Mystery Case

OK, for all you veterinary types that read this. Yeah, this means all, what, maybe one loyal follower left?? I have a case to see if anyone else has good input on that may be helpful. The children of the herd are overall doing well but the poodle is being a puzzle and any comments or suggestions would be appreciated...

12-13 year old, NM, miniature poodle. I adopted him in 2005 as an adult supposed to be about 8 at the time. Historically, he had terrible skin and was treated with a lot of steroids, antibiotics, and sensitive skin food. When I adopted him, I changed him to Purina HA and his skin cleared with only occasional outbreaks during really bad "allergy weather" and he has had no steroids since 2005 other than the small amount in ear ointments on occasion (rare). He has grade II/IV bilateral medial luxating patellas with associated osteoarthritis, asynchronous growth of the radius and ulna bilaterally with associated elbow dysplasia and osteoarthritis (too late to fix when I got him) resulting in right fore being slightly shorter than left, and luxated his left coxofemoral joint in 2007 this was repaired via closed reduction but he has a good bit of osteoarthritis in that joint as well. Neurologically, he had a presumptive episode of herniated cervical disk material in 2010 with clinical signs of neck pain and root signature that resolved with conservative therapy consisting of meloxicam, buprenorphine, and exercise restriction.

At the time of adoption, he was severely overweight and we have managed to reduce him to a consistent 14-15 pounds although he is still slightly overweight (BCS 6.5/9). He acclimated to the reduced diet and, while still more than willing to pick up an extra bite here and there, was not miserably hungry. When I feed him, I pre-soak the food then add water to help make him feel more full.

Lately, over the past 5-6 months, he is polyuric and polyphagic. He is not drinking any additional water than what is added to his food (measured out it does not exceed his expected daily intake) typically and is not getting any different food (i.e. increased sodium, etc.). He will urinate a huge puddle (as in imagine twice his size spread on the floor) then often a smaller puddle 5-10 minutes later. And yes, as indicated, he is breaking his housetraining when this occurs. He often needs to go as frequently as hourly but this is not a daily occurrence; very intermittent. During these periods, his abdomen will appear distended but not just with a large bladder. Non-painful, no palpable masses, then just as suddenly it appears normal again. Additionally, he acts as if he is starving constantly even pacing and unable to settle down at night to go to bed. I have not managed to measure the actual urine output yet.

Physical exam findings are boringly normal, no coat changes, prostate small and non-painful. Thoracic and abdominal radiographs taken in March were normal (need to repeat). Bloodwork from 2 weeks ago unremarkable, mild elevation of ALP, triglycerides. Thyroid values normal. I even did an ACTH stim reaching desperately that was totally normal. Have not done a full abdominal ultrasound yet (checked bladder about a month ago, normal) but that is next on the agenda.

So, given that complicated history, etc. any ideas floating around out there?????