I did look for an article for you. Here is one that gives the top answers as fleas, ear mites, allergies, mange and infection.
Why are My Dog's Ears Losing Fur? | DailyPuppy.com and here is another
http://www.dailypuppy.com/articles/c...7-6f3f9f156ce8 -- this second one has more possibilities. and another:
http://www.lowchensaustralia.com/health/skin.htm which goes into more detail on skin conditions.
Allergies seems like they would cause itching in other areas and not just on the ears. But maybe that is just where it is showing most? Hope the vet gives some answers soon!