A 43-year-old women presents with a long-standing history of pain at the tip of her right non-dominant middle finger. Pain is exacerbated by cold weather. She denies systemic symptoms or preceding trauma. She has seen a number of physicians but no formal diagnosis as been made. Physical examination reveals no distinct mass or color change. Pain is reproduced by palpating over the ulnar nail bed of her distal middle finger. Radiographs and routine laboratory results are within normal limits. MRI images are shown in Figures A-C. What is the most likely diagnosis?