In theory, any senior internist (say, one affiliated with a major medical school), willing to read up on SCLS by consulting the literature posted here under Disorder Resources, should be able to give you a definitive second opinion on your diagnosis.
The problem is that most doctors don't want to bother, because they don't get paid enough to spend all the hours needed to get themselves up to speed on such a rare illness. I was lucky to find such internists in New York and Washington DC, but they're as rare as needles in haystacks.
The other option is to make an investment in yourself -- because your insurance company may/may not cover it --and check yourself into a top medical center, like the Mayo Clinic in Rochester, MN, that has seen many patients with this and other similar conditions, will run a battery of tests during 2-3 days, study the files and notes of your own doctors, and give you a definitive diagnosis and treatment plan to take home with you.
Quite a few of the American patients in this community have done that. If interested, have your MD contact Dr. Philip Greipp at _greipp.philip@mayo.edu_
By the way, you can't go on taking Prednisone all the time, because steroids cause a lot of collateral damage. If you have SCLS, Prednisone can come in handy under strict medical supervision during episodes, but there is no proven benefit -- and there's a lot of downside -- to taking it day in and day out.