A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 51-year-old Indian man visits his physician because of blisters that have appeared on both hands over the past 2 months. The patient states that he works outdoors on freeways and highways, re-paving cracked or otherwise damaged roads. Three months ago, he was working with his crew and felt a sharp pain in his thighs and lower back, which he assumed was caused by the large loads of cement he was carrying to and from his truck. He has been self-medicating with over-the-counter non-steroidal anti-inflammatories, specifically naproxen, twice daily since then. He states that the naproxen relieves his back pain, but he now has blisters on both hands that worry him. On examination, the skin on his face and extremities is healthy and normal-appearing. There are a number of 2-mm-diameter hyperpigmented scars and several bullae overlying normal skin on the dorsal surface of both hands (see image). There are also several small white papules surrounding the hyperpigmented scars. Which of the following is the next step in this patient’s management?
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A
Consider removing gluten from this patient’s dietIncorrect. Gluten removal treats dermatitis herpetiformis (celiac-associated), which presents with intensely pruritic vesicles on extensor surfaces — not bullae on sun-exposed dorsal hands.
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B
Perform a stool guaiac testIncorrect. Stool guaiac evaluates GI bleeding and has no role in diagnosing photodistributed bullous skin disease.
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C
Check the patient’s urine uroporphyrin levelCorrect. Photodistributed bullae with milia and hyperpigmented scarring on dorsal hands is classic for PCT; urinary uroporphyrin confirms the diagnosis.
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D
Check the patient’s antinuclear antibody levels and renal panelIncorrect. ANA and renal panel are appropriate for systemic lupus or vasculitis, which present with malar rash, photosensitivity in a different distribution, and systemic features — not bullous disease with milia.
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E
Punch biopsy with direct immunofluorescenceIncorrect. Direct immunofluorescence is the workup for autoimmune bullous diseases such as bullous pemphigoid or pemphigus vulgaris, which do not feature milia or photodistribution on dorsal hands.
↑ Tap an answer to reveal the reasoning
Answer: C. A middle-aged man with chronic sun-exposed-skin blistering on the dorsa of his hands, hyperpigmented scars, and small white papules (milia) overlying photodistributed areas has porphyria cutanea tarda (PCT). The history of regular NSAID use is a red herring; PCT is the most common porphyria and is caused by deficient activity of uroporphyrinogen decarboxylase (UROD) in hepatocytes, with accumulation of uroporphyrinogen and related porphyrins. Triggers include alcohol, hepatitis C infection, HIV, estrogens, iron overload (hemochromatosis), and certain hepatotoxins.
The diagnostic test is measurement of urinary uroporphyrin and coproporphyrin: in PCT, urine porphyrins are markedly elevated (urine often appears tea-colored or fluoresces pink-red under Wood's lamp). Subsequent workup should include screening for HCV, HIV, iron studies (ferritin, transferrin saturation), and HFE mutation testing because of the strong association with iron overload.
Treatment involves trigger avoidance (alcohol, estrogens, sun), repeated phlebotomy to reduce hepatic iron, and low-dose hydroxychloroquine.
**Why each option:**
**A.** Gluten removal treats dermatitis herpetiformis (celiac-associated), which presents with intensely pruritic vesicles on extensor surfaces — not bullae on sun-exposed dorsal hands.
**B.** Stool guaiac evaluates GI bleeding and has no role in diagnosing photodistributed bullous skin disease.
**C.** Correct. Photodistributed bullae with milia and hyperpigmented scarring on dorsal hands is classic for PCT; urinary uroporphyrin confirms the diagnosis.
**D.** ANA and renal panel are appropriate for systemic lupus or vasculitis, which present with malar rash, photosensitivity in a different distribution, and systemic features — not bullous disease with milia.