You are seeing a 43-year-old female patient in a primary care setting who has presented with a rash. On examination you note the presence of a violet shiny flat-topped papule with white streaks on the flexor surfaces of the wrists, forearms and legs. The patient informs you the rash is often accompanied with blisters. A biopsy is taken and it is characterised by a saw-tooth pattern of epidermal hyperplasia and vacuolar alteration of the basal layer of the epidermis. What is the most likely diagnosis?