Karen, originally, Tecfidera (or Dimethyl Fumerate) was licensed as a treatment for psoriasis. That could be the reason why a beneficial side effect for you is lessening of your psoriasis. It possibly makes it the best DMD for you right now.
Personally I have been plagued by auto-immune diseases. I’ve had Graves Disease, aka over-active thyroid in my early 20s. That was cured by sub-total thyroidectomy, which has meant I’ve had an underactive thyroid for many years. Obviously I’ve got MS. I’ve also had two bouts of hepatitis, the first of which was unexplained, the second caused by Tysabri. The gastroenterologist I saw and my neurologist seem to agree that there could be an auto-immune aspect to the hepatitis. I’ve also now got the beginnings of arthritic in my hands even though I’m a bit young for arthritis, this could also have an auto-immune connection.
My family have a whole host of auto-immune conditions between us, Psoriasis, Coeliac disease, CFS amongst my immediate family,
Because of my history, I’ve read quite a bit about auto-immunity. It seems that for each auto-immune disorder, there needs to be a combination of genetic predisposition, a gender and/or age factor, some environmental aspect (which can include geography), possibly a viral connection. When you put the whole lot together, if they intersect at just the right (or the wrong) point, that’s when the auto-immune disease kicks in.
There also seem to be generally groups of auto-immune diseases that go together. This is why there are many MSers who’ve had or got over-active thyroid and/or rheumatoid arthritis. They seem to go together for some reason.