Its pretty much a judgement call by the doc. He will evaluate your pain, blood work, etc. There must be a specific diagnosis, not just "joint pain" or "fatigue." I think a diagnosis from a specialist (such as a rheumatologist) would carry more weight than a gen. practitioner.
i am from canada and we have to have a specialist make the official diagnosis.then its fill out all the forms and wait. im my case i have ra and i am declared permanent disabled.
I am also from Canada, diagnosed with lupus. After filling out all the forms, and getting my doctor and internist to add their comments, I was finally accepted and declared disabled. It was a long wait though.