I must have missed that. If you could provide a link that would be great. I was under the impression that it was caused by an autoimmune disease.
I don't believe it has been PROVEN, but one side effect of the drugs Rush was using is hearing loss.
Abuse of painkiller could cause sudden hearing loss Story menitons specifically that Rush was taking the drugs implicated (according to his housekeeper) and, amazingly, that the institute where he was treated was among the first to discover the link.
A true tragedy, I am happy to see his prosthetic ears are working so well for him.