Test your diagnostic skills in our regular dermatology quiz. What is the cause of this sharply marginated, photodistributed rash?
A 48-year-old woman presents with a three-week history of pruritic erythema on the dorsal aspect of her forearms and hands (Figures 1a and b) and feet (Figure 2). The eruption is sharply marginated, hyperpigmented and hyperkeratotic. Over the past 24 hours, she has developed bilateral ankle and foot oedema surmounted by tense bullae (Figure 2). The eruption is photodistributed; there is no rash on any other area of her skin.