So I have been keeping frogs/toads for eight or nine years, and have had my FBT for about a year now. I adopted him because he has a deformed back leg and was starving in the pet store (it's basically just a stump with two toes sticking out of it).
Up until tonight he's had no health issues. A couple weeks ago he stopped eating normally, but I assumed he was just picking up on the seasons changing since he would still occasionally eat and has not lost weight. Until tonight he's been active and strong as well.

So tonight I noticed he was moving oddly and put him in a cup to observe him. He is listing very heavily toward the side with the deformed leg and doesn't seem to be able to move the arm on that side properly. When he tries to hop, he sometimes flips over and has trouble righting himself. Still very active and alert, no irregularities on his skin, not swollen or anything. As I'm observing him, it seems like the weakness and mobility issues come and go fairly quickly.

Have you guys ever seen anything like this? Do you think it's a congenital or neurological thing? Any suggestions? I can't think of anything toxic he could have come into contact with, and he's acting way more alert and active than I'd expect from an infection bad enough to cause all of this.

Also, I'm in the process of draining his enclosure low enough that he couldn't drown if he flipped over.