Hi, I am new here and do not have a Yorkie yet, 2 Aussie's though. I'm looking in to becoming a vet tech and am studying common pet diseases before my interview. This article is really informative on Cushing's Disease - and you can ask a vet a question too
https://www.vetary.com/dog/condition/cushings-disease I'm sure once you get familiar with the condition, you'll do okay, the outlook is generally positive!