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Keloid scarring — SCE Dermatology MCQ

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HardSkin of colourKeloid scarringSCE Dermatology

Since childhood, a patient has developed severe burning pain and oedema within minutes of sunlight, often without a visible eruption. Routine urine porphyrin testing is normal. Which investigation most directly tests the leading diagnosis?

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Correct answer: D — Measure plasma and erythrocyte protoporphyrin, including fractionation where available

Explanation lettering: D = shown as B · B = shown as C · C = shown as D

C is correct. Immediate painful photosensitivity from childhood with little visible rash is characteristic of erythropoietic protoporphyria or X-linked protoporphyria. Protoporphyrin is measured in plasma and erythrocytes, and fractionation helps distinguish metal-free from zinc protoporphyrin. A normal urine porphyrin result does not exclude EPP because protoporphyrin is not water soluble. Urinary porphobilinogen tests acute hepatic porphyrias with neurovisceral attacks, while isolated faecal coproporphyrin is not the direct confirmatory test here. Autoimmune serology may investigate lupus photosensitivity but is not definitive for this phenotype. Photopatch testing assesses photoallergic contact dermatitis, which produces eczema rather than immediate deep burning pain.

Reference: British Association of Dermatologists: erythropoietic and X-linked protoporphyria: https://www.bad.org.uk/pils/erythropoietic-protoporphyria-and-x-linked-dominant-protoporphyria