Konah got demoxdex at about 3 1/2 month. Our vet put him on Ivomec (ivermectin in the States) and his check 2 weeks ago was clear. His spots are already filling in and he looks about 80% better. If you don't treat them with anything, it gets insanely worse before it gets better (at least our vet said that) because the imune system has to kick in. An antihistamine can help with the scratching which might help with the hair loss. When Konah stopped scratching like a demon, we noticed his patches weren't getting much worse and actually seemed to get better.
I'm sure ivomec isn't great for a really long period of time, as any meds, but it sure did the trick with Konah bear. ALso, we noticed when we bathed him about twice a week (puppies and their incredible ability to find dirt) with a hydrating oatmeal shampoo, it helped A LOT! And both the regrowth and existing hair are equally soft and shiny.
Hope this helps. Good luck and healing vibes are being sent your way.
Erin and Konah Bear, The sqwooshy face boo man