A 38-year-old man from rural India presents with a 6-month history of itchy, shiny, flat-topped papules on his dorsal hands, forearms, and lower legs. He reports that the lesions are extremely pruritic and worsen at night. On examination, there is evidence of excoriation and post-inflammatory hyperpigmentation. Oral examination reveals white lacy patches on the buccal mucosa. He denies any systemic symptoms. What is the most appropriate first-line treatment for this patient?