CASE
An 89-year-old male presented with a mildly pruritic erythematous patch on his right knee that had slowly extended over the past 2 years. The patch had not responded to topical corticosteroids he had been using for existing psoriasis on the knee. The history was otherwise unremarkable. On examination, silvery oval plaques were visible on the patient's left knee and elbows. Examination of the right knee demonstrated a large, well-demarcated patch with residual erythema and central clearing (Figure 1).
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