andrew someone paged me to this post today, sorry just seeing it, i'm not around everyday anymore.
gee, the video was rough to see.

mim has cardiac issues, can you talk to your vet about this possibility of this being ischemic neuromyopathy?* was really the first thing i thought of as i was watching the video. this doesn't look like arthritis or diabetic neuropathy to me (and the time frame is wrong for diabetic neuropathy, doesn't make sense that he would develop it now at this point when so regulated). how are his electrolyte levels? (not hypokalemic (low potassium) or hypocalcemic right?) what was the time frame from starting raw to this starting... is there a link? are you sure he is getting enough thiamine?
hope your vet is able to help, really don't like seeing mim like that.
~jojo
*Ischemic Neuromyopathy occurs in cats with cardiomyopathy, subsequent to thrombosis of the caudal aorta or its principal branches. The ischemic injury to both muscle and peripheral nerve is produced by collateral circulation vasoconstriction induced by substances such as serotonin and thromboxane A2 released by platelets trapped in the thrombus.
~from 2008 WSAVA proceeding
http://www.vin.com/proceedings/Proceedi ... &O=Generic