is a critical practical point in management.
Reference: Bolognia Dermatology, 4th ed.
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Written and medically reviewed by the StethoPrep medical team.