What Causes Brown Spots On Legs And Burning Sensation In Left Leg?

my left leg suffers more than my right leg , but both have browness starting from the feet to half way to calf region. Some days my left leg burns when i am at work . I was scractched by a cat when i was working in an aged care home and it turned into a slight ulcer .This after the ulcer healed the start of this brown spots commenced. But i can understand why in my right leg also .