Making the diagnosis

My vet has tried without success to find out what is wrong with one of my dogs, so I am hoping that someone reading this blog has come across a similar case.
My dog is an 11-year-old mongrel (a collie-terrier cross type) weighing about 10kg. She was first blood-sampled about a year ago and this has since been repeated twice. Each time the results have suggested either a liver problem or Cushing's Disease (i.e high cortisol and alk./phos. levels). She has had an ultrasound scan of her liver and been tested for Cushing's three times (2 x ACTH and a dexamethasone test). The scan did not identify an obvious problem and she tested negative for Cushings each time. However, I am very worried about the long-term effects of her having a high cortisol level. She was initially blood-sampled because I noticed a significant change in her coat, and because she started drinking more than normal. Her coat is now shorter, finer and softer than previously, and she moults more - although she does not have any bald patches. She was drinking a large quantity in the evening and then was incontinent through the night - usually not emptying her bladder completely. The blood results showed normal kidney function, and therefore I now remove her water bowl at 8pm to prevent 'accidents' overnight. She doesn't appear to feel off-colour and can comfortably complete a 45 minute walk, provided it is not hot. Please, please can anyone help?
Claire Murison, by email

It can be notoriously hard to make a definitive diagnosis of hyperadrenocorticism or Cushing’s syndrome. Veterinary medicine is not an exact science! One reason is that we vets are much more aware of the possibility of Cushing’s syndrome than was the situation twenty years ago, so we are trying to diagnose it at an earlier stage.
It is not often that one encounters a dog showing all the classical signs of Cushing’s syndrome which include the three p’s (polyphagia or ravenous appetite, polyuria/polydipsia or increased urination and thirst), pot-belly, blackheads, bilaterally symmetrical hair loss on the flanks, and panting. There may be only a few of the signs present. One of my patients was investigated for a voracious appetite – that was the only sign of a problem that he showed. I am a little concerned, though, when you say that blood tests have shown a high cortisol level, as well as raised liver enzyme levels. I wonder whether you mean high cholesterol levels, which are a common finding on a basic blood screen for a patient with suspected Cushing’s syndrome, and would have led on to your vet advising the more specific stimulation and depression tests for Cushing’s syndrome.
If your dog does have raised cortisol levels, then it would be worth repeating the specific tests, and I think it would be worth doing that anyhow. I can think of at least two of my patients who have looked cushingoid to me but yielded negative or non-conclusive results on at least two occasions, but have eventually given positive results. It does happen!
If your dog has raised cholesterol levels, rather than cortisol levels, then a different endocrinological or hormonal problem might be present. Changes in hair coat occur with an underactive thyroid, for example.
Do go back to your vet because, as you rightly say, your dog does have a health problem which needs diagnosing.
Alison Logan, vet