I’m so sorry for your father’s diagnosis of this . It is almost impossible to find a doctor who has ever heard of it! Every doctor we dealt with never did.
We live in the NYC area. My husband was in Mt. Sinai Hospital. The doctor there referred all of his test results to the Mayo Clinic. They were the ones that diagnosed him and recommended what his treatment was. His treatment was a high dose of steroids orally, a immunosuppressant and several supplements that tapered down each month. He did this at home.
So far he able to walk again, but deals with lots of other issues from it.
If you read others that were treated, they had different treatments.
I wish you all the best in this rare and frustrating disease.