Simon

Thank goodness for second opinions.
After nearly throwing in the towel with Simon, I took him to another vet for a second opinion - one that came highly recommended. More blood work, more examinations, more head-scratching - until on a hunch they looked at a smear of his blood under a microscope, and Voila! - a parasite in his blood! It seems he is badly infected with a tick-borne parasite that is rapidly multiplying in his blood, causing the joint pain, malaise, severe weight loss, fever and more. The bad news is that he is acutely infected, more so than this vet has ever seen in a cat - but the good news is that the condition usually is treatable with doxycycline, which we started him on immediately. I again have hope that he's going to pull through this and once again be my curious cat who loves lying in sunny window wells and chasing his sister, Sasha.
Meanwhile, another gorgeous day here in central Wisconsin. A mama duck and thirteen ducklings were crossing the road in front of our house - very cute.