What is a key diagnostic feature of porphyria cutanea tarda?

Porphyria cutanea tarda is characterized by blisters that form on sun-exposed areas of the skin. This condition results from a deficiency of the enzyme uroporphyrinogen decarboxylase, leading to the accumulation of porphyrins that make the skin more sensitive to sunlight. When individuals with this condition are exposed to UV radiation, they develop fragile blisters that can break open and cause erosions or crusting. This specific manifestation is a hallmark of the disease, making it a key diagnostic feature.

The other choices highlight symptoms that are not typically associated with porphyria cutanea tarda. For example, Nikolsky's sign is related to conditions such as pemphigus vulgaris, where gentle pressure causes the skin to slip away from the underlying tissue. Oral lesions are characteristic of other forms of porphyria or different dermatological conditions, while systemic symptoms, like those seen in acute porphyrias, are not a main feature in the cutaneous form. Thus, the presence of blisters on sun-exposed skin serves as the principal diagnostic clue for porphyria cutanea tarda.