"I'm BAAACK!"

And THIS would be how Kittyboy looks with no spots whatsoever, astride his valiant steed in Dr. L's office! "Ha HA, with my noble donkey I shall conquer the world once more!"
No spots. No remaining arthritis (after two days of having to carry him, very carefully, anywhere he wished to go, and not touch or move his legs for fear of hurting him). No fever. No more Tylenol or Motrin unless his joints are aching (they're still healing, after all). Just Allegra and followup visits.
And Dr. L has managed to explain, to the one who got a C in Baby Bio her freshman year of college, what the heck serum-like sickness is. There's something that the immune system recognizes as a foreign substance - a virus, a medication, some random THING. The immune system gets way over-enthused in its attack of said substance and lots and LOTS of antibodies attach to whatever it is. So many antibodies bind to the substance that the body has a really hard time then dealing with it and flushing it out, which causes a lot of problems - hives, fever, swollen and aching joints, known as reactive arthritis. That's basically what happened. Will it happen again? No way to know. We're avoiding "cillin" antibiotics like the plague, because there's no way to know if the amoxicillin was the triggering substance or not.
But the important thing is... heeee's BAAACK!