A 38-year-old woman presents with a 4-month history of recurring blistering lesions on her hands, forearms, and face. Physical examination reveals multiple tense blisters and erosions with surrounding erythema and several scars in these areas as shown below. 
Laboratory tests show elevated liver enzymes and she does report drinking a moderate amount of alcohol. Which of the following is the most likely diagnosis?
A. Bullous pemphigoid
B. Dermatitis herpetiformis
C. Porphyria cutanea tarda
D. Pemphigus vulgaris
E. Erythema multiforme
Rationale: Understanding, categorizing, and differentiating blistering disorders is based on clinical symptoms, biopsy findings, direct immunofluorescence (DIF) results, as well as laboratory results such as antibody testing. The question stem excludes biopsy results, DIF, and antibody testing which can make it difficult to diagnose for certain; however, given the clinical location and age of the patient, the most likely diagnosis of the above choices can be recognized.
Correct answer: C. Porphyria cutanea tarda
Porphyria cutanea tarda is associated with a uroporphyrinogen deaminase (UROD) deficiency and presents with photosensitive blistering lesions typically located on sun-exposed areas like the hands and face. Facial hypertrichosis and hyperpigmentation is common. Elevated liver enzymes and increased porphyrins in the urine are characteristic. Treatment includes phlebotomy and low-dose hydroxychloroquine.
Incorrect answers:
A. Bullous pemphigoid typically presents with tense blisters on the trunk and extremities and is more commonly observed in the elderly.
B. Dermatitis Herpetiformis presents with pruritic, grouped vesicles, typically on extensor surfaces such as the elbows, knees, and buttocks. DH is associated with gluten sensitivity/Celiac disease.
D. Pemphigus vulgaris presents with flaccid blisters and erosions on mucous membranes and skin. It is characterized by intraepidermal blistering and most patients have oral involvement.
E. Erythema multiforme typically presents with targetoid lesions on the skin and is often triggered by infections or medications.
Additional reading at Fitzpatrick's Dermatology Chapter 124: The Porphyrias
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