Accepted Answer

Hi XXXXXXXXXX,
Drinking and urinating excessively can be a symptom of a number of different ailments, but the most common are diabetes mellitus, kidney disease, Cushing's disease, Addison's disease and hypercalcemia (usually secondary to cancer). Other, more rare causes, include diabetes insipidus and psychogenic polyuria and polydipisia.
You have already done the first step by taking your dog in for some blood and urine tests to evaluate for kidney disease, diabetes and signs of the other problems. To diagnose Cushing's or Addison's further, more specific, blood tests would need to be done. Cancer is usually diagnosed with abdominal ultrasound and chest X-rays.
Based on your dog's specific signs, she is very consistent with Cushing's disease. I would be happy to take a look at your dog's bloodwork if you can get it, and tell you what I thing.

If all of these tests yield no findings, then the dog should be evaluated for diabetes insipidus. This is a disease that is caused by a decrease in the synthesis or secretion of ADH (anti-diuretic hormone). This can happen secondary to a brain tumor, or it can be idiopathic (of unknown cause). There is also nephrogenic diabetes insipidus, in which the kidneys do not respond to ADH. The central diabetes insipidus can be tested for with a trial therapy with ADH. This is a treatable disease.
Psychogenic polyuria and polydipsia is exactly what it sounds like-the dog just drinks excessive amounts of water because it likes to, and therefore urinates excessively. This is not really a disease, but just an annoyance to the owner.
However, based on the fact that the increased thirst is not the only sign that your dog is showing, diabetes insipidus and psychogenic PU/PD would be unlikely as they would not cause the hyperactivity and weight loss.

I hope that this information is of help to you. Please let me know if I can be of further assistance.

Dr. K

Expert:	Dr. K
Pos. Feedback:	99.6 %
Accepts:	2972
Answered:	11/21/2008

Veterinarian

9 years experience as Veterinarian