Have you tried prednisone? It's a steroid anti-inflamatory that can bring down the inflamation. i have severe low back pain associated with a bulging disc and degenerative disc disease (I'm only 27!) with pain running down both legs and I gained incredible relief from prednisone. I had to take 60 mg a day for effective relief. It's not a great drug to be on for extended periods of time. It can effect your bones in a negative way and the skin also. But I was on a 10 day taper. 60 mg for 7 days and then 40 mg for two days and 20 mg for the last day.
My pain came back but that week was heaven. Maybe from there the doctors can get a better handle on his pain.
Have you tried narcotics? Mild perocet also help my pain.
I wish you and your son the best of luck. Chronic pain is miserable.
There are anti-depressants out there that have also shown improvement in people with chronic pain.