Cushings False Negatives?

[MNPSP]

I have an 11-12 year old Boston Terrier (age assumed since he was a rescue). Summer of 2018, we took him to a new vet, and he said "Wow, has his fur always looked like this?" - his fur is rather thin, particularly under his legs and belly area. After talking to him for a bit, he suggested that he might have cushings. The dog drinks water like you wouldn't believe. His appetite is fine. He has a mild pot belly. Until the last month or so, we thought it was just something he could live with since he otherwise seemed happy, but he's started using the bathroom at night very frequently. A lot of times I will wake up and let him out, but if he can't wake one of us up, he has accidents, which is nearly nightly. In addition, he's started developing secondary skin infections, these scabby/oozy lesions. The vet put him on antibiotics and they cleared up, only to come back once the antibiotics were over. Since we love this dog and think he has several years left, we decided to look into finally treating and properly diagnosing the Cushings. We had the ACTH test done, assuming we would get a confirmation and start medicating, and basically the levels weren't enough to diagnose. I found this very frustrating, because I had researched the Vetoryl, and so many reviews online were positive and referred to so many of the symptoms we are dealing with as being resolved with use of the meds. Our vet suggested that it might be an early case (which doesn't make sense since he's been drinking water like this for almost two years) and suggested waiting 6 months and testing again, but frankly I can't keep waking up 3-4 times per night, and I know this poor dog hates going to the bathroom in the house. The vet said he was willing to start him on a super low dose (5mg) of the Vetoryl as a trial, but he is concerned about pushing him into Addison's and has given us a strict list of things to watch for (change in behavior, appetite, energy level, etc). My question is, has anyone else treated without an official diagnosis? Are there other tests we should try first?

[Bobo09]

My bichon was only diagnosed in may ‘19 so no expert but from what i have read on forums a dog should only get vetoryl if they have been officially diagnosed with cushings.
I now feel my bichon had cushings symptoms for around 2 years but they were always put down to something else, she also had numerous skin infections in 2018 which were treated with antibiotics only to return.
(During this time my dogs slept in the kitchen so i was not woken nightly, they had always slept there.)

[labblab]

Hello and welcome to you and your boy! To cut to the chase, yes, there is indeed another diagnostic test that can/should be performed and I’m honestly surprised that your vet has not recommended that it be done. In addition to the ACTH stimulation test, the other main diagnostic Cushing’s blood test is the LDDS (Low Dose Dexamethasone Suppression Test). Both tests have strengths and weaknesses, but for dogs who have no other known illnesses at the time of testing, the LDDS is generally preferred by most clinicians. This is because the LDDS is the more “sensitive” of the two tests — it is less likely to miss identifying Cushing’s in a dog who truly has the disease. It will reportedly identify Cushing’s 90-95% of the time in dogs who indeed have the disease. The flip side is that it is more likely than the ACTH to return a “false positive” if a dog is afflicted with some other illness. However, the ACTH does a much poorer job of signaling Cushing’s in all dogs that do have the disease (it returns far more “false negatives”). This is especially true if the Cushing’s is being caused by an adrenal tumor rather than a pituitary tumor. Here’s a more complete explanation of the LDDS testing protocol:

https://www.idexx.co.uk/files/low-dose-dexamethasone-suppression-test-protocol.pdf

So the bottom line is that, for a dog who exhibits symptom consistent with Cushing’s but who suffers from no other known illness at the time of testing, the LDDS is generally considered to be the better diagnostic choice. So I would immediately ask your vet to have this test performed, and I do wonder why he hasn’t suggested it on his own...

Marianne