My dog is 10 yrs old. He has been fatigued, shivers, losing weight. Recently he has had his anklez, all four, swelling up. He has received multiple vet appointment with only thoughts on what is could be. Although the last appointment stumped the vet. His swelling is hard. He expected it to be soft. No worms, no heart worms, blood work shows lower levels in white blood cells. Any thoughts ?