You will note that there are 565 replies to this thread.
http://www.medhelp.org/posts/Hepatitis-C/Long-term-side-effects-of-interferon/show/866107?page=1
If you use the HCV board search engine (not the entire board, but one for the hep c forum) you will find many such threads.
You can also type in your symptoms to further refine your search, such as joint inflammation. Part of the issue is that HCV can cause this, or post TX issues, or externally caused genetic RA, or other causes. It is hard to directly prove one cause.
You may be able to document your issues this way. I can also tell you that many people are on disability due to this, and so there may be some legal precedents where people have already been granted the disability based upon similar complaints.
My understanding is that the Mayo clinic is calling it PIS; post interferon syndrome. The "syndrome" part of that label kind of indicates that they are aware there is an issue, but the do not have adequate diagnosing tools and they are striving to work on cause and cure. Many doctors are surprised at this outcome in spite (as you will see if you read the thread and others like it) that yours is not an isolated case.
best,
Willy