What Would Cause A 69 Year Old Man Feet To

What would cause a 69 Year old man feet to swell really big, lose his ability to put one foot in front of the other so he can't walk and slurred speech? He has a mental disorder that's been going on for 20 years or more but these other physical symptom's just started in the last couple of weeks. He had all kinds of blood work done but nothings showed up in it. Could it be the on set of dementia, he knows everything thats going on , his brain seems as sharp as ever about remembering things. But he has real bad compulsions that the Dr's have been giving his medicine for for quite a few years and nothing has ever helped them. So any ideas of what could be going on with him, Mom had to put him in a Senior care place for now to see if they can help him walk again. Thanks,Penny