Ease Into Prep with a USMLE^® Step 2 CK Question of the Day

The correct answer is E. Porphyria cutanea tarda is the most common of the porphyrias. It causes chronic blistering and crusting lesions on sun-exposed skin. The defective enzyme in heme synthesis is uroporphyrinogen decarboxylase. Precipitating factors include iron (even in normal amounts in some cases), estrogen use, alcohol use, and chronic hepatitis C infection. Skin biopsy can be helpful but is usually not completely specific (the "caterpillar bodies" in the question stem are clumps of basement membrane material). Porphyrin analyses demonstrate the findings in the question stem.

Acute intermittent porphyria (choice A) is one of the more common forms of porphyria and typically presents with severe abdominal pain.

Delta-aminolevulinic acid dehydratase deficiency (choice B) is a rare form of porphyria that can cause abdominal pain and hemolysis.

Erythropoietic porphyria (choice C) is one of the more common forms of porphyria and typically presents in childhood or infancy with acute, rather than chronic, photosensitivity with pain and swelling after sunlight exposure.

Hereditary coproporphyria (choice D) is a rare porphyria than presents with abdominal pain.