Q. A 62-year-old woman presents to the clinic with a one-year history of darkening and swelling of her lower legs. She often feels a heavy, aching sensation in her legs, especially after prolonged standing. On physical examination, both her lower legs exhibit noticeable hyperpigmentation, particularly around the ankles. The skin over these areas is firm and indurated, and there is pitting edema noted up to the mid-calf region. No open ulcers are observed, but a few dilated superficial veins are visible on both legs. A Doppler ultrasound of her lower extremities reveals reflux in both superficial and deep veins, especially pronounced during the Valsalva maneuver. Routine blood work, including a complete blood count, kidney and liver function tests, is within normal limits. Her ankle-brachial index (ABI) is 1.1, indicating normal arterial perfusion to the legs. What would be the most likely diagnosis?