Darkening of the skin around the ankles may indicate chronic venous reflux disease, a condition of the vein valves, detectable by ultrasound.
Over time, leakage of the blood into the area surrounding the veins can cause tissue to die. The resulting pooling of blood in the tissue causes a darkening of the skin. It is at this stage that the skin is actually stained by your own blood. This is also known as venous stasis skin changes, skin hyperpigmentation, or venous stasis dermatitis because the skin is often inflamed, itchy and eczema-like. This is most frequently caused by venous reflux, an underlying condition that can be treated. When skin changes like these are present, the condition is termed chronic venous insufficiency. Over time, the skin condition may worsen and the skin may become darker, firm to touch, scaly and itchy, and the skin may break down causing a venous leg ulcer.