1) A 66-year-old woman reports itching and flaking of the face and scalp for the past several months. She has tried multiple dandruff shampoos and over-the-counter lotions without relief. She has lost 4.5 kg unintentionally during the past 6 months. Physical examination reveals yellowish scaling and erythema of her nasolabial creases and the skin around her eyebrows (see figure below). She also has greasy scaling of the scalp. Which one of the following tests is most appropriate for this patient? *
