That looks like it might be gout. He needs to go to a good reptile vet. I don't think the prognosis is very good nor do vets really understand how to treat them or even effectively test for it. My understanding is that it is very very painful.
The trouble is that blood work is inconclusive. I believe the only accurate way to diagnose is to take a biopsy and actually find the crystals in the body tissues. Gout in reptiles is usually caused by kidney problems stemming from dehydrations, starvation or antibiotic use, especially on a dehydrated animal. Improper temperatures affects the ability of the kidneys to filter out uric acid of the blood. Improper diet is also a contributing factor.
Gout is one of the reasons I think every single chameleon needs an automatic mister since chronic low level dehydration causes kidney failure, and poor kidney function is a cause of gout.